533A and 466 in Rochester
I have no affiliation with the seller.
-Kurt
|
Re: 7B92A with tunnel diodes vs. version without
Hi Raymond,
Tried a tunnel diode based 7B92 in a 7904A/7A29, with input from a TG501 and internal triggering. At 2 ns and 1 ns the TG501 "pulse" stream is nearly a sine wave. At 2 ns (500 MHz) the 7B92 triggers well in Norm mode with signal less than 0.5 div. At 1 ns (1 GHz) it fails in Norm mode but syncs in HF Sync mode (and signal far below 0.5 div). But a 7B15 performed far better with a much sharper trace, so with much less jitter. Even at 1 GHz the 7B15 would trigger in Norm mode.
Checking TB performance this way in a 7904(A) is somewhat undefined since it's not clear what trigger amplitude arrives at the TB. Testing in a 7104 would give better information.
The 7B92 was "as is", so other units might perform better.
Albert
toggle quoted message
Show quoted text
Tried my newly acquired SG504 (with leveling head) and saw this 7B92A triggering happily at around 1.05 GHz on my 7904 + 7A19... Of course, amplitude isn't shown anywhere near correctly. 7B92A is specified to trigger "above 500MHz".
Raymond
|
Re: 7000 series on screen graphics question 7704A versus 7633
Chris - where do you live - I'm happy for you to visit me in
Kenilworth, Warwickshire with the scope if you are unhappy to fiddle with it yourself. Regards,
David Partridge I am just north of Shrewsbury, but being in the race car game I get to travel about a lot, so I could drop it in at a mutually agreeable time? You aren't that far away at all, in the grand scheme of things. I don't mind fiddling with stuff, but this to me is pretty darned complex, and I would hate to do it a mischief. If you want to e-mail me I am at chris (at) chriswilson.tv I would be most grateful if you could find time to take a look at it at some stage, even if it's to tell me that they are all like that ;) Thanks David 16/07/2012 21:55 -- Best Regards, Chris Wilson.
|
Hi Mark,
same symptoms as mine¡. drop the connection to the hv multiplier block, one wire from t1475, right at the block.
replace Q1380 and check Q1378 and Q1381,be careful , these transistors have non standard pin outs.
replace the fuse,, try again¡..if it runs¡.. the block is probabbly breaking down under hv. this load reflects back on the transistors¡..they overheat and go into thermal runaway, short and bye bye¡..
i've replaced three of the blocks, 2 sc504's 1 sc503¡.
they are hard to find¡.
but the scope is worth it¡.
jim
toggle quoted message
Show quoted text
On Jul 16, 2012, at 9:14 AM, Mark Wendt wrote: Jim,
The current problem with this guy is something is drawing so much power
it causes Q1380 on the main board to blow. Q1381 is okay. When Q1380
goes, it also takes F3488 with it.
On 07/16/2012 10:31 AM, Jim Popwell Jr wrote:
what's up mark? I have an sc504 that i had problem with.
mine turned out to be the hv multiplier.
jim
On Jul 16, 2012, at 2:44 AM, Mark Wendt wrote:
On 07/15/2012 12:57 PM, keithostertag wrote:
Good News! We now have a working CRT and R7903!
The Short story: After replacing one resistor the screen came alive. After some adjustments there are two items remaining with this project that I need help with:
1. The readouts only gives one numeral. For instance, .5uS, 5uS, and 50uS all display as 5uS. Similarly, .5V, 5mV, and 50mV all say 5mV. Same for all settings, and regardless which plugins I use. The 10X multiplier makes no difference in the Readout display, though it does make it a little "wavy", like a slight vibration. Also, the Readouts are positioned a little low on the screen, so that the lower ones are half-obscured off the bottom of CRT frame.
2.) I'm going to need a source for some of the push-button switches on the front panel.
The longer story (for those interested):
I was following Albert's suggestion to check the continuity around P1675 when I found pin 3 to TP1883 measured around 5Meg ohms. When I went to touch one side of R1880 in order to lift it, it literally fell apart into two clean pieces. No burn or stress marks of any kind- and nothing else on that board was found bad.
After replacing R1880 the CRT came right up, and I went through both the PS cal as well as the z-axis cal. The are a few sections of the z-axis cal that I can't do (I guess) since I don't have a marker generator. (?)
I want to say that after all these weeks of working on this project I was immensely happy and relieved to see that first trace appear! My guess is that this R7903 had been sitting unused (due to its broken condition) for many years before it got to me. Many caps needed to be replaced on several boards, mostly the PS. Of course I would not have been able to do this without your help and instruction, and I am grateful for your patience and perseverance. Really a good example of group effort!
