Hello Kerry,
Just a correction...
While the hypothesis of the ¡Â5 stage misbehaving is still sound and would cause exactly the symptoms you describe, I got wrong (and stated wrongly) that the slower timings (slower than 50ns) were derived directly from the 1MHz reference clock. They are not.
All the timings are obtained by division of the 100MHz PLL generated clock.
Still the theory of the ill ¡Â5 divider remains, as it would - at the same time - make the PLLed frequency to be lower (which would directly impact all the time ranges that are BEFORE the ¡Â5 divider) but, since the division factor would be less, all the ranges slower than 50ns (which are divided AFTER the ¡Â5 divider) would remain correct (80MHz ¡Â 4 = 100MHz ¡Â 5).
Rgrds,
Fabio
toggle quoted message
Show quoted text
On Thu, Aug 16, 2018 at 03:02 PM, Fabio Trevisan wrote:
Hello Kerry,
I don't own a TG501 so I don't really qualify as an expert, but I downloaded
the service manual from the Tekwiki (here: )
and, by just looking at the block diagram, it doesn't seem a simple tweak
(e.g., the turn of a trimpot) to change the time marks of 20ns to 25, the 10ns
to 12.5 and 5n to 6.25.
Still, it's technically possible that only the 20n and faster ranges are off,
since all the slower ranges are derived by direct division of the 1MHz
reference clock, while the faster ranges, rely on a 100MHz clock internally
generated by PLLing the 1MHz reference clock, which is divided by 100 (in
successive divisions, ¡Â5, ¡Â2, ¡Â5 and ¡Â2) and phase compared to the
reference 1MHz clock.
If the error is exact (i.e. if the 20ns is turned into exact 25ns) a good
theory could be that something wrong with the 1st stage of dividing by 5
(U310A, U310B and U315A) is making it divide by 4 instead.
This would make the PLL to generate an 80MHz frequency, instead of 100MHz.
First hypothesis that came to my mind was that a decade divider IC could have
been replaced by a binary divider... But not applicable in this case, as the
¡Â5 is obtained by a discrete combination of 3 ECL flip-flops.
My second hypothesis is that, maybe a false contact, (a bad IC socket comes to
mind) is interrupting some signal in this ¡Â5 logic, causing it to misbehave
and divide by 4.
In face of the known issues that some Texas sockets used by Tektronix on the
equipment of this vintage, it's worth to give it a check.
See this link () for more
information on the dreadful Texas IC socket.
If, however, the error is not exact... than it may just be that the PLL is
failing to generate the 100MHz clock.
In this case, it can be easily diagnosed (even with an uncalibrated scope), by
just displaying simultaneously (on 2 channels), the 1MHz reference clock, at
the same time with any of the clocks generated from the - supposed - 100MHz
clock.
If you trigger in one and the other roll on the screen, or vice-versa, than
it's the PLL that it's not locking.
Hope this helps,
Rgrds,
Fabio
On Thu, Aug 16, 2018 at 01:14 PM, <kburns@...> wrote:
Hello
I'm a newcomer to this group who has fairly recently acquired a SG503,
PG506
and TG501 in a TM5003 module. All of these units are working fine, apart
from the TG501 which shows some odd outputs on the 20ns, 10ns and 5ns
markers. The timing seems to be correct on the slower markers (50ns and
below), but the 20ns, 10ns and 5ns show as 25ns, 12.5ns and 6.25ns
respectively. The 2ns is correct (can't check the 1ns, given the bandwidth of
my old Tek 2465A). I've checked the markers on a second scope as well. The
TG501 is a later model (Bo51xxx).
My first thought was that there must be a fault with the 20ns, 10ns and 5ns
outputs - possibly in the dividers - but then wondered if perhaps the
generator had been deliberately modified at some point to give the 25ns,
12.5ns and 6.25ns values. I'm not sure if this mod would be possible with
the TG501? I've had a good look at the manual, but before I start delving
any further I wanted to be sure it is a fault. I have checked the power
supply voltages and ripple and the 1 Mhz oscillator - these are all good.
Any advice on this issue from the experts here would be appreciated.
