|
I picked up a 475 on craigslist for $10. The owner stated it worked a couple years ago but when recently powered up, he "couldn't get a trace".
For $10, I figured it was worth the effort to fix it. I have experience fixing electronics and while my soldering/component testing/safety skills are pretty decent, my troubleshooting/tracing/etc is beginner level. Any help would be appreciated.
It came with a stand, the manual, two 10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe parts, etc), and the service manual. It also has the front cover and styrofoam intact. So the unit appears to have been kept well over the years.
I've opened the unit up and everything is surprisingly clean there as well. I see a couple of spots where the solder appears slightly burnt (like a semi-poor repair job, but not terrible). I've tested most components in those areas (but not all yet) and they have been testing fine.
Nothing appears terribly loose and nothing appears to be bubbled or blackened.
One major thing I've noticed is that all of the voltage readings are low. I read that most of them reference the +50V line and so I followed the manual's instructions to adjust that first. The best I can get is roughly 42.3V.
To me, that says I need to review the power section before anything else. Am I on the correct track, or not? Also, any common failure point that would cause my 50V line to drop?
Thanks for the help. I can post pictures of those help. Otherwise just let me know what other info would be useful.
|
Hi ....
Yes, until all of the low voltages are correct, nothing will
work properly in your 475.
One or more of the low voltage supplies is pulling all of the
voltages down.
Make a list of each low voltage the way it is now, and it will
probably be obvious which one(s) are bad.
If the 50 volt line is at 85% of what it should be, what
percentage are the other voltages of what they should be?
The Tekscopes Message archive has lots of information on your
problem if you care to look. The 475A, 465 and?465B are all about the same
as your 475 in the power supply area.
Common problems on 4xx power supplies are the full wave
bridges, the larger capacitors for each power supply voltage, and some pesky
Tantalum capacitors that are spread around the scope. The Tantalums that give
the most grief are in the 10 uF to 47 uF range and they are usually bright
colored "dipped" capacitors that go to ground.
My guess is that this will be a simple fix.
tom jobe...
PS If you have access to an ESR meter it might speed things
up, but it is not necessary.
?
?
?
?
?
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Saturday, July 07, 2012 4:01
PM
Subject: [TekScopes] Tektronix 475 with
no display
?
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a
trace".
For $10, I figured it was worth the effort to fix it. I have
experience fixing electronics and while my soldering/component testing/safety
skills are pretty decent, my troubleshooting/tracing/etc is beginner level.
Any help would be appreciated.
It came with a stand, the manual, two
10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe
parts, etc), and the service manual. It also has the front cover and styrofoam
intact. So the unit appears to have been kept well over the years.
I've
opened the unit up and everything is surprisingly clean there as well. I see a
couple of spots where the solder appears slightly burnt (like a semi-poor
repair job, but not terrible). I've tested most components in those areas (but
not all yet) and they have been testing fine.
Nothing appears terribly
loose and nothing appears to be bubbled or blackened.
One major thing
I've noticed is that all of the voltage readings are low. I read that most of
them reference the +50V line and so I followed the manual's instructions to
adjust that first. The best I can get is roughly 42.3V.
To me, that
says I need to review the power section before anything else. Am I on the
correct track, or not? Also, any common failure point that would cause my 50V
line to drop?
Thanks for the help. I can post pictures of those help.
Otherwise just let me know what other info would be useful.
|
Are you sure that your meter is reading correctly?
If your meter is correct then you should check the ripple level on
the 50V supply. If that is OK, then check the components in the
50V regulator.
On 2012-07-07 7:01 PM, i814u2.geo
wrote:
toggle quoted message
Show quoted text
I picked up a 475 on craigslist for $10. The owner stated it worked a couple years ago but when recently powered up, he "couldn't get a trace".
For $10, I figured it was worth the effort to fix it. I have experience fixing electronics and while my soldering/component testing/safety skills are pretty decent, my troubleshooting/tracing/etc is beginner level. Any help would be appreciated.
It came with a stand, the manual, two 10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe parts, etc), and the service manual. It also has the front cover and styrofoam intact. So the unit appears to have been kept well over the years.
I've opened the unit up and everything is surprisingly clean there as well. I see a couple of spots where the solder appears slightly burnt (like a semi-poor repair job, but not terrible). I've tested most components in those areas (but not all yet) and they have been testing fine.
Nothing appears terribly loose and nothing appears to be bubbled or blackened.
One major thing I've noticed is that all of the voltage readings are low. I read that most of them reference the +50V line and so I followed the manual's instructions to adjust that first. The best I can get is roughly 42.3V.
To me, that says I need to review the power section before anything else. Am I on the correct track, or not? Also, any common failure point that would cause my 50V line to drop?
Thanks for the help. I can post pictures of those help. Otherwise just let me know what other info would be useful.
|
That's a real nice deal. The 475 is a 200 MHz scope and is quite
nice.
?
The problem sounds like a bad electrolytic capacitor in the 50/105 volt
section of the power supply. Check C-1412 and C-1414. Most likely
C-1414?has high ESR and needs to be replaced. You might take a look through
the files and photos section as well as do a search through the messages for
capacitor replacement. The capacitor that most likely is bad is on the main
interface board grouped with some other can capacitors. You will want to be very
careful removing the bad cap as there is track under the can and it pulls up
easily as well as the plated through hole.
?
?
Good luck,
?
Tom
?
?
?
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Saturday, July 07, 2012 7:01
PM
Subject: [TekScopes] Tektronix 475 with
no display
?
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a
trace".
For $10, I figured it was worth the effort to fix it. I have
experience fixing electronics and while my soldering/component testing/safety
skills are pretty decent, my troubleshooting/tracing/etc is beginner level.
Any help would be appreciated.
It came with a stand, the manual, two
10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe
parts, etc), and the service manual. It also has the front cover and styrofoam
intact. So the unit appears to have been kept well over the years.
I've
opened the unit up and everything is surprisingly clean there as well. I see a
couple of spots where the solder appears slightly burnt (like a semi-poor
repair job, but not terrible). I've tested most components in those areas (but
not all yet) and they have been testing fine.
Nothing appears terribly
loose and nothing appears to be bubbled or blackened.
One major thing
I've noticed is that all of the voltage readings are low. I read that most of
them reference the +50V line and so I followed the manual's instructions to
adjust that first. The best I can get is roughly 42.3V.
To me, that
says I need to review the power section before anything else. Am I on the
correct track, or not? Also, any common failure point that would cause my 50V
line to drop?
Thanks for the help. I can post pictures of those help.
Otherwise just let me know what other info would be useful.
|
Thanks everyone:
I'll try to respond to everyone who has responded to me so far:
Yes, I've been searching the archives but getting a lot of generic results. I may just be using too many generic words in my searches (like "475 no display" or "475 power supply" etc). Since I wasn't completely sure of the issue, I wasn't completely sure of the search terms.
I've tested the voltages and these are the results:
+110 = 85.4 (77.6%)
+50 = 42.4 (84.8%)
+15 = 10.9 (72.667%)
+5 = 4.1 (82.0%)
-8 = -6.1 (76.3%)
(These readings are with the 50V adjustment cranked all the way up.)
I assume that is pointing to a larger issue with the 15V line, but if I'm off on that, let me know.
I'll check the specific caps mentioned, but otherwise it looks like the searching I have done is all pointing to the same things (mostly the tantalum caps or the main electrolytic ones).
