Update on the dead power supply

  • Thread starter Thread starter Cyde Weys
  • Start date Start date
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Cyde Weys

Just in case anyone was wondering, yes, it was the power supply that
was the component at fault. I've put a new power supply in this
computer and it's working just fine. I also got a multimeter. Is it
possible to test the broken power supply totally isolated, or will I
have to short the green wire and put a load on it again?
 
Cyde said:
Just in case anyone was wondering, yes, it was the power supply that
was the component at fault. I've put a new power supply in this
computer and it's working just fine. I also got a multimeter. Is it
possible to test the broken power supply totally isolated, or will I
have to short the green wire and put a load on it again?
Click to expand...

I took the power supply completely apart and found the cause of its
failure - a huge black scorch mark on the bottom of the circuit board.
It doesn't look like anything that can be fixed (or even if it could,
whether it would be worth it), so I scavenged the power supplies for
parts and threw the rest away.
 
Cyde Weys said:
I took the power supply completely apart and found the
cause of its failure - a huge black scorch mark on the
bottom of the circuit board. It doesn't look like
anything that can be fixed (or even if it could, whether
it would be worth it), so I scavenged the power supplies
for parts and threw the rest away.
Click to expand...

Was it scorched on the side closer to the big capacitors or on the
side closer to where all the wires came out of the PSU? Just
wondering.
 
larrymoencurly said:
Was it scorched on the side closer to the big capacitors or on the
side closer to where all the wires came out of the PSU? Just
wondering.
Click to expand...

It was kind of scorched in the middle, underneath one of the two steel
(or aluminum, not sure) struts that popped out of the middle of the
circuit board. The struts had what looked like transistors (y'know, the
3-wire box thingies) screwed into them, and each strut was attached to
the circuit board by two screws, which went in from underneath. I'm
assuming they were grounding screws because they were that peculiar
green color. Anyway, the scorch mark arced from one of the grounding
screws to somewhere else on the circuit board.

Ahhh, screw it. Here are some pictures. The pictures aren't of
excellent quality, so I worked on them a bit in Photoshop to try to get
the details out.

---
http://terpy.student.umd.edu/images/PSU1.jpg

Here is where you can see the view from the top of the circuit board of
the power supply. Those two screw holes are where the strut attached
to. Those two black rectangles to the right of the holes are
transistors viewed edge-on that screwed into the strut (removed for this
picture, obviously). The black area to the left of the bigger
transistor is NOT a shadow. It is a scorch mark (that originally wasn't
visible until I removed the struts).
---

---
http://terpy.student.umd.edu/images/PSU2.jpg

This shows the bottom of the circuit board from the power supply. The
two screw holes are the same ones as seen from the top view. See those
brown/black scorch marks that travel from the screws upwards, then left,
then down and left, then straight down? I'm not sure what could've
caused that, but it's probably the reason my PSU failed. For what it's
worth, the area of the board where the scorch marks stop is right
underneath where all of the power wires (to PC components) are connected
to the PSU.
---
 
It was kind of scorched in the middle, underneath one of the two steel
(or aluminum, not sure) struts that popped out of the middle of the
circuit board. The struts had what looked like transistors (y'know, the
3-wire box thingies) screwed into them, and each strut was attached to
the circuit board by two screws, which went in from underneath. I'm
assuming they were grounding screws because they were that peculiar
green color. Anyway, the scorch mark arced from one of the grounding
screws to somewhere else on the circuit board.

Ahhh, screw it. Here are some pictures. The pictures aren't of
excellent quality, so I worked on them a bit in Photoshop to try to get
the details out.

---
http://terpy.student.umd.edu/images/PSU1.jpg

Here is where you can see the view from the top of the circuit board of
the power supply. Those two screw holes are where the strut attached
to. Those two black rectangles to the right of the holes are
transistors viewed edge-on that screwed into the strut (removed for this
picture, obviously). The black area to the left of the bigger
transistor is NOT a shadow. It is a scorch mark (that originally wasn't
visible until I removed the struts).
---

---
http://terpy.student.umd.edu/images/PSU2.jpg

This shows the bottom of the circuit board from the power supply. The
two screw holes are the same ones as seen from the top view. See those
brown/black scorch marks that travel from the screws upwards, then left,
then down and left, then straight down? I'm not sure what could've
caused that, but it's probably the reason my PSU failed. For what it's
worth, the area of the board where the scorch marks stop is right
underneath where all of the power wires (to PC components) are connected
to the PSU.
---
Click to expand...

I can't tell a lot from those pictures, but it looks a bit like it was
just overheating the regulator as result of _another_ problem, that the
scorch mark in itself is not a sign of the (primary) problem/failure.

Given the questionable quality of the power supply and the fact that it's
not working anymore I tend to agree with your previous conclusion, that
it's not worth spending any more time on it.
 
Cyde Weys said:
It was kind of scorched in the middle, underneath one of
the two steel (or aluminum, not sure) struts that popped
out of the middle of the circuit board. The struts had
what looked like transistors (y'know, the 3-wire box
thingies) screwed into them, and each strut was attached to
the circuit board by two screws, which went in from underneath.
I'm assuming they were grounding screws because they were
that peculiar green color. Anyway, the scorch mark arced
from one of the grounding screws to somewhere else on the
circuit board.
Click to expand...
Here are some pictures.
Click to expand...
http://terpy.student.umd.edu/images/PSU1.jpg
http://terpy.student.umd.edu/images/PSU2.jpg
Click to expand...

I'm no expert, but I think that a dual diode (3 pins, center pin being
for both cathodes) shorted out, and maybe replacing it and any
electrolytic capacitors connected to it (may have been shorted from
the AC fed to it when the diode failed) would have fixed the PSU. If
the toroid coil was scorched, then any damaged insulation on the
wiring would have to be fixed (pried away from core or other wire and
varnished?). Those struts must be heatsinks, and the screws going
through the transistors and diodes are just to hold them against the
heatsinks, not ground them (there may have been a sheet of grey rubber
between them and the heatsink to isolate them from the heatsink). The
green stuff seems like sealer to keep the screws from working loose.
I'm amazed that you were able to remove the heatsinks without also
unsoldering the diodes and transistors because I've never managed to
do that
 
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