Thank you
Kerry
|
Hi Leo, I didn't see the photo(s) of your Schaffner AC inlet filter posted, so I put two photos in your photo album of some of the Schaffner filters I have that were taken out of some 22xx scopes. /g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0 Some of them have an extra tag on the side with that 'FUY 1651' on them, but others have no extra tag on them. I have more of these Schaffner filters I've removed, but they are all the same. I think those two X or Y caps in the black filter box on the back wall of the scope are the only other X or Y caps in your 2215A besides C904 on the mainboard. There was a circuit modification done to that black box where two components get their positions in the circuit switched. I've done this modification several times, but I wonder if it is worth doing. All of this is described in the instructions for the Mod Kit 050-2242-03 which is available at: hakanh.com/dl/docs/kitinstructions/050-2242-03.pdf A few years back I also made a document that relates to all of this, it's not posted anywhere that I know of, so I will send it to you directly. It turns out that you can not put anything but "image" files in your photo album/ tom jobe...
On 8/16/2018 9:05 AM, satbeginner wrote: On Thu, Aug 16, 2018 at 03:43 PM, tom jobe wrote:
Hi Leo,
Thanks for the progress report, It's good to see that your 2215A repairs
so far have gone well!
In studying your photos, it looks like you have one of those dreaded
"Schaffner" brand AC inlet filters (where the AC cord plugs into the
back of the scope).
If that is what you have, they have a poor reliability record when used
on 240 AC line voltage, if you also have that too.
I'm in a 120 volt AC part of the world and I started changing them after
having just one scary "Schaffner" failure.
The Tekscopes message archive should have some "Schaffner" discussions
from the past, and a Google search on the term 'Schaffner filter
failure' will get you more information too.
You might also consider changing the few X and Y caps in the 2215A,
especially C904 which is under the AC inlet filter and behind the main
power switch.
C904 is much easier to change while you have the AC inlet filter removed.
The original X and Y capacitors have difficulty with 240 volt mains, so
you might want to get the highest rated replacements you can find.
tom jobe...
On 8/16/2018 4:19 AM, satbeginner wrote:
Hi all,
just a final message: it's all done!
Today I received the 12V 60mm brushless fan that was a perfect fit.
I used the half wave rectifier circuit I was able to place the components for on the board, the fan is running nicely without real noise on 9V.
I mean, you can hear it, but only just.
There are plenty perforations all around the casing to let cool air in, so I choose to have it blowing out, so it is sucking the warm air from the inside
of the scope and remove it from the scope.
(Like in my 2465's)
One extra thing I found: When I put all the covers back and ran the scope for a while, I found that the one screw on the right hand side is actually
quite important.
This creates a thermal connection between where the internal heatsink is and the outside blue cabinet, so that way the scope's casing helps in cooling the
scope too.
Again, pictures are here: /g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0
Un saludo,
Leo
Hi Tom,
As it turns out, it is not yet solved... ;-)
Yes, I opened the scope again, and yes, it's a Schaffner line-filter.
I put a picture of it in the album: /g/TekScopes/album?id=64919
Is this one of the "explosive" types?? If so, I'll will replace it.
Although this scope spend his whole life in The Netherlands,, so maybe it OK?
Further down the line there is this black, plastic box that contains another line-filter.
In there are two 2n2 RIFA capacitors (similar as in the 2465 PS), they already look "cracked", so I will replace them too.
To be continued,
Leo
|
Hello Kerry,
I don't own a TG501 so I don't really qualify as an expert, but I downloaded the service manual from the Tekwiki (here: ) and, by just looking at the block diagram, it doesn't seem a simple tweak (e.g., the turn of a trimpot) to change the time marks of 20ns to 25, the 10ns to 12.5 and 5n to 6.25.
Still, it's technically possible that only the 20n and faster ranges are off, since all the slower ranges are derived by direct division of the 1MHz reference clock, while the faster ranges, rely on a 100MHz clock internally generated by PLLing the 1MHz reference clock, which is divided by 100 (in successive divisions, ¡Â5, ¡Â2, ¡Â5 and ¡Â2) and phase compared to the reference 1MHz clock.
If the error is exact (i.e. if the 20ns is turned into exact 25ns) a good theory could be that something wrong with the 1st stage of dividing by 5 (U310A, U310B and U315A) is making it divide by 4 instead.