Upon further review, I noticed that the "burnt" areas I initially saw were really just flux that wasn't cleaned up. I'm less worried about that now, but still paying attention to joints in those areas.
Also, I'm pretty sure my meter is accurate (based on readings from other items that match what I expected). I do not have an ESR or another scope at this time, so my testing is limited. I will be investigating my options for borrowing another scope to aid in my testing.
As I move along, I'll update this thread with my (hopeful) progress.
Thanks again everyone.
toggle quoted message
Show quoted text
--- In TekScopes@..., Merchison Burke <merchison@...> wrote:
Are you sure that your meter is reading correctly? If your meter is
correct then you should check the ripple level on the 50V supply. If
that is OK, then check the components in the 50V regulator.
On 2012-07-07 7:01 PM, i814u2.geo wrote:
I picked up a 475 on craigslist for $10. The owner stated it worked a couple years ago but when recently powered up, he "couldn't get a trace".
For $10, I figured it was worth the effort to fix it. I have experience fixing electronics and while my soldering/component testing/safety skills are pretty decent, my troubleshooting/tracing/etc is beginner level. Any help would be appreciated.
It came with a stand, the manual, two 10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe parts, etc), and the service manual. It also has the front cover and styrofoam intact. So the unit appears to have been kept well over the years.
I've opened the unit up and everything is surprisingly clean there as well. I see a couple of spots where the solder appears slightly burnt (like a semi-poor repair job, but not terrible). I've tested most components in those areas (but not all yet) and they have been testing fine.
Nothing appears terribly loose and nothing appears to be bubbled or blackened.
One major thing I've noticed is that all of the voltage readings are low. I read that most of them reference the +50V line and so I followed the manual's instructions to adjust that first. The best I can get is roughly 42.3V.
To me, that says I need to review the power section before anything else. Am I on the correct track, or not? Also, any common failure point that would cause my 50V line to drop?
Thanks for the help. I can post pictures of those help. Otherwise just let me know what other info would be useful.
|
Howdy and welcome.
You have found a great place to assist you with:
"~~~ my troubleshooting/tracing/etc. is beginner level. Any help would be
appreciated."
The following link contains a couple of generic resources to assist with
giving you a good logical troubleshooting methodology whatever kind of scope
(or other electronics for that matter) you work on.
s
I recommend you read -
Tek_Troubleshooting_Your_Oscilloscope_068-0315-00_89.pdf and
Tek_XYZ_Of_Oscilloscopes_1603.pdf at a minimum.
Power supply issues that affect all rails as your describing normally boils
down to two paths. 1.) The feed to the power supply is not generating enough
voltage/DC. This can be caused by many things, bad filter caps, open
rectifiers, misaligned 120V/220V selectors, etc...etc., etc.... 2.) One or
more regulated supplies are drawing the others down. This second path
invariably causes a higher than expected current draw.
In any event, my reason for responding was to give you the above resources
as a link. As far as the brief side track down initial trouble shooting
methodology/thinking it is meant to be a very high overview. One thing I
find useful however when I first partake of trouble shooting a power supply
issue is to take a look in the manual. Invariably the manual will give you a
"normal" current draw, wattage, etc. So by measuring the current draw of
the scope when it has the issue and comparing it to that in the manual you
can get an idea of if you will be heading down path 1 or 2 above. This is by
no means fool proof but I find it a good place to start getting my mind
around the issue. You can also measure resistance to ground as a good
indication. Tektronix is normally pretty good about giving you expected
values for this on each regulated supply..
In any event, I hope this is helpful. It is certain that there will be
others who will help you in a more specific way.
Rob
toggle quoted message
Show quoted text
-----Original Message----- From: TekScopes@... [mailto:TekScopes@...] On Behalf Of i814u2.geo Sent: Saturday, July 07, 2012 7:17 PM To: TekScopes@... Subject: [TekScopes] Re: Tektronix 475 with no display Thanks everyone: I'll try to respond to everyone who has responded to me so far: Yes, I've been searching the archives but getting a lot of generic results. I may just be using too many generic words in my searches (like "475 no display" or "475 power supply" etc). Since I wasn't completely sure of the issue, I wasn't completely sure of the search terms. I've tested the voltages and these are the results: +110 = 85.4 (77.6%) +50 = 42.4 (84.8%) +15 = 10.9 (72.667%) +5 = 4.1 (82.0%) -8 = -6.1 (76.3%) (These readings are with the 50V adjustment cranked all the way up.) I assume that is pointing to a larger issue with the 15V line, but if I'm off on that, let me know. I'll check the specific caps mentioned, but otherwise it looks like the searching I have done is all pointing to the same things (mostly the tantalum caps or the main electrolytic ones). Upon further review, I noticed that the "burnt" areas I initially saw were really just flux that wasn't cleaned up. I'm less worried about that now, but still paying attention to joints in those areas. Also, I'm pretty sure my meter is accurate (based on readings from other items that match what I expected). I do not have an ESR or another scope at this time, so my testing is limited. I will be investigating my options for borrowing another scope to aid in my testing. As I move along, I'll update this thread with my (hopeful) progress. Thanks again everyone. --- In TekScopes@..., Merchison Burke <merchison@...> wrote:
Are you sure that your meter is reading correctly? If your meter is
correct then you should check the ripple level on the 50V supply. If
that is OK, then check the components in the 50V regulator.
On 2012-07-07 7:01 PM, i814u2.geo wrote:
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a trace".
For $10, I figured it was worth the effort to fix it. I have experience
fixing electronics and while my soldering/component testing/safety skills are pretty decent, my troubleshooting/tracing/etc is beginner level. Any help would be appreciated.
It came with a stand, the manual, two 10x probes (one missing the 10x
pin, but otherwise intact), extra parts (probe parts, etc), and the service manual. It also has the front cover and styrofoam intact. So the unit appears to have been kept well over the years.
I've opened the unit up and everything is surprisingly clean there as
well. I see a couple of spots where the solder appears slightly burnt (like a semi-poor repair job, but not terrible). I've tested most components in those areas (but not all yet) and they have been testing fine.
Nothing appears terribly loose and nothing appears to be bubbled or
blackened.
One major thing I've noticed is that all of the voltage readings are
low. I read that most of them reference the +50V line and so I followed the manual's instructions to adjust that first. The best I can get is roughly 42.3V.
To me, that says I need to review the power section before anything
else. Am I on the correct track, or not? Also, any common failure point that would cause my 50V line to drop?
Thanks for the help. I can post pictures of those help. Otherwise just
let me know what other info would be useful.
------------------------------------ Yahoo! Groups Links
|
I did some more reading, and then more testing, over the past week. I also purchased an ESR meter to aid my testing.
What I found was that two of the main caps are definitely bad (one had too high of an ESR, roughly 100 times too high, based on average charts I found, and one appears to be an open circuit based on every test I performed).?
I removed those caps; despite all of the warnings about damaging traces, and being careful, I still damaged one pad/hole in the process of the first removal. ?I mention that just so others reading this will hopefully take more care in the future. Specifically, my damage was not from rough handling, but too much heat over time. I should have cooled things down in between changing the desoldering wick.
Luckily, the damaged part was only on the stand-alone circular pad on the bottom side (opposite the cap). I should be able to make a fair enough repair that won't affect the way it functions too much (if at all noticeable). The second cap came off with no issues as I took even more care removing that one (letting it cool down more in between solder removal, etc).