I know even _less_ about logic circuits than I do analog circuits, so fixing this Readout problem will be very interesting. I am reading the manual...
Your thoughts on how to approach the Readout problem?
Thanks,
Keith Ostertag
Keith,
Congrats on finally getting to the root of the problem. Now, if I could
only have that "Ah Ha!" moment on this damn SC504 I've got. ;-)
Mark
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
|
Re: 7000 series on screen graphics question 7704A versus 7633
I haven't followed the thread but several years ago I was working on a 7704A
that had characters that weren't stable vertically. There?were adjustments on
the backplane / vertical interface board (I don't remember?what they were
called) that ended up fixing the problem. They were a pain to get to and someone
on the list suggested it several times before I finally?tweaked?them. I had
spent several hours?trying board?swaps and other things with no success and the
adjustment?removed all the jitter and gave me a solid display.
?Jim W4JBM
"With a soldering iron in one hand, a schematic in the other, and a puzzled look
on his face..."
|
Re: 7000 series on screen graphics question 7704A versus 7633
Chris - where do you live - I'm happy for you to visit me in Kenilworth, Warwickshire with the scope if you are unhappy to fiddle with it yourself.
Regards,
David Partridge
toggle quoted message
Show quoted text
-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of chrismwilsonuk
Sent: 16 July 2012 21:16
To: TekScopes@...
Subject: [TekScopes] Re: 7000 series on screen graphics question 7704A versus 7633
I don't feel 100% confident fiddling with it that deeply, to be honest Jim. if it was an old nail, no worries, but with it being brand new old stock I would rather pay someone that knows what they are doing to have a look, or to just try another display board. I'd kick myself if I @#~%$*@ it up ;) I know it's not worth a lot, but it's kind of nice being "new", I doubt I'd find another very easily. Thanks for the detailed reply Jim.
|
Re: 7000 series on screen graphics question 7704A versus 7633
--- In TekScopes@..., Jim Popwell Jr <jpopwell@...> wrote:
HI CHRIS,
I would do the astig and refocus¡.astig¡and refocus for sharpest beam definition. use the calibrator and adjust for best looking sq wave¡then kill the vert deflection and the horz deflection¡turn the intensity down and adjust both again for the sharpest spot¡.increase the intensity and readjust both again¡then go back to normal sweep¡¡.
NOW DO THE CAL procedure on the display bd.
there are a couple of adjustments on the bd that will straighten out the "jumpy double" characters.
won't take much time but will make a big difference.
if i remember right these characters were created by different currents at different times¡ so a little too much or too little current misshaped the characters.
i often find the right controls, then adjust them by eye for best display, by finding the sweet spot of the adjustment. i.e. find the ends of the range where the adjustment makes a total mess with the adjustment one way then going back thru the best look¡until you get a mess again¡¡...then splitting the difference.
jim
I don't feel 100% confident fiddling with it that deeply, to be honest Jim. if it was an old nail, no worries, but with it being brand new old stock I would rather pay someone that knows what they are doing to have a look, or to just try another display board. I'd kick myself if I @#~%$*@ it up ;) I know it's not worth a lot, but it's kind of nice being "new", I doubt I'd find another very easily. Thanks for the detailed reply Jim.
|
Re: 7000 series on screen graphics question 7704A versus 7633
16/07/2012 21:06
Thanks for the replies re this issue. Whilst I agree the "hand drawn"
quality is somewhat charming my old eyesight isn't what it was and I
have to peer at the screen to work them out sometimes. I am convinced
there's now something not quite right about this. The numerals /
letters also waver very slightly, but only horizontally. I have been
offered the display board from a breaker 7704A, is it safe to plug it
in and see what happens, or is it not that simple? Thanks gentlemen!
--
Best Regards,
Chris Wilson.
mailto: chris@...
|
Re: A nearly working 7B80 (S/N B058022)
It depends on how enthusiastically the "inker" did the job. Two of my 7B80 have 7 00 inked in the 3 blank fields, but a third one has a blank field followed by a very big 7 across the version fields. The intention will be 670-4177-00 in all cases.
John, did you receive my pictures?
I still don't see what would be wrong in the documentation or in the board IC labeling.