This would make the PLL to generate an 80MHz frequency, instead of 100MHz.
First hypothesis that came to my mind was that a decade divider IC could have been replaced by a binary divider... But not applicable in this case, as the ¡Â5 is obtained by a discrete combination of 3 ECL flip-flops.
My second hypothesis is that, maybe a false contact, (a bad IC socket comes to mind) is interrupting some signal in this ¡Â5 logic, causing it to misbehave and divide by 4.
In face of the known issues that some Texas sockets used by Tektronix on the equipment of this vintage, it's worth to give it a check.
See this link () for more information on the dreadful Texas IC socket.
If, however, the error is not exact... than it may just be that the PLL is failing to generate the 100MHz clock.
In this case, it can be easily diagnosed (even with an uncalibrated scope), by just displaying simultaneously (on 2 channels), the 1MHz reference clock, at the same time with any of the clocks generated from the - supposed - 100MHz clock.
If you trigger in one and the other roll on the screen, or vice-versa, than it's the PLL that it's not locking.
Hope this helps,
Rgrds,
Fabio
toggle quoted message
Show quoted text
On Thu, Aug 16, 2018 at 01:14 PM, <kburns@...> wrote:
Hello
I'm a newcomer to this group who has fairly recently acquired a SG503, PG506
and TG501 in a TM5003 module. All of these units are working fine, apart
from the TG501 which shows some odd outputs on the 20ns, 10ns and 5ns
markers. The timing seems to be correct on the slower markers (50ns and
below), but the 20ns, 10ns and 5ns show as 25ns, 12.5ns and 6.25ns
respectively. The 2ns is correct (can't check the 1ns, given the bandwidth of
my old Tek 2465A). I've checked the markers on a second scope as well. The
TG501 is a later model (Bo51xxx).
My first thought was that there must be a fault with the 20ns, 10ns and 5ns
outputs - possibly in the dividers - but then wondered if perhaps the
generator had been deliberately modified at some point to give the 25ns,
12.5ns and 6.25ns values. I'm not sure if this mod would be possible with
the TG501? I've had a good look at the manual, but before I start delving
any further I wanted to be sure it is a fault. I have checked the power
supply voltages and ripple and the 1 Mhz oscillator - these are all good.
Any advice on this issue from the experts here would be appreciated.
Thank you
Kerry
|
Hi Tom and others, Sorry for my mistake of changing the subject, I have messed-up, so there are two threads now, I promise to not do that again... :-( Anyway, I added a picture of the two RIFA capacitors and the Schaffner filter I replaced in the scope here: /g/TekScopes/album?id=64919This should help to avoid nasty surprises in the (near?) future. However, one question did pop up when checking the settings again: Earlier, during calibration, on the attenuatorboard I found the double trim capacitors for the 10x and 100x attenuator HF compensation a bit "sensitive" to rotation and/or pressing in? Is this a know issue with these, and is known what's inside of them?? Un saludo, Leo
|
Re: tektronix 214 option 94
Hi Miguel,
That is definitely an odd number for an option. Up until now I would have said options are ALWAYS listed in the catalogs as opposed to modifications which are never listed. But I just checked the 1983 catalog and the only options are 01 and 02 and they relate to different mains power for use in foreign countries. Does your 214 have an unusual power plug?
I just checked my 214 and it has no options. My option "insert" is blank.
Dennis Tillman W7PF
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Show quoted text
-----Original Message-----
From: Miguel Work
Sent: Thursday, August 16, 2018 2:25 AM
Subject: [TekScopes] tektronix 214 option 94
Which is optino 94 for a Tektronix 214? -- Dennis Tillman W7PF TekScopes Moderator
|
Hello
I'm a newcomer to this group who has fairly recently acquired a SG503, PG506 and TG501 in a TM5003 module. All of these units are working fine, apart from the TG501 which shows some odd outputs on the 20ns, 10ns and 5ns markers. The timing seems to be correct on the slower markers (50ns and below), but the 20ns, 10ns and 5ns show as 25ns, 12.5ns and 6.25ns respectively. The 2ns is correct (can't check the 1ns, given the bandwidth of my old Tek 2465A). I've checked the markers on a second scope as well. The TG501 is a later model (Bo51xxx).