So this post has two purposes: 1) to say thanks for the info and pointers so far. C1414 (1000uf 75V) is the open cap and C1442 (5500uf 30v) is the bad one. 2) to ask whether it makes sense that my -15V line would be high (roughly -16.4) when the others are low (including -8 at roughly -6). From the schematic, it doesn't seem that -15V is related to either of these bad caps, so that was a bit confusing to me. Perhaps I'm missing something though.?
I'm now researching replacement capacitor options and hopefully that will fix everything. I'll know more once I get the new caps and adjust/test things. Any suggestions for caps would be welcomed. Otherwise, I'm searching the list now and various parts suppliers that I normally use (mouser, digikey, etc).
I assume the main reason people drill out the old ones and place new ones in there is mostly just for looks and partly for the 3 ground pins, correct? Is there any other benefit of going through that work, or should I just fit a new cap in there and jumper the ground pads where applicable?
Thanks again folks, much appreciated.
Josh
On Sat, Jul 7, 2012 at 6:47 PM, Tom Miller <tmiller11147@...> wrote:
?
That's a real nice deal. The 475 is a 200 MHz scope and is quite
nice.
?
The problem sounds like a bad electrolytic capacitor in the 50/105 volt
section of the power supply. Check C-1412 and C-1414. Most likely
C-1414?has high ESR and needs to be replaced. You might take a look through
the files and photos section as well as do a search through the messages for
capacitor replacement. The capacitor that most likely is bad is on the main
interface board grouped with some other can capacitors. You will want to be very
careful removing the bad cap as there is track under the can and it pulls up
easily as well as the plated through hole.
?
?
Good luck,
?
Tom
?
?
?
?
----- Original Message -----
Sent: Saturday, July 07, 2012 7:01
PM
Subject: [TekScopes] Tektronix 475 with
no display
?
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a
trace".
For $10, I figured it was worth the effort to fix it. I have
experience fixing electronics and while my soldering/component testing/safety
skills are pretty decent, my troubleshooting/tracing/etc is beginner level.
Any help would be appreciated.
It came with a stand, the manual, two
10x probes (one missing the 10x pin, but otherwise intact), extra parts (probe
parts, etc), and the service manual. It also has the front cover and styrofoam
intact. So the unit appears to have been kept well over the years.
I've
opened the unit up and everything is surprisingly clean there as well. I see a
couple of spots where the solder appears slightly burnt (like a semi-poor
repair job, but not terrible). I've tested most components in those areas (but
not all yet) and they have been testing fine.
Nothing appears terribly
loose and nothing appears to be bubbled or blackened.
One major thing
I've noticed is that all of the voltage readings are low. I read that most of
them reference the +50V line and so I followed the manual's instructions to
adjust that first. The best I can get is roughly 42.3V.
To me, that
says I need to review the power section before anything else. Am I on the
correct track, or not? Also, any common failure point that would cause my 50V
line to drop?
Thanks for the help. I can post pictures of those help.
Otherwise just let me know what other info would be useful.
|
Everything depends on the +50 supply. Even the regulator op amps get their
supply from the +50. So yes, you need to get the 50 volts working first.
?
I would find a radial lead cap (wire leads) that is at least higher in the
capacitance and voltage ratings?than the original can capacitors. Just
jumper the three ground holes together where needed.
?
For the 1000 uF try this:
?
For the 5500 uF try this:
?
?
?
HTH,
Tom
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Monday, July 16, 2012 10:50
AM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
I did some more reading, and then more testing, over the past week. I also
purchased an ESR meter to aid my testing.
What I found was that two of the main caps are definitely bad (one had
too high of an ESR, roughly 100 times too high, based on average charts I
found, and one appears to be an open circuit based on every test I
performed).?
I removed those caps; despite all of the warnings about damaging traces,
and being careful, I still damaged one pad/hole in the process of the first
removal. ?I mention that just so others reading this will hopefully take
more care in the future. Specifically, my damage was not from rough handling,
but too much heat over time. I should have cooled things down in between
changing the desoldering wick.
Luckily, the damaged part was only on the stand-alone circular pad on the
bottom side (opposite the cap). I should be able to make a fair enough repair
that won't affect the way it functions too much (if at all noticeable). The
second cap came off with no issues as I took even more care removing that one
(letting it cool down more in between solder removal, etc).
So this post has two purposes: 1) to say thanks for the info and pointers
so far. C1414 (1000uf 75V) is the open cap and C1442 (5500uf 30v) is the bad
one. 2) to ask whether it makes sense that my -15V line would be high (roughly
-16.4) when the others are low (including -8 at roughly -6). From the
schematic, it doesn't seem that -15V is related to either of these bad caps,
so that was a bit confusing to me. Perhaps I'm missing something
though.?
I'm now researching replacement capacitor options and hopefully that will
fix everything. I'll know more once I get the new caps and adjust/test things.
Any suggestions for caps would be welcomed. Otherwise, I'm searching the list
now and various parts suppliers that I normally use (mouser, digikey,
etc).
I assume the main reason people drill out the old ones and place new ones
in there is mostly just for looks and partly for the 3 ground pins, correct?
Is there any other benefit of going through that work, or should I just fit a
new cap in there and jumper the ground pads where applicable?
Thanks again folks, much appreciated.
Josh
On Sat, Jul 7, 2012 at 6:47 PM, Tom Miller <tmiller11147@...> wrote:
?
That's a real nice deal. The 475 is a 200 MHz scope and is quite
nice.
?
The problem sounds like a bad electrolytic capacitor in the 50/105 volt
section of the power supply. Check C-1412 and C-1414. Most likely
C-1414?has high ESR and needs to be replaced. You might take a look
through the files and photos section as well as do a search through the
messages for capacitor replacement. The capacitor that most likely is bad is
on the main interface board grouped with some other can capacitors. You will
want to be very careful removing the bad cap as there is track under the can
and it pulls up easily as well as the plated through hole.
?
?
Good luck,
?
Tom
?
?
?
?
----- Original Message -----
Sent: Saturday, July 07, 2012 7:01
PM
Subject: [TekScopes] Tektronix 475
with no display
?
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a
trace".
For $10, I figured it was worth the effort to fix
it. I have experience fixing electronics and while my soldering/component
testing/safety skills are pretty decent, my troubleshooting/tracing/etc is
beginner level. Any help would be appreciated.
It came with a
stand, the manual, two 10x probes (one missing the 10x pin, but otherwise
intact), extra parts (probe parts, etc), and the service manual. It also
has the front cover and styrofoam intact. So the unit appears to have been
kept well over the years.
I've opened the unit up and everything is
surprisingly clean there as well. I see a couple of spots where the solder
appears slightly burnt (like a semi-poor repair job, but not terrible).
I've tested most components in those areas (but not all yet) and they have
been testing fine.
Nothing appears terribly loose and nothing
appears to be bubbled or blackened.
One major thing I've noticed is
that all of the voltage readings are low. I read that most of them
reference the +50V line and so I followed the manual's instructions to
adjust that first. The best I can get is roughly 42.3V.
To me,
that says I need to review the power section before anything else. Am I on
the correct track, or not? Also, any common failure point that would cause
my 50V line to drop?
Thanks for the help. I can post pictures of
those help. Otherwise just let me know what other info would be
useful.
|
Great info, thanks. I was under the impression that I should replace with like-sized capacitance and at least similar voltage (higher being OK as well).? I assume the capacitance is OK to increase because it's a power supply and gets regulated afterword, correct?
Either way, I'll order some of those up and see what happens. I'm thinking I'll leave others alone, but I'm still internally re-hashing the age-old debate of whether or not to just replace all the big cans while I'm at it.
