From Newsgroup: sci.electronics.repair

Jake Tanenbum <ez8799ne@aolnospam.net> wrote:

I am currently trying to repair an old Dell PS-6371-1DF2-1F PSU that had failed in a Dell desktop. Opening the unit and, after discharging the
main caps, I note about four electrolytics with domed tops and I suspect these need replacement. I was going to try testing them in circuit with
an ESR tester, but the components are so close that I can't really tell where the capacitor traces are on the solder side. What are recommended simple ways that I can match the top component side with the bottom side traces when no manual is available? Trying to eyeball and guess where
each trace and component match are isn't going to get me very far.

I'm not sure there are general rules, but some things to know are that some larger caps have leads that snap into the PCB rather than wires. You can
spot the soldered snaps because the points aren't perpendicular to the
board.

Also you know that the caps have two legs and that there will usually be no other through-hole components under the cap body. So you're looking for circles clear of through-hole leads in which there are two equally-sized through-hole solder joints equidistant from the centre of the circle, on opposite sides.

Plus typically big electrolytics are on power rails so I would be looking
for wide tracks which carry the current and relatively large solder joints. (although on 4+ layer boards caps could be soldered to power planes inside
the board instead, so wide tracks might not be visible on the surface)

Another thing that can help is to take a photo of the solder side, mirror it
in software and print it out. Place it next to the component side of the
board and you can soon start to work out which leads are coming from which components. If you mark the leads you've identified on the photo you can
then identify others by a process of elimination.

Theo
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From Newsgroup: sci.electronics.repair

On Sun, 3 May 2026 14:38:26 -0400, Jake Tanenbum
<ez8799ne@aolnospam.net> wrote:

I am currently trying to repair an old Dell PS-6371-1DF2-1F PSU that had >failed in a Dell desktop. Opening the unit and, after discharging the
main caps, I note about four electrolytics with domed tops and I suspect >these need replacement. I was going to try testing them in circuit with
an ESR tester, but the components are so close that I can't really tell >where the capacitor traces are on the solder side. What are recommended >simple ways that I can match the top component side with the bottom side >traces when no manual is available? Trying to eyeball and guess where
each trace and component match are isn't going to get me very far.

Thank you in advance.

Jake T

If the caps have a dome for a top, they're defective. Replace them
with 105#C equivalents.

The only way you're going to get easy access to the solder side of the
PCB is to remove the sheet metal case. If you can't locate the
capacitors from the solder side of the board, shine a flashlight
through the PCB, from the components side of the PCB. That will
produce a shadow of the case.

Another way is to take a photograph of the components side. Use some
photo editor to reduce the size of the image so that it's actual size
(1:1). I use Irfanview:
<https://www.irfanview.com>
Reverse the image. Print the image actual size (1:1). Lay the print
over the component side. You should have something resembling a
component and trace outline. If the leads are long enough, you can
push them through the paper. That will expose the component leads so
they can be probed with an ESR meter.

Maybe get a replacement used power supply: <https://www.ebay.com/sch/i.html?_nkw=%20Dell%20PS-6371-1DF2-1F>
The risk here is that the replacement used power supply might be as
old as yours (about 20 years) and might also be full of almost dead
capacitors.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272 AE6KS 831-336-2558

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From Newsgroup: sci.electronics.repair

On 5/3/26 6:45 PM, Jeff Liebermann wrote:

On Sun, 3 May 2026 14:38:26 -0400, Jake Tanenbum
<ez8799ne@aolnospam.net> wrote:

I am currently trying to repair an old Dell PS-6371-1DF2-1F PSU that had
failed in a Dell desktop. Opening the unit and, after discharging the
main caps, I note about four electrolytics with domed tops and I suspect
these need replacement. I was going to try testing them in circuit with
an ESR tester, but the components are so close that I can't really tell
where the capacitor traces are on the solder side. What are recommended
simple ways that I can match the top component side with the bottom side
traces when no manual is available? Trying to eyeball and guess where
each trace and component match are isn't going to get me very far.

Thank you in advance.

Jake T

If the caps have a dome for a top, they're defective. Replace them
with 105-#C equivalents.

Four are domed, but I am going to replace some near the domed ones as
well.

The only way you're going to get easy access to the solder side of the
PCB is to remove the sheet metal case. If you can't locate the
capacitors from the solder side of the board, shine a flashlight
through the PCB, from the components side of the PCB. That will
produce a shadow of the case.

I think the board was a little too thick and/or I couldn't get the
flashlight or work light close enough (tried both).

Another way is to take a photograph of the components side. Use some
photo editor to reduce the size of the image so that it's actual size
(1:1). I use Irfanview:
<https://www.irfanview.com>
Reverse the image. Print the image actual size (1:1). Lay the print
over the component side. You should have something resembling a
component and trace outline. If the leads are long enough, you can
push them through the paper. That will expose the component leads so
they can be probed with an ESR meter.

I was able to use my flat bed scanner to scan both sides of the board.
The component side didn't scan all that well as I think there was too
much spacing caused by the components that separated the circuit board
from the scanning surface to too great of an extent. However, with
enough fiddling in Affinity Photo, my photo editor, I think I was able
to get the alignment close enough to know where the caps are from the
solder side.