My first thought was that there must be a fault with the 20ns, 10ns and 5ns outputs - possibly in the dividers - but then wondered if perhaps the generator had been deliberately modified at some point to give the 25ns, 12.5ns and 6.25ns values. I'm not sure if this mod would be possible with the TG501? I've had a good look at the manual, but before I start delving any further I wanted to be sure it is a fault. I have checked the power supply voltages and ripple and the 1 Mhz oscillator - these are all good.
Any advice on this issue from the experts here would be appreciated.
Thank you
Kerry
|
On Thu, Aug 16, 2018 at 03:43 PM, tom jobe wrote:
Hi Leo,
Thanks for the progress report, It's good to see that your 2215A repairs
so far have gone well!
In studying your photos, it looks like you have one of those dreaded
"Schaffner" brand AC inlet filters (where the AC cord plugs into the
back of the scope).
If that is what you have, they have a poor reliability record when used
on 240 AC line voltage, if you also have that too.
I'm in a 120 volt AC part of the world and I started changing them after
having just one scary "Schaffner" failure.
The Tekscopes message archive should have some "Schaffner" discussions
from the past, and a Google search on the term 'Schaffner filter
failure' will get you more information too.
You might also consider changing the few X and Y caps in the 2215A,
especially C904 which is under the AC inlet filter and behind the main
power switch.
C904 is much easier to change while you have the AC inlet filter removed.
The original X and Y capacitors have difficulty with 240 volt mains, so
you might want to get the highest rated replacements you can find.
tom jobe...
On 8/16/2018 4:19 AM, satbeginner wrote:
Hi all,
just a final message: it's all done!
Today I received the 12V 60mm brushless fan that was a perfect fit.
I used the half wave rectifier circuit I was able to place the components for on the board, the fan is running nicely without real noise on 9V.
I mean, you can hear it, but only just.
There are plenty perforations all around the casing to let cool air in, so I choose to have it blowing out, so it is sucking the warm air from the inside
of the scope and remove it from the scope.
(Like in my 2465's)
One extra thing I found: When I put all the covers back and ran the scope for a while, I found that the one screw on the right hand side is actually
quite important.
This creates a thermal connection between where the internal heatsink is and the outside blue cabinet, so that way the scope's casing helps in cooling the
scope too.
Again, pictures are here:
/g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0
Un saludo,
Leo
Hi Tom, As it turns out, it is not yet solved... ;-) Yes, I opened the scope again, and yes, it's a Schaffner line-filter. I put a picture of it in the album: /g/TekScopes/album?id=64919Is this one of the "explosive" types?? If so, I'll will replace it. Although this scope spend his whole life in The Netherlands,, so maybe it OK? Further down the line there is this black, plastic box that contains another line-filter. In there are two 2n2 RIFA capacitors (similar as in the 2465 PS), they already look "cracked", so I will replace them too. To be continued, Leo
|
Re: 2215A LVPS repair [Solved]
Hi Leo,
Thanks for the progress report, It's good to see that your 2215A repairs so far have gone well!
In studying your photos, it looks like you have one of those dreaded "Schaffner" brand AC inlet filters (where the AC cord plugs into the back of the scope).
If that is what you have, they have a poor reliability record when used on 240 AC line voltage, if you also have that too.
I'm in a 120 volt AC part of the world and I started changing them after having just one scary "Schaffner" failure.
The Tekscopes message archive should have some "Schaffner" discussions from the past, and a Google search on the term 'Schaffner filter failure' will get you more information too.
You might also consider changing the few X and Y caps in the 2215A, especially C904 which is under the AC inlet filter and behind the main power switch.
C904 is much easier to change while you have the AC inlet filter removed.
The original X and Y capacitors have difficulty with 240 volt mains, so you might want to get the highest rated replacements you can find.
tom jobe...
toggle quoted message
Show quoted text
On 8/16/2018 4:19 AM, satbeginner wrote: Hi all,
just a final message: it's all done!
Today I received the 12V 60mm brushless fan that was a perfect fit.