Thanks for the links as well.
Josh
On Mon, Jul 16, 2012 at 10:24 AM, Tom Miller <tmiller11147@...> wrote:
?
Everything depends on the +50 supply. Even the regulator op amps get their
supply from the +50. So yes, you need to get the 50 volts working first.
?
I would find a radial lead cap (wire leads) that is at least higher in the
capacitance and voltage ratings?than the original can capacitors. Just
jumper the three ground holes together where needed.
?
For the 1000 uF try this:
?
For the 5500 uF try this:
?
?
?
HTH,
Tom
?
----- Original Message -----
Sent: Monday, July 16, 2012 10:50
AM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
I did some more reading, and then more testing, over the past week. I also
purchased an ESR meter to aid my testing.
What I found was that two of the main caps are definitely bad (one had
too high of an ESR, roughly 100 times too high, based on average charts I
found, and one appears to be an open circuit based on every test I
performed).?
I removed those caps; despite all of the warnings about damaging traces,
and being careful, I still damaged one pad/hole in the process of the first
removal. ?I mention that just so others reading this will hopefully take
more care in the future. Specifically, my damage was not from rough handling,
but too much heat over time. I should have cooled things down in between
changing the desoldering wick.
Luckily, the damaged part was only on the stand-alone circular pad on the
bottom side (opposite the cap). I should be able to make a fair enough repair
that won't affect the way it functions too much (if at all noticeable). The
second cap came off with no issues as I took even more care removing that one
(letting it cool down more in between solder removal, etc).
So this post has two purposes: 1) to say thanks for the info and pointers
so far. C1414 (1000uf 75V) is the open cap and C1442 (5500uf 30v) is the bad
one. 2) to ask whether it makes sense that my -15V line would be high (roughly
-16.4) when the others are low (including -8 at roughly -6). From the
schematic, it doesn't seem that -15V is related to either of these bad caps,
so that was a bit confusing to me. Perhaps I'm missing something
though.?
I'm now researching replacement capacitor options and hopefully that will
fix everything. I'll know more once I get the new caps and adjust/test things.
Any suggestions for caps would be welcomed. Otherwise, I'm searching the list
now and various parts suppliers that I normally use (mouser, digikey,
etc).
I assume the main reason people drill out the old ones and place new ones
in there is mostly just for looks and partly for the 3 ground pins, correct?
Is there any other benefit of going through that work, or should I just fit a
new cap in there and jumper the ground pads where applicable?
Thanks again folks, much appreciated.
Josh
On Sat, Jul 7, 2012 at 6:47 PM, Tom Miller <tmiller11147@...> wrote:
?
That's a real nice deal. The 475 is a 200 MHz scope and is quite
nice.
?
The problem sounds like a bad electrolytic capacitor in the 50/105 volt
section of the power supply. Check C-1412 and C-1414. Most likely
C-1414?has high ESR and needs to be replaced. You might take a look
through the files and photos section as well as do a search through the
messages for capacitor replacement. The capacitor that most likely is bad is
on the main interface board grouped with some other can capacitors. You will
want to be very careful removing the bad cap as there is track under the can
and it pulls up easily as well as the plated through hole.
?
?
Good luck,
?
Tom
?
?
?
?
----- Original Message -----
Sent: Saturday, July 07, 2012 7:01
PM
Subject: [TekScopes] Tektronix 475
with no display
?
I picked up a 475 on craigslist for $10. The owner stated it worked a
couple years ago but when recently powered up, he "couldn't get a
trace".
For $10, I figured it was worth the effort to fix
it. I have experience fixing electronics and while my soldering/component
testing/safety skills are pretty decent, my troubleshooting/tracing/etc is
beginner level. Any help would be appreciated.
It came with a
stand, the manual, two 10x probes (one missing the 10x pin, but otherwise
intact), extra parts (probe parts, etc), and the service manual. It also
has the front cover and styrofoam intact. So the unit appears to have been
kept well over the years.
I've opened the unit up and everything is
surprisingly clean there as well. I see a couple of spots where the solder
appears slightly burnt (like a semi-poor repair job, but not terrible).
I've tested most components in those areas (but not all yet) and they have
been testing fine.
Nothing appears terribly loose and nothing
appears to be bubbled or blackened.
One major thing I've noticed is
that all of the voltage readings are low. I read that most of them
reference the +50V line and so I followed the manual's instructions to
adjust that first. The best I can get is roughly 42.3V.
To me,
that says I need to review the power section before anything else. Am I on
the correct track, or not? Also, any common failure point that would cause
my 50V line to drop?
Thanks for the help. I can post pictures of
those help. Otherwise just let me know what other info would be
useful.
|
On Mon, 16 Jul 2012 09:50:24 -0500, "fakecrap@..." <fakecrap@...> wrote: So this post has two purposes: 1) to say thanks for the info and pointers
so far. C1414 (1000uf 75V) is the open cap and C1442 (5500uf 30v) is the
bad one. 2) to ask whether it makes sense that my -15V line would be high
(roughly -16.4) when the others are low (including -8 at roughly -6). From
the schematic, it doesn't seem that -15V is related to either of these bad
caps, so that was a bit confusing to me. Perhaps I'm missing something
though. The -15V output uses the +50V output as a reference. The +50V output also powers the error amplifier for the +15V output which powers the error amplifier for the -15V output. I'm now researching replacement capacitor options and hopefully that will
fix everything. I'll know more once I get the new caps and adjust/test
things. Any suggestions for caps would be welcomed. Otherwise, I'm
searching the list now and various parts suppliers that I normally use
(mouser, digikey, etc).
I assume the main reason people drill out the old ones and place new ones
in there is mostly just for looks and partly for the 3 ground pins,
correct? Is there any other benefit of going through that work, or should I
just fit a new cap in there and jumper the ground pads where applicable? When I replaced the capacitors in my TM501, I just removed the old ones and used radial lead replacements. In that case, inexpensive radial lead replacements were the wrong form factor to fit inside of the old cans anyway. Next time I might keep the base with the pins to reuse instead of jumpering any unconnected pads but I would not bother keeping the whole can. I would not want to have to unsolder it from the board twice.
|
On Mon, 16 Jul 2012 10:25:01 -0500, "fakecrap@..." <fakecrap@...> wrote: Great info, thanks. I was under the impression that I should replace with
like-sized capacitance and at least similar voltage (higher being OK as
well). In high ripple current applications, sometimes higher voltage capacitors than strictly necessary are used because the larger physical size can dissipate more heat so they last longer. I assume the capacitance is OK to increase because it's a power supply and
gets regulated afterword, correct? It is fine within reason. Increasing the capacitance could increase the startup current or delay the startup in a switching power supply. In this case it is a standard 60Hz rectifier and capacitor filter so the surge current will be higher with more capacitance. I would use the same value or the next higher standard value if I was being conservative. Either way, I'll order some of those up and see what happens. I'm thinking
I'll leave others alone, but I'm still internally re-hashing the age-old
debate of whether or not to just replace all the big cans while I'm at it. If the failure is age related, then I usually replace all of the similar capacitors.
|
So I replaced the two capacitors (C1414 and C1442), reviewed the schematic and made sure that any connected points were still making contact (need to add a jumper from C1442 to CR1415, due to my removal accident where I damaged a trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to 50.0V and now I get the following: +50=50.0V +110=91.0V +15=15.0V +5=5V -15=-14.8V -8=-7.9V
+105=132.0V UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and possibly the 105 (at 132, schematic shows 136). I did some searching/testing and didn't see anything major wrong, so I tested the resistance values.