Albert
toggle quoted message
Show quoted text
--- In TekScopes@..., Artekmedia <manuals@...> wrote:
John
Then the board number is likely 670-4177-xx as Albert surmised earlier
But sounds like we are now all looking at the same board overlay regardless
Cheers
Dave
On 7/16/2012 11:46 AM, John Byers wrote:
On 7/16/2012 5:53 AM, Albert wrote:
Hi John,
It's still confusing for me, is "the same results" what you found
before? My board contains 3 ICs (Uxxx), not 2. I will send you
pictures off-line
G'.day Albert
Ive confused you by saying "there are only 2 IC's except for the 20 pin
control chip",
Better I had said "apart from the Tek special 20 pin control chip there
are only two standard type IC;s"
That is, 3x IC's on board. (the control chip, U270 on my drawing, is the
TEK special 20 pin job whose TEK number is part rubbed off, but has an
02 readable at the end, so from parts list (two U270 types stated) would
be a 155-0049-02 (with lockout)), the other one listed ( not on mine)
has an 01 at the end)
and yes, the same results are what I said before,
To Dave: The only part number I see on my board is KE-4598-00
INTERFACE 670-417-7
The board drawing is marked "Interface Circuit Board Assembly 1959-40"
which has "U842" 8 pin minidip outline drawn on the right upper
front of board.behind the trigger mode switches on the rear side
Rgds to all
John
'
.
--
Dave& Lynn Henderson
Manuals@...
www.Artekmedia.com
PO Box 175
Welch,MN 55089
|
Re: A nearly working 7B80 (S/N B058022)
The KE- number should refer back to a drawing. It won't be useful.
The 670-4177 (followed by 2 digits of version number) is the
populated board.
-ls-
John Byers <face1941@...> wrote:
toggle quoted message
Show quoted text
To Dave: The only part number I see on my board is KE-4598-00
INTERFACE 670-417-7
The board drawing is marked "Interface Circuit Board Assembly 1959-40"
which has "U842" 8 pin minidip outline drawn on the right upper
front of board.behind the trigger mode switches on the rear side
Rgds to all
John
'
.
------------------------------------
Yahoo! Groups Links
|
Re: A nearly working 7B80 (S/N B058022)
John
Then the board number is likely 670-4177-xx as Albert surmised
earlier
But sounds like we are now all looking at the same board overlay
regardless
Cheers
Dave
On 7/16/2012 11:46 AM, John Byers wrote:
?
On 7/16/2012 5:53 AM, Albert wrote:
>
> Hi John,
>
> It's still confusing for me, is "the same results"
what you found
> before? My board contains 3 ICs (Uxxx), not 2. I will
send you
> pictures off-line
G'.day Albert
Ive confused you by saying "there are only 2 IC's except
for the 20 pin
control chip",
Better I had said "apart from the Tek special 20 pin
control chip there
are only two standard type IC;s"
That is, 3x IC's on board. (the control chip, U270 on my
drawing, is the
TEK special 20 pin job whose TEK number is part rubbed
off, but has an
02 readable at the end, so from parts list (two U270 types
stated) would
be a 155-0049-02 (with lockout)), the other one listed (
not on mine)
has an 01 at the end)
and yes, the same results are what I said before,
To Dave: The only part number I see on my board is
KE-4598-00
INTERFACE 670-417-7
The board drawing is marked "Interface Circuit Board
Assembly 1959-40"
which has "U842" 8 pin minidip outline drawn on the right
upper
front of board.behind the trigger mode switches on the
rear side
Rgds to all
John
'
.
--
Dave & Lynn Henderson
Manuals@...
PO Box 175
Welch,MN 55089
|
Re: A nearly working 7B80 (S/N B058022)
To Dave and Lyn who asked me what the circuit board details were
The only part number I see on my board is KE-4598-00 INTERFACE 670-417-7
The board drawing is marked "Interface Circuit Board Assembly 1959-40"
which has "U842" 8 pin minidip outline drawn on the right upper front of board.behind the trigger mode switches on the rear side
Rgds
John
|
Re: A nearly working 7B80 (S/N B058022)
On 7/16/2012 5:53 AM, Albert wrote:
Hi John,
It's still confusing for me, is "the same results" what you found
before? My board contains 3 ICs (Uxxx), not 2. I will send you
pictures off-line
G'.day Albert Ive confused you by saying "there are only 2 IC's except for the 20 pin control chip", Better I had said "apart from the Tek special 20 pin control chip there are only two standard type IC;s" That is, 3x IC's on board. (the control chip, U270 on my drawing, is the TEK special 20 pin job whose TEK number is part rubbed off, but has an 02 readable at the end, so from parts list (two U270 types stated) would be a 155-0049-02 (with lockout)), the other one listed ( not on mine) has an 01 at the end) and yes, the same results are what I said before, To Dave: The only part number I see on my board is KE-4598-00 INTERFACE 670-417-7 The board drawing is marked "Interface Circuit Board Assembly 1959-40" which has "U842" 8 pin minidip outline drawn on the right upper front of board.behind the trigger mode switches on the rear side Rgds to all John ' .
|
Re: On ePay: Tektronix 2101 pulse generator, US domestic sale only
David,
my previous posting was a friendly hint for another fellow Tek enthusiastic, who might be interested in the item.