I used the half wave rectifier circuit I was able to place the components for on the board, the fan is running nicely without real noise on 9V.
I mean, you can hear it, but only just.
There are plenty perforations all around the casing to let cool air in, so I choose to have it blowing out, so it is sucking the warm air from the inside of the scope and remove it from the scope.
(Like in my 2465's)
One extra thing I found: When I put all the covers back and ran the scope for a while, I found that the one screw on the right hand side is actually quite important.
This creates a thermal connection between where the internal heatsink is and the outside blue cabinet, so that way the scope's casing helps in cooling the scope too.
Again, pictures are here: /g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0
Un saludo,
Leo
|
On Thu, 16 Aug 2018 06:05:57 +0200, you wrote: Hello Folks,
Thanks for all thoses interestings comments.
As Ive reconnected the ground, and turned power ON : no differential
main shut down occur, even when my finger
played with chassis parts. I also mesured voltage between ground and
chassis : close to zero -- few mV-..
The idea to use the same wall socket to avoid ground loop is fine.
Question : sometime when troubleshooting radios, I use a ground lead
between scope and radio to avoid using probe's aligator clip.
What do you think about ? can I introduce false mesurements ? Yes and no. The ground lead for the probe, when properly attached, minimizes ringing on the signal. The long lead from chassis to chassis will not. For low frequency signals (especially sine waves), you're not likely to see much of a difference. Go play digital, and you will. The length of the probe's ground lead and where it is placed also have an effect, especially if you've got a different ground potential (by millivolts) across a PC board or a chassis. Harvey
Regards
Alain
Le 15.08.2018 ¨¤ 20:40, Richard Knoppow a ¨¦crit?:
??? A hot chassis can also be caused by RF filter capacitors connected
from each side of the line to the chassis. I would be much more
suspicious of these if they exist in the 453 than of the electrostatic
shield in the power transformer. If there are such caps in the 453
lift them to see if the voltage on the chassis disappears. You might
want to replace them. There are special capacitors for this service
which fail open so they don't connect the line directly to the chassis.
??? The voltage on the chassis will depend on the amount of
capacitance and the impedance of the measuring device.
??? You can always generate a long argument by discussing the
differences between lightening protection grounds, power line safety
grounds and grounds to eliminate common impedances in AF and RF circuits.
On 8/15/2018 1:52 AM, Craig Sawyers wrote:
That would be typical if the chassis is ungrounded. Capacitance
between the primary and shield (which
is connected to the chassis) in the mains transformer will cause
this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous
thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope
safe first.
Craig
|
Re: 2215A LVPS repair [Solved]
Hi all, just a final message: it's all done! Today I received the 12V 60mm brushless fan that was a perfect fit. I used the half wave rectifier circuit I was able to place the components for on the board, the fan is running nicely without real noise on 9V. I mean, you can hear it, but only just. There are plenty perforations all around the casing to let cool air in, so I choose to have it blowing out, so it is sucking the warm air from the inside of the scope and remove it from the scope. (Like in my 2465's) One extra thing I found: When I put all the covers back and ran the scope for a while, I found that the one screw on the right hand side is actually quite important. This creates a thermal connection between where the internal heatsink is and the outside blue cabinet, so that way the scope's casing helps in cooling the scope too. Again, pictures are here: /g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0 Un saludo, Leo
|
|
|
Hi Jennifer,
It is appropriate to let the members of TekScopes know if you have any conflict of interest when you post an item for sale.
Dennis Tillman W7PF
toggle quoted message
Show quoted text
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Jennifer McCubbins
Sent: Wednesday, August 15, 2018 7:16 PM
To: [email protected]
Subject: [TekScopes] Tek scope
%2Fitm%2F362410334858 -- Dennis Tillman W7PF TekScopes Moderator
|
Re: Resurrecting a 475 - Request for Guidance
On 15/08/18 23:25, JR wrote: Regarding the removal of the two attenuator boards/assemblies, is the best way to get at the nuts holding them to the front panel with a small spanner? I'm having a little difficulty getting them free. See
|
|
|
Yes, for best frequency response the ground lead should be short and
the area between it and the probe minimal.
You may see ringing and other strange stuff with your separate ground lead.