TP - expected - measured 110 - 11K - >20K (too high) 50 - 2.7K - 2.7K (perfect) 15 - 63 - 66.3 (within range) 5 - 46 - 49.9 (within range) -15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range) UNREG 50 - 14K - >20K (too high) 105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher resistance made sense to me. But the high resistance on the -15 line seemed odd. My assumption is that it means the voltage compensation is working overtime and properly correcting for an issue somewhere. Is that correct?
In reading the service manual, it states to attempt to test the rectifier, the current-limiting transistor, and the op amp. I see that the 105 and 110 both get fed from the +50V rectifier as well as the 110 op-amp pulling from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more. What I'm wondering is if anything I've stated throws an "obvious" flag for anyone with more experience. When I tested the current-limiting transistor for the 50V section, it had some voltage (the manual states it should be "off", which I take to mean 0V). I'm just not sure if that's the cause of the issue, or a result.
Based on some time staring at the manual, I'm assuming the rectifier is more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder button now (I did not previously). So some progress is being made (aside from the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before heading to work, just to make sure I had noted the proper values. When I did that, the voltage readings were better on 110 and 105 (94, 136.9 respectively). But as a minute or two went by, and things warmed up, the voltages started to drop. Again, this tends to make sense to me as something is most likely expanding, providing more resistance, and cutting down the potential. Any confirmation/correction would be appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest, not full-time) for at least 15 years, and I had a rough time replacing the caps. Everything works and tests out nicely, but it doesn't look so great (good joints, but heat marks, etc). I'm definitely not used to this older style of circuit board. Way too easy to lift traces, but that was a good lesson learned.
As always, thanks for all of the information. It's been greatly useful for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..."
< fakecrap@...> wrote:
>Great info, thanks. I was under the impression that I should replace with
>like-sized capacitance and at least similar voltage (higher being OK as
>well).
In high ripple current applications, sometimes higher voltage
capacitors than strictly necessary are used because the larger
physical size can dissipate more heat so they last longer.
>I assume the capacitance is OK to increase because it's a power supply and
>gets regulated afterword, correct?
It is fine within reason. Increasing the capacitance could increase
the startup current or delay the startup in a switching power supply.
In this case it is a standard 60Hz rectifier and capacitor filter so
the surge current will be higher with more capacitance. I would use
the same value or the next higher standard value if I was being
conservative.
>Either way, I'll order some of those up and see what happens. I'm thinking
>I'll leave others alone, but I'm still internally re-hashing the age-old
>debate of whether or not to just replace all the big cans while I'm at it.
If the failure is age related, then I usually replace all of the
similar capacitors.
|
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the schematic
and made sure that any connected points were still making contact (need to add
a jumper from C1442 to CR1415, due to my removal accident where I damaged a
trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to 50.0V
and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some searching/testing
and didn't see anything major wrong, so I tested the resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line seemed
odd. My assumption is that it means the voltage compensation is working
overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the 105
and 110 both get fed from the +50V rectifier as well as the 110 op-amp pulling
from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor for
the 50V section, it had some voltage (the manual states it should be "off",
which I take to mean 0V). I'm just not sure if that's the cause of the issue,
or a result.
Based on some time staring at the manual, I'm assuming the rectifier is
more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside from
the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before heading
to work, just to make sure I had noted the proper values. When I did that, the
voltage readings were better on 110 and 105 (94, 136.9 respectively). But as a
minute or two went by, and things warmed up, the voltages started to drop.
Again, this tends to make sense to me as something is most likely expanding,
providing more resistance, and cutting down the potential. Any
confirmation/correction would be appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest, not
full-time) for at least 15 years, and I had a rough time replacing the caps.
Everything works and tests out nicely, but it doesn't look so great (good
joints, but heat marks, etc). I'm definitely not used to this older style of
circuit board. Way too easy to lift traces, but that was a good lesson
learned.
As always, thanks for all of the information. It's been greatly useful
for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...>
wrote: >Great info, thanks. I was under the impression that I
should replace with >like-sized capacitance and at least similar
voltage (higher being OK as >well). In high ripple
current applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate more
heat so they last longer.
>I assume the capacitance is OK to increase because
it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the capacitance
could increase the startup current or delay the startup in a switching
power supply. In this case it is a standard 60Hz rectifier and capacitor
filter so the surge current will be higher with more capacitance. I would
use the same value or the next higher standard value if I was
being conservative.
>Either way, I'll order some of those up and see
what happens. I'm thinking
>I'll leave others alone, but I'm still
internally re-hashing the age-old
>debate of whether or not to just
replace all the big cans while I'm at it.
If the failure is age
related, then I usually replace all of the similar capacitors.
|
That is a daunting, if helpful, warning. I have a 465, 465B and a 475
and two of them need caps now. So there is a lot of this in my
future, and I don't want to lift traces, etc. It'd be nice if there
was a video with the "secrets", or at least tips ;-)
Ron
toggle quoted message
Show quoted text
On 7/19/12, fakecrap@... <fakecrap@...> wrote:
Also, again, those caps are tricky. I've been soldering (hobbiest, not
full-time) for at least 15 years, and I had a rough time replacing the
caps. Everything works and tests out nicely, but it doesn't look so great
(good joints, but heat marks, etc). I'm definitely not used to this older
style of circuit board. Way too easy to lift traces, but that was a good
lesson learned.
As always, thanks for all of the information. It's been greatly useful for
my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
**
On Mon, 16 Jul 2012 10:25:01 -0500, "fakecrap@..."
<fakecrap@...> wrote:
Great info, thanks. I was under the impression that I should replace
with
like-sized capacitance and at least similar voltage (higher being OK as
well). In high ripple current applications, sometimes higher voltage
capacitors than strictly necessary are used because the larger
physical size can dissipate more heat so they last longer.
I assume the capacitance is OK to increase because it's a power supply
and
gets regulated afterword, correct? It is fine within reason. Increasing the capacitance could increase
the startup current or delay the startup in a switching power supply.
In this case it is a standard 60Hz rectifier and capacitor filter so
the surge current will be higher with more capacitance. I would use
the same value or the next higher standard value if I was being
conservative.
Either way, I'll order some of those up and see what happens. I'm
thinking
I'll leave others alone, but I'm still internally re-hashing the age-old
debate of whether or not to just replace all the big cans while I'm at
it. If the failure is age related, then I usually replace all of the
similar capacitors.
|
Good Day,
you may gain something out of Ralf's homepage here??
There are some pictures which show the electrolytic caps (also called ELKOS in German) of a 475 model, which were at least partially replaced.
Some content of Ralf's homepage is in German only, I am afraid, but your favourite on-line translator shall help...
A few more general soldering tips can be found in the archives, but here is a quick write-up of what I can recommend.
Others may have different methods or recommendations, of course.
- Use the right soldering tool for the job (i.e. most beginners are surprised when they realize that modern SMD components similar to most power electronics components require fairly high power soldering tools). I use a 60-Watt Weller Type W60C for most soldering jobs.
- Good wetting and cleaning are both key. I am using the tacky solder flux from chipquick.com with great success and can recommend it (and no, I still do not have any affiliations with them, despite multiple recommendations I have given in the past...).
Standard IPA or Ethylalcohol work for most cleaning tasks; toothbrushes, paintbrushes and woodpicks are also useful helpers.