Maybe get a replacement used power supply: <https://www.ebay.com/sch/i.html?_nkw=%20Dell%20PS-6371-1DF2-1F>
The risk here is that the replacement used power supply might be as
old as yours (about 20 years) and might also be full of almost dead capacitors.

Thanks for the suggestion, but those are as expensive as more modern
lower end 80 plus ones. I'd probably go with a lightly used and recent
80 plus as replacement if I go that route.
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From Newsgroup: sci.electronics.repair

On Sun, 3 May 2026 20:53:27 -0400, Jake Tanenbum
<ez8799ne@aolnospam.net> wrote:

On 5/3/26 6:45 PM, Jeff Liebermann wrote:

On Sun, 3 May 2026 14:38:26 -0400, Jake Tanenbum
<ez8799ne@aolnospam.net> wrote:

I am currently trying to repair an old Dell PS-6371-1DF2-1F PSU that had >>> failed in a Dell desktop. Opening the unit and, after discharging the
main caps, I note about four electrolytics with domed tops and I suspect >>> these need replacement. I was going to try testing them in circuit with >>> an ESR tester, but the components are so close that I can't really tell
where the capacitor traces are on the solder side. What are recommended >>> simple ways that I can match the top component side with the bottom side >>> traces when no manual is available? Trying to eyeball and guess where
each trace and component match are isn't going to get me very far.

Thank you in advance.

Jake T

If the caps have a dome for a top, they're defective. Replace them
with 105#C equivalents.

Four are domed, but I am going to replace some near the domed ones as
well.

Visual bulging of the electrolytic capacitors is NOT going to identify
all the failing capacitors. The physically smaller electrolytic
capacitors do not produce domes. Instead they leak liquid electrolyte
which appears as a brown tar on the PCB around the base of the
capacitor. Some smaller electrolytics blow the rubber plug out of the
bottom of the capacitor. Some show no visible indication of a
problem. Fortunately, an ESR tester will usually show a problem.
Since you now have the power supply disassembled, you might as well
test every electrolytic capacitor. When I was still repairing power
supplies, it was not unusual for me to find a power supply with almost
every electrolytic capacitor exhibiting high ESR measurements. When
in doubt, replace everything that exhibits high ESR.

Incidentally, I have three ESR testers. When I started finding boards
with all the electrolytics appearing to be defective, I began
mis-trusting my initial ESR tester: <https://zilogbob.com/esr_meter/esrhints.htm>
So, I purchased some others:
<https://www.midwestdevices.com> <https://www.electronics-diy.com/esr-meter.php>
After some modifications, my original ESR meter, from Bob Parker,
proved to be the best.

The only way you're going to get easy access to the solder side of the
PCB is to remove the sheet metal case. If you can't locate the
capacitors from the solder side of the board, shine a flashlight
through the PCB, from the components side of the PCB. That will
produce a shadow of the case.

I think the board was a little too thick and/or I couldn't get the >flashlight or work light close enough (tried both).

It works well with G10 PCB material and not so well with cheaper
phenolic.

Another way is to take a photograph of the components side. Use some
photo editor to reduce the size of the image so that it's actual size
(1:1). I use Irfanview:
<https://www.irfanview.com>
Reverse the image. Print the image actual size (1:1). Lay the print
over the component side. You should have something resembling a
component and trace outline. If the leads are long enough, you can
push them through the paper. That will expose the component leads so
they can be probed with an ESR meter.

I was able to use my flat bed scanner to scan both sides of the board.
The component side didn't scan all that well as I think there was too
much spacing caused by the components that separated the circuit board
from the scanning surface to too great of an extent.

Agreed. Using a scanner as a camera is limited by the scanner's depth
of field. A scanner is in focus only when the item being copied is
directly in contact with the glass. At best, you might have 1/4 inch
of depth after which everything is out of focus. Digital cameras,
cell phone cameras and USB cameras have the same problem. You can
increase the depth of field if you stop down to a small f-number
(focal-length / aperture-diameter) which requires using rather bright
lights. That's why photo studios use big bright lights.

However, with
enough fiddling in Affinity Photo, my photo editor, I think I was able
to get the alignment close enough to know where the caps are from the
solder side.

This one?
<https://www.affinity.studio/photo-editing-software>
I don't do much photo editing and Affinity would be overkill for me.

Maybe get a replacement used power supply:
<https://www.ebay.com/sch/i.html?_nkw=%20Dell%20PS-6371-1DF2-1F>
The risk here is that the replacement used power supply might be as
old as yours (about 20 years) and might also be full of almost dead
capacitors.

Thanks for the suggestion, but those are as expensive as more modern
lower end 80 plus ones. I'd probably go with a lightly used and recent
80 plus as replacement if I go that route.

You didn't include your parts and repair time in your calculation. Of
course a modern power supply would be better than a 20 year old used
power supply.

I'm not sure what manner of computer case you're using, but the older
Compaq tower cases required some rather long 12V/5V power cables.
That's why I suggested an identical replacement (with long leads)
instead of a modern power supply.
--
Jeff Liebermann jeffl@cruzio.com
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272 AE6KS 831-336-2558

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