Probably OK for a rough check of supply voltages or slow signals, but
definitely no use for ripple and noise measurements (in those cases
sometimes even the supplied alligator leads are just too long).
You need to think about what you are measuring and adapt accordingly.
Using the absolute best setup all the time is also completely impractical.
ST
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Show quoted text
On Thu, Aug 16, 2018 at 6:05 AM, F4GNY <f4gny@...> wrote: Question : sometime when troubleshooting radios, I use a ground lead
between scope and radio to avoid using probe's aligator clip.
What do you think about ? can I introduce false mesurements ?
Regards
Alain
|
Hello Folks,
Thanks for all thoses interestings comments.
As Ive reconnected the ground, and turned power ON : no differential
main shut down occur, even when my finger
played with chassis parts. I also mesured voltage between ground and
chassis : close to zero -- few mV-..
The idea to use the same wall socket to avoid ground loop is fine.
Question : sometime when troubleshooting radios, I use a ground lead
between scope and radio to avoid using probe's aligator clip.
What do you think about ? can I introduce false mesurements ?
Regards
Alain
toggle quoted message
Show quoted text
Le 15.08.2018 ¨¤ 20:40, Richard Knoppow a ¨¦crit?: ??? A hot chassis can also be caused by RF filter capacitors connected
from each side of the line to the chassis. I would be much more
suspicious of these if they exist in the 453 than of the electrostatic
shield in the power transformer. If there are such caps in the 453
lift them to see if the voltage on the chassis disappears. You might
want to replace them. There are special capacitors for this service
which fail open so they don't connect the line directly to the chassis.
??? The voltage on the chassis will depend on the amount of
capacitance and the impedance of the measuring device.
??? You can always generate a long argument by discussing the
differences between lightening protection grounds, power line safety
grounds and grounds to eliminate common impedances in AF and RF circuits.
On 8/15/2018 1:52 AM, Craig Sawyers wrote:
That would be typical if the chassis is ungrounded. Capacitance
between the primary and shield (which
is connected to the chassis) in the mains transformer will cause
this. First thing to do is connect
the ground in the mains plug - the previous user did a dangerous
thing by disconnecting the ground.
There may be other problems to solve, of course - but make the scope
safe first.
Craig
|
Well, after a week on vacation, I replaced the old 18,000 uF, 16 V C821
with a new 22,000 uF, 25 V job that was the same diameter but less than
half the length. I knew I was going to be out of town, so I ordered
from Digi-Key just before I left, and the caps (I bought 2, just in
case) arrived just before I got back. After removing the old cap by
sawing off 2 of the leads right next to the edge of the rectifier board
with a hacksaw blade and a utility knife, I was able to mop up the
solder from the other 3 leads with generous use of rosin flux and large
solder braid.
The new cap's leads didn't quite match up with the holes, so I added a
piece of 22 gauge wire from one. And... shorted it out on the underside
of the board! D'oh! Tried again with the one lead with the wire on it
cut down to size and covered with Kapton and electrical tape. Voila,
that did it! 5 V rail is clean now. Still a bit of ripple on all
supplies, particularly 15 V, but good enough for now. The 7603 is back
to life and triggering on millivolt signals no problem.
Thanks everybody for your help!
Next project is replacing the backup battery (also purchased from D-K at
the same time as the caps) in my HP 8566 spectrum analyzer, but that is
a story for another group. And at some point I'll want to try to fix my
botched job replacing a CMOS battery on my Tek TLA711 logic analyzer.
If I don't get very far with that job, I'll ask here, unless there is a
Tek logic analyzers group.
Jim
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Show quoted text
------ Original Message ------ From: "Craig Sawyers" <c.sawyers@...> To: [email protected]Sent: 7/21/2018 11:43:55 PM Subject: Re: [TekScopes] Dead 7603 BTW, I did try a 7A22, a 7A26, and a 7B85 in the plug-in slots last
night. Readout was a bit
grainy, and it
was impossible to get a stable trigger on the calibration squarewave
except at the highest
amplitude, a
few volts. Since the 7B80/85 use +5V it is not surprising that they don't work
properly if your 5V is screwy.