- When soldering larger components or areas, you may want to use a hot air gun for some moderate pre-heating.
Good Luck,
Magnus
toggle quoted message
Show quoted text
--- In TekScopes@..., Ron York <freelunch@...> wrote:
>
> That is a daunting, if helpful, warning. I have a 465, 465B and a 475
> and two of them need caps now.? So there is a lot of this in my
> future, and I don't want to lift traces, etc. It'd be nice if there
> was a video with the "secrets", or at least tips ;-)
>
>?? Ron
|
Unfortunately, I don't currently have access to another scope. Still haven't heard back from the guy I asked.
I did remove C1412 (350uf, 75V), but ESR seems fine (in and out of circuit). I tested the system with another cap (1000uf, 200V) but everything was the same. Did my (limited) choice of test capacitor affect my testing?
I started testing everything else I could last night. I wasn't finding too much wrong with simple components. The op-amp voltages were lower than the schematic shows (9.6 instead of 10.4, and 8.8 instead of 9.0), but swapping with a matching op-amp didn't change anything (for either the 50V section of the swapped section).
One odd thing, which was throwing me for a loop, was that the unreg 50V and the 105/160 test points were always low and I assumed that was partially why the 110V was only reading 94V. This morning, I powered it up to verify some numbers for this post. It was reading better on the the unreg 50 and 105/160 lines (roughly 66 and 136.6, respectively).
I tested some more expected voltages around the 110V area (as listed on the schematic) and found Q1496 transistor to be the first place that I saw only 93.x volts. I pulled that and it tested to be open with all +/- test variations (the ground was shorted to the case, of course, but the pin tests were all open).
I'll start by replacing that part next and hope it's the last piece of the puzzle. Any input on the capacitor would be appreciated as well. At this point, it seems like my C1412 is fine and I'll probably just place it back into the system.
Josh
On Jul 19, 2012, at 5:02 PM, Tom Miller wrote:
?
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the schematic
and made sure that any connected points were still making contact (need to add
a jumper from C1442 to CR1415, due to my removal accident where I damaged a
trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to 50.0V
and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some searching/testing
and didn't see anything major wrong, so I tested the resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line seemed
odd. My assumption is that it means the voltage compensation is working
overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the 105
and 110 both get fed from the +50V rectifier as well as the 110 op-amp pulling
from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor for
the 50V section, it had some voltage (the manual states it should be "off",
which I take to mean 0V). I'm just not sure if that's the cause of the issue,
or a result.
Based on some time staring at the manual, I'm assuming the rectifier is
more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside from
the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before heading
to work, just to make sure I had noted the proper values. When I did that, the
voltage readings were better on 110 and 105 (94, 136.9 respectively). But as a
minute or two went by, and things warmed up, the voltages started to drop.
Again, this tends to make sense to me as something is most likely expanding,
providing more resistance, and cutting down the potential. Any
confirmation/correction would be appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest, not
full-time) for at least 15 years, and I had a rough time replacing the caps.
Everything works and tests out nicely, but it doesn't look so great (good
joints, but heat marks, etc). I'm definitely not used to this older style of
circuit board. Way too easy to lift traces, but that was a good lesson
learned.
As always, thanks for all of the information. It's been greatly useful
for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...>
wrote: >Great info, thanks. I was under the impression that I
should replace with >like-sized capacitance and at least similar
voltage (higher being OK as >well). In high ripple
current applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate more
heat so they last longer.
>I assume the capacitance is OK to increase because
it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the capacitance
could increase the startup current or delay the startup in a switching
power supply. In this case it is a standard 60Hz rectifier and capacitor
filter so the surge current will be higher with more capacitance. I would
use the same value or the next higher standard value if I was
being conservative.
>Either way, I'll order some of those up and see
what happens. I'm thinking
>I'll leave others alone, but I'm still
internally re-hashing the age-old
>debate of whether or not to just
replace all the big cans while I'm at it.
If the failure is age
related, then I usually replace all of the similar capacitors.
|
Ok, that's good. You might check the bridge rectifier diodes. You might
have one diode open. Or maybe just replace it anyway. I have gotten them from
radio shack - I think it is a 400 volt bridge.
?
Tom
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Saturday, July 21, 2012 12:20
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
Unfortunately, I don't currently have access to another scope. Still
haven't heard back from the guy I asked.
I did remove C1412 (350uf, 75V), but ESR seems fine (in and out of
circuit). I tested the system with another cap (1000uf, 200V) but everything
was the same. Did my (limited) choice of test capacitor affect my
testing?
I started testing everything else I could last night. I wasn't finding
too much wrong with simple components. The op-amp voltages were lower than the
schematic shows (9.6 instead of 10.4, and 8.8 instead of 9.0), but swapping
with a matching op-amp didn't change anything (for either the 50V section of
the swapped section).
One odd thing, which was throwing me for a loop, was that the unreg 50V
and the 105/160 test points were always low and I assumed that was partially
why the 110V was only reading 94V. This morning, I powered it up to verify
some numbers for this post. It was reading better on the the unreg 50 and
105/160 lines (roughly 66 and 136.6, respectively).
I tested some more expected voltages around the 110V area (as listed on
the schematic) and found Q1496 transistor to be the first place that I saw
only 93.x volts. I pulled that and it tested to be open with all +/- test
variations (the ground was shorted to the case, of course, but the pin tests
were all open).
I'll start by replacing that part next and hope it's the last piece of
the puzzle.
Any input on the capacitor would be appreciated as well. At this point,
it seems like my C1412 is fine and I'll probably just place it back into the
system.
Josh
On Jul 19, 2012, at 5:02 PM, Tom Miller wrote:
?
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix
475 with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the
schematic and made sure that any connected points were still making
contact (need to add a jumper from C1442 to CR1415, due to my removal
accident where I damaged a trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to
50.0V and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some
searching/testing and didn't see anything major wrong, so I tested the
resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line
seemed odd. My assumption is that it means the voltage compensation is
working overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the
105 and 110 both get fed from the +50V rectifier as well as the 110 op-amp
pulling from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor
for the 50V section, it had some voltage (the manual states it should be
"off", which I take to mean 0V). I'm just not sure if that's the cause of
the issue, or a result.
Based on some time staring at the manual, I'm assuming the rectifier
is more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside
from the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before
heading to work, just to make sure I had noted the proper values. When I
did that, the voltage readings were better on 110 and 105 (94, 136.9
respectively). But as a minute or two went by, and things warmed up, the
voltages started to drop. Again, this tends to make sense to me as
something is most likely expanding, providing more resistance, and cutting
down the potential. Any confirmation/correction would be
appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest,
not full-time) for at least 15 years, and I had a rough time replacing the
caps. Everything works and tests out nicely, but it doesn't look so great
(good joints, but heat marks, etc). I'm definitely not used to this older
style of circuit board. Way too easy to lift traces, but that was a good
lesson learned.
As always, thanks for all of the information. It's been greatly
useful for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...> wrote: >Great info,
thanks. I was under the impression that I should replace
with >like-sized capacitance and at least similar voltage (higher
being OK as >well). In high ripple current
applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate
more heat so they last longer.
>I assume the capacitance is OK to increase
because it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the
capacitance could increase the startup current or delay the startup
in a switching power supply. In this case it is a standard 60Hz
rectifier and capacitor filter so the surge current will be higher
with more capacitance. I would use the same value or the next higher
standard value if I was being conservative.