Doing so has a long tradition within this group...
Ciao,
Magnus
|
Re: Help with R7903 needed, some success...
Jim,
The current problem with this guy is something is drawing so much power it causes Q1380 on the main board to blow. Q1381 is okay. When Q1380 goes, it also takes F3488 with it.
toggle quoted message
Show quoted text
On 07/16/2012 10:31 AM, Jim Popwell Jr wrote: what's up mark? I have an sc504 that i had problem with.
mine turned out to be the hv multiplier.
jim
On Jul 16, 2012, at 2:44 AM, Mark Wendt wrote:
On 07/15/2012 12:57 PM, keithostertag wrote:
Good News! We now have a working CRT and R7903!
The Short story: After replacing one resistor the screen came alive. After some adjustments there are two items remaining with this project that I need help with:
1. The readouts only gives one numeral. For instance, .5uS, 5uS, and 50uS all display as 5uS. Similarly, .5V, 5mV, and 50mV all say 5mV. Same for all settings, and regardless which plugins I use. The 10X multiplier makes no difference in the Readout display, though it does make it a little "wavy", like a slight vibration. Also, the Readouts are positioned a little low on the screen, so that the lower ones are half-obscured off the bottom of CRT frame.
2.) I'm going to need a source for some of the push-button switches on the front panel.
The longer story (for those interested):
I was following Albert's suggestion to check the continuity around P1675 when I found pin 3 to TP1883 measured around 5Meg ohms. When I went to touch one side of R1880 in order to lift it, it literally fell apart into two clean pieces. No burn or stress marks of any kind- and nothing else on that board was found bad.
After replacing R1880 the CRT came right up, and I went through both the PS cal as well as the z-axis cal. The are a few sections of the z-axis cal that I can't do (I guess) since I don't have a marker generator. (?)
I want to say that after all these weeks of working on this project I was immensely happy and relieved to see that first trace appear! My guess is that this R7903 had been sitting unused (due to its broken condition) for many years before it got to me. Many caps needed to be replaced on several boards, mostly the PS. Of course I would not have been able to do this without your help and instruction, and I am grateful for your patience and perseverance. Really a good example of group effort!
I know even _less_ about logic circuits than I do analog circuits, so fixing this Readout problem will be very interesting. I am reading the manual...
Your thoughts on how to approach the Readout problem?
Thanks,
Keith Ostertag
Keith,
Congrats on finally getting to the root of the problem. Now, if I could
only have that "Ah Ha!" moment on this damn SC504 I've got. ;-)
Mark
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
|
Re: Tektronix 475 with no display
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.
|
Re: Tektronix 475 with no display
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.
|
Re: Tektronix 475 with no display
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.
|
Re: Tektronix 475 with no display
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.
|
Re: A nearly working 7B80 (S/N B058022)
Sorry, you are right, Stan's book says 670 is with parts indeed.
Albert
toggle quoted message
Show quoted text
--- In TekScopes@..., larrys@... wrote:
A truly bare board is a 388-xxxx-yy. ISTR a 670 is a populated board,
and a 672 is a populated board with any necessary hand adds. If not
that, it's something close.
-ls-
Artekmedia <manuals@...> wrote:
OK that some sense , although I doubt it is a "bare" board, I suspect
the parts in the kit are external to the board, and that the board is
otherwise fully assembled
Dave
On 7/16/2012 8:24 AM, Albert wrote:
Hi Dave,
It seems that 672-0538-00 is a set containing not only the circuit
board but also several other components:
In other words, the bare PCB is not for sale. A 670- is a bare board
says Stan's book.
Albert
There were apparently two different versions of the board
670-4177-xx and 672-0538-xx ( look at the 1st page on your parts list in
the manual)
It is not clear to me looking at my copies of manual which version the
board overlays are for ...but this could explain the differences
Dave All my 7B80s have A1 board 670-4177-00. Actually, 670-417 is etched
and the last 7 is in ink. Probably because the same board cold be
prepared for use in a 7B80 (4177) or a 7B85 (4179 with a 9 in ink).
Albert
Albert & John
What is the part number of your respective boards
Dave
--
Dave& Lynn Henderson
Manuals@
www.Artekmedia.com
PO Box 175
Welch,MN 55089
--
Dave& Lynn Henderson
Manuals@...
www.Artekmedia.com
PO Box 175
Welch,MN 55089
|
David C. Partridge
David Hess