Craig
--- This email has been checked for viruses by AVG.
|
Re: Resurrecting a 475 - Request for Guidance
On Aug 15, 2018, at 7:35 PM, Tom Miller <tmiller11147@... <mailto:tmiller11147@...>> wrote:
Look for a tantalum with a small hole in it. Our work benches vary quite a lot, and things found useful by some may not even be at others places: I have a relaltively common magnifying goose-neck lamp. The tubular fluorescent lamp surround a magnifying lens of about 3-1/3 or 4 inches diameter. This thing is very useful for some work, such as finding a tantalum cap with a hole in one end. Other folks use magnifying ¡°goggles¡± - I suspect these are more useful than the lamp with magnifier for some things. Roy Morgan k1lky68@... <mailto:k1lky68@...>
|
Re: Resurrecting a 475 - Request for Guidance
Hi John,
It's good to hear that you are making progress on your 475.
Those large capacitors for the low voltage supplies in the aluminum cans often fail internally and do not show any bulging or other obvious failure.
When you find a large ripple on one of the low voltage supplies and take that capacitor apart, you will often see one of the connections to the outside has corroded and completely disconnected the capacitor internally.
Work on whatever seems to be the biggest problem you see and you will gradually get it all fixed.
I have not worked on a 4xx scope in a very long time so have no idea about how things come apart.
tom jobe...
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Show quoted text
On 8/15/2018 3:25 PM, JR wrote: It turns out that C965 (Board A9), a tantalum bypass capacitor on the +15 rail had gone bad; removing brought the +15 rail resistance to ground back to where it should be. Most of the capacitors look to be in pretty good condition; I have not come across any bulges, deformities, leaked electrolyte or burn marks on any of them, even the larger axial lead supply capacitors.
I powered it on, and checked the supply voltages at the test points; all were within specification, although I haven't checked the ripple on each yet. I haven't checked any of the high voltage test points yet, as I'm currently lacking the equipment to do so safely.
A couple minutes into testing the powered on scope (I couldn't find the test point for +105/160), some other component let go, with a loud pop, accompanied by a whistling sound and small quantity of smoke. So, the hunt is on for the culprit. I have removed boards A3, A7 and A8 so far, and have found no obviously failed components on any of them. I thought at first that something on A7 (timing board) failed, given the location where the smoke seemed to come from, but that doesn't seem to be the case. Is there any component in the recess along with the CRT known to fail in such a way?
Interestingly, after the component failure, all the supply voltages were still within specification.
Regarding the removal of the two attenuator boards/assemblies, is the best way to get at the nuts holding them to the front panel with a small spanner? I'm having a little difficulty getting them free.
Thanks,
John
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Re: Resurrecting a 475 - Request for Guidance
On Wed, 15 Aug 2018 15:25:30 -0700, you wrote: It turns out that C965 (Board A9), a tantalum bypass capacitor on the +15 rail had gone bad; removing brought the +15 rail resistance to ground back to where it should be. Most of the capacitors look to be in pretty good condition; I have not come across any bulges, deformities, leaked electrolyte or burn marks on any of them, even the larger axial lead supply capacitors.
I powered it on, and checked the supply voltages at the test points; all were within specification, although I haven't checked the ripple on each yet. I haven't checked any of the high voltage test points yet, as I'm currently lacking the equipment to do so safely.
A couple minutes into testing the powered on scope (I couldn't find the test point for +105/160), some other component let go, with a loud pop, accompanied by a whistling sound and small quantity of smoke. So, the hunt is on for the culprit. I have removed boards A3, A7 and A8 so far, and have found no obviously failed components on any of them. I thought at first that something on A7 (timing board) failed, given the location where the smoke seemed to come from, but that doesn't seem to be the case. Is there any component in the recess along with the CRT known to fail in such a way? Look for the capacitors across the AC line in the power filter. They can fail, especially if you're in an environment that uses a 220 volt (nominal) line voltage. The value of nominal has been increasing over the years, and will bite you. Harvey
Interestingly, after the component failure, all the supply voltages were still within specification.
Regarding the removal of the two attenuator boards/assemblies, is the best way to get at the nuts holding them to the front panel with a small spanner? I'm having a little difficulty getting them free.
Thanks,
John
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Fabio Trevisan
satbeginner