>Either way, I'll order some of those up and
see what happens. I'm thinking
>I'll leave others alone, but I'm
still internally re-hashing the age-old
>debate of whether or not
to just replace all the big cans while I'm at it.
If the
failure is age related, then I usually replace all of the similar
capacitors.
|
Last night I pulled CR1412 and it appeared to test properly. CR1489 (diode on the 110 line) I believe I've tested but I'll test again to be certain. If the Q1496 replacement doesn't go well, I'll re-investigate the rectifiers.
I can't seem to find specs on Q1496 yet. From my searching on Mouser's site, it looks like I need to know a bit more than just my assumptions (minimum of 140V, PNP, bipolar, TO39 casing). Does anyone know the details I need to know to choose the proper replacement, or can I just use the bits I do know to select one?
-Josh
On Jul 21, 2012, at 11:43 AM, Tom Miller wrote:
?
Ok, that's good. You might check the bridge rectifier diodes. You might
have one diode open. Or maybe just replace it anyway. I have gotten them from
radio shack - I think it is a 400 volt bridge.
?
Tom
?
----- Original Message -----
Sent: Saturday, July 21, 2012 12:20
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
Unfortunately, I don't currently have access to another scope. Still
haven't heard back from the guy I asked.
I did remove C1412 (350uf, 75V), but ESR seems fine (in and out of
circuit). I tested the system with another cap (1000uf, 200V) but everything
was the same. Did my (limited) choice of test capacitor affect my
testing?
I started testing everything else I could last night. I wasn't finding
too much wrong with simple components. The op-amp voltages were lower than the
schematic shows (9.6 instead of 10.4, and 8.8 instead of 9.0), but swapping
with a matching op-amp didn't change anything (for either the 50V section of
the swapped section).
One odd thing, which was throwing me for a loop, was that the unreg 50V
and the 105/160 test points were always low and I assumed that was partially
why the 110V was only reading 94V. This morning, I powered it up to verify
some numbers for this post. It was reading better on the the unreg 50 and
105/160 lines (roughly 66 and 136.6, respectively).
I tested some more expected voltages around the 110V area (as listed on
the schematic) and found Q1496 transistor to be the first place that I saw
only 93.x volts. I pulled that and it tested to be open with all +/- test
variations (the ground was shorted to the case, of course, but the pin tests
were all open).
I'll start by replacing that part next and hope it's the last piece of
the puzzle.
Any input on the capacitor would be appreciated as well. At this point,
it seems like my C1412 is fine and I'll probably just place it back into the
system.
Josh
On Jul 19, 2012, at 5:02 PM, Tom Miller wrote:
?
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix
475 with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the
schematic and made sure that any connected points were still making
contact (need to add a jumper from C1442 to CR1415, due to my removal
accident where I damaged a trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to
50.0V and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some
searching/testing and didn't see anything major wrong, so I tested the
resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line
seemed odd. My assumption is that it means the voltage compensation is
working overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the
105 and 110 both get fed from the +50V rectifier as well as the 110 op-amp
pulling from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor
for the 50V section, it had some voltage (the manual states it should be
"off", which I take to mean 0V). I'm just not sure if that's the cause of
the issue, or a result.
Based on some time staring at the manual, I'm assuming the rectifier
is more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside
from the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before
heading to work, just to make sure I had noted the proper values. When I
did that, the voltage readings were better on 110 and 105 (94, 136.9
respectively). But as a minute or two went by, and things warmed up, the
voltages started to drop. Again, this tends to make sense to me as
something is most likely expanding, providing more resistance, and cutting
down the potential. Any confirmation/correction would be
appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest,
not full-time) for at least 15 years, and I had a rough time replacing the
caps. Everything works and tests out nicely, but it doesn't look so great
(good joints, but heat marks, etc). I'm definitely not used to this older
style of circuit board. Way too easy to lift traces, but that was a good
lesson learned.
As always, thanks for all of the information. It's been greatly
useful for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...> wrote: >Great info,
thanks. I was under the impression that I should replace
with >like-sized capacitance and at least similar voltage (higher
being OK as >well). In high ripple current
applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate
more heat so they last longer.
>I assume the capacitance is OK to increase
because it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the
capacitance could increase the startup current or delay the startup
in a switching power supply. In this case it is a standard 60Hz
rectifier and capacitor filter so the surge current will be higher
with more capacitance. I would use the same value or the next higher
standard value if I was being conservative.
>Either way, I'll order some of those up and
see what happens. I'm thinking
>I'll leave others alone, but I'm
still internally re-hashing the age-old
>debate of whether or not
to just replace all the big cans while I'm at it.
If the
failure is age related, then I usually replace all of the similar
capacitors.
|
Also, this is the tek ?part number: 151-0280-00 (the casing also has the number 536 printed on it).
On Jul 21, 2012, at 11:43 AM, Tom Miller wrote:
?
Ok, that's good. You might check the bridge rectifier diodes. You might
have one diode open. Or maybe just replace it anyway. I have gotten them from
radio shack - I think it is a 400 volt bridge.
?
Tom
?
----- Original Message -----
Sent: Saturday, July 21, 2012 12:20
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
Unfortunately, I don't currently have access to another scope. Still
haven't heard back from the guy I asked.
I did remove C1412 (350uf, 75V), but ESR seems fine (in and out of
circuit). I tested the system with another cap (1000uf, 200V) but everything
was the same. Did my (limited) choice of test capacitor affect my
testing?
I started testing everything else I could last night. I wasn't finding
too much wrong with simple components. The op-amp voltages were lower than the
schematic shows (9.6 instead of 10.4, and 8.8 instead of 9.0), but swapping
with a matching op-amp didn't change anything (for either the 50V section of
the swapped section).
One odd thing, which was throwing me for a loop, was that the unreg 50V
and the 105/160 test points were always low and I assumed that was partially
why the 110V was only reading 94V. This morning, I powered it up to verify
some numbers for this post. It was reading better on the the unreg 50 and
105/160 lines (roughly 66 and 136.6, respectively).
I tested some more expected voltages around the 110V area (as listed on
the schematic) and found Q1496 transistor to be the first place that I saw
only 93.x volts. I pulled that and it tested to be open with all +/- test
variations (the ground was shorted to the case, of course, but the pin tests
were all open).
I'll start by replacing that part next and hope it's the last piece of
the puzzle.
Any input on the capacitor would be appreciated as well. At this point,
it seems like my C1412 is fine and I'll probably just place it back into the
system.
Josh
On Jul 19, 2012, at 5:02 PM, Tom Miller wrote:
?
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix
475 with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the
schematic and made sure that any connected points were still making
contact (need to add a jumper from C1442 to CR1415, due to my removal
accident where I damaged a trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to
50.0V and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some
searching/testing and didn't see anything major wrong, so I tested the
resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line
seemed odd. My assumption is that it means the voltage compensation is
working overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the
105 and 110 both get fed from the +50V rectifier as well as the 110 op-amp
pulling from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor
for the 50V section, it had some voltage (the manual states it should be
"off", which I take to mean 0V). I'm just not sure if that's the cause of
the issue, or a result.
Based on some time staring at the manual, I'm assuming the rectifier
is more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside
from the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before
heading to work, just to make sure I had noted the proper values. When I
did that, the voltage readings were better on 110 and 105 (94, 136.9
respectively). But as a minute or two went by, and things warmed up, the
voltages started to drop. Again, this tends to make sense to me as
something is most likely expanding, providing more resistance, and cutting
down the potential. Any confirmation/correction would be
appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest,
not full-time) for at least 15 years, and I had a rough time replacing the
caps. Everything works and tests out nicely, but it doesn't look so great
(good joints, but heat marks, etc). I'm definitely not used to this older
style of circuit board. Way too easy to lift traces, but that was a good
lesson learned.
As always, thanks for all of the information. It's been greatly
useful for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...> wrote: >Great info,
thanks. I was under the impression that I should replace
with >like-sized capacitance and at least similar voltage (higher
being OK as >well). In high ripple current
applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate
more heat so they last longer.
>I assume the capacitance is OK to increase
because it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the
capacitance could increase the startup current or delay the startup
in a switching power supply. In this case it is a standard 60Hz
rectifier and capacitor filter so the surge current will be higher
with more capacitance. I would use the same value or the next higher
standard value if I was being conservative.
>Either way, I'll order some of those up and
see what happens. I'm thinking
>I'll leave others alone, but I'm
still internally re-hashing the age-old
>debate of whether or not
to just replace all the big cans while I'm at it.
If the
failure is age related, then I usually replace all of the similar
capacitors.
|
One place claims that this is a replacement:
This is the place:
If that all seems legit, I'll just use those specs to check some local places and then order from the internet if needed.
-Josh
On Jul 21, 2012, at 11:43 AM, Tom Miller wrote:
?
Ok, that's good. You might check the bridge rectifier diodes. You might
have one diode open. Or maybe just replace it anyway. I have gotten them from
radio shack - I think it is a 400 volt bridge.
?
Tom
?
----- Original Message -----
Sent: Saturday, July 21, 2012 12:20
PM
Subject: Re: [TekScopes] Tektronix 475
with no display
?
Unfortunately, I don't currently have access to another scope. Still
haven't heard back from the guy I asked.
I did remove C1412 (350uf, 75V), but ESR seems fine (in and out of
circuit). I tested the system with another cap (1000uf, 200V) but everything
was the same. Did my (limited) choice of test capacitor affect my
testing?
I started testing everything else I could last night. I wasn't finding
too much wrong with simple components. The op-amp voltages were lower than the
schematic shows (9.6 instead of 10.4, and 8.8 instead of 9.0), but swapping
with a matching op-amp didn't change anything (for either the 50V section of
the swapped section).
One odd thing, which was throwing me for a loop, was that the unreg 50V
and the 105/160 test points were always low and I assumed that was partially
why the 110V was only reading 94V. This morning, I powered it up to verify
some numbers for this post. It was reading better on the the unreg 50 and
105/160 lines (roughly 66 and 136.6, respectively).
I tested some more expected voltages around the 110V area (as listed on
the schematic) and found Q1496 transistor to be the first place that I saw
only 93.x volts. I pulled that and it tested to be open with all +/- test
variations (the ground was shorted to the case, of course, but the pin tests
were all open).
I'll start by replacing that part next and hope it's the last piece of
the puzzle.
Any input on the capacitor would be appreciated as well. At this point,
it seems like my C1412 is fine and I'll probably just place it back into the
system.
Josh
On Jul 19, 2012, at 5:02 PM, Tom Miller wrote:
?
I think you need to change C-1412 also.
?
Can you take a look at the ripple on the 110 volt?test point? Be
careful. 110 volts hurts a bit.
?
Tom
?
----- Original Message -----
Sent: Thursday, July 19, 2012 5:31
PM
Subject: Re: [TekScopes] Tektronix
475 with no display
?
So I replaced the two capacitors (C1414 and C1442), reviewed the
schematic and made sure that any connected points were still making
contact (need to add a jumper from C1442 to CR1415, due to my removal
accident where I damaged a trace).?
I backed off the +50V adjustment, fired it up, adjusted it back to
50.0V and now I get the following:
+50=50.0V
+110=91.0V
+15=15.0V
+5=5V
-15=-14.8V
-8=-7.9V
+105=132.0V
UNREG 50=~66V
Now, those all look to be within spec except for +110 (at 91V) and
possibly the 105 (at 132, schematic shows 136). I did some
searching/testing and didn't see anything major wrong, so I tested the
resistance values.
TP - expected - measured
110 - 11K - >20K (too high)
50 - 2.7K - 2.7K (perfect)
15 - 63 - 66.3 (within range)
5 - 46 - 49.9 (within range)
-15 - 480 - 12.9K (too high)
-8 - 32 - 31.2 (within range)
UNREG 50 - 14K - >20K (too high)
105 - 12K - >20K (too high)
So my 110 and 105 lines are both showing low voltage, so the higher
resistance made sense to me. But the high resistance on the -15 line
seemed odd. My assumption is that it means the voltage compensation is
working overtime and properly correcting for an issue somewhere. Is that
correct?
In reading the service manual, it states to attempt to test the
rectifier, the current-limiting transistor, and the op amp. I see that the
105 and 110 both get fed from the +50V rectifier as well as the 110 op-amp
pulling from the regulated 50V line.
When I get home from work, I intend to test the 50V supply area more.
What I'm wondering is if anything I've stated throws an "obvious" flag for
anyone with more experience. When I tested the current-limiting transistor
for the 50V section, it had some voltage (the manual states it should be
"off", which I take to mean 0V). I'm just not sure if that's the cause of
the issue, or a result.
Based on some time staring at the manual, I'm assuming the rectifier
is more of an issue, but that's a guess.
Also, as a side note, I can get a line when I press the beam finder
button now (I did not previously). So some progress is being made (aside
from the obvious progress of mostly-proper voltages).
One final thing to mention: This morning I powered it up before
heading to work, just to make sure I had noted the proper values. When I
did that, the voltage readings were better on 110 and 105 (94, 136.9
respectively). But as a minute or two went by, and things warmed up, the
voltages started to drop. Again, this tends to make sense to me as
something is most likely expanding, providing more resistance, and cutting
down the potential. Any confirmation/correction would be
appreciated.
Also, again, those caps are tricky. I've been soldering (hobbiest,
not full-time) for at least 15 years, and I had a rough time replacing the
caps. Everything works and tests out nicely, but it doesn't look so great
(good joints, but heat marks, etc). I'm definitely not used to this older
style of circuit board. Way too easy to lift traces, but that was a good
lesson learned.
As always, thanks for all of the information. It's been greatly
useful for my learning process.
-Josh
On Mon, Jul 16, 2012 at 11:08 AM, David <davidwhess@...> wrote:
?
On Mon, 16 Jul 2012 10:25:01 -0500, " fakecrap@..." < fakecrap@...> wrote: >Great info,
thanks. I was under the impression that I should replace
with >like-sized capacitance and at least similar voltage (higher
being OK as >well). In high ripple current
applications, sometimes higher voltage capacitors than strictly
necessary are used because the larger physical size can dissipate
more heat so they last longer.
>I assume the capacitance is OK to increase
because it's a power supply and
>gets regulated afterword,
correct?
It is fine within reason. Increasing the
capacitance could increase the startup current or delay the startup
in a switching power supply. In this case it is a standard 60Hz
rectifier and capacitor filter so the surge current will be higher
with more capacitance. I would use the same value or the next higher
standard value if I was being conservative.
>Either way, I'll order some of those up and
see what happens. I'm thinking
>I'll leave others alone, but I'm
still internally re-hashing the age-old
>debate of whether or not
to just replace all the big cans while I'm at it.
If the
failure is age related, then I usually replace all of the similar
capacitors.
|
David Hess