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PSU type compatibility?



 
 
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Old July 16th 16, 01:50 AM posted to alt.comp.hardware
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Default PSU type compatibility?

In article , nobody wrote:

In article , Paul wrote:

wrote:
I know of 5 PC: PSU types, based on the connectors:-

1. with 2 side-by-side, single row sockets that plugged to the
PC single row of pins.
2. with 2-rows of 10 sockets to 20-pins of PC.
3. above "2" plus 2x2=4-way socket yellow-black wired.
4. above "3" plus extra 2x2=4-way socket which can
slot onto 2x10=20-way socket to fit 24-pins of PC.
5. as above "4", but with one-piece 2x12=24-way socket .

I seem to remember that I once ran a PC without the
yellow-black 2x2=4-way socket feeding the 4 pins.
Is that possible?


I believe this 2+2=4 is just an extra/parallel supply for the CPU ?


And then I ran a 24-pin MOBO with a 20-pin PSU?
-- snip --

After a minute, an electolytic capacitor exploded.
Later someone with a fancy PSU tester said the PSU was dud.

My bad description, of placing the 2 statements together?
The exploded-elko is on the MOBO.

What happened?

The 20-sockets PSU had been running the old IDE-only MOBO,
but the 2x2=4-way socket yellow-black hadn't been used.
No MOBO pins.

---
Verify the 2x2 has the wires in the right place ?


The 2x2 is 'keyed' and can't be misconnected?
This 2black+2yellow wires wasn't used in the previous PC, which
worked ok with this PSU.

http://www.playtool.com/pages/psucon...onnectors.html

WoW!! Thanks, nice info.

....
If I get a new PSU, it may be destroyed by the now
destroyed MOBO?

What incremental tests can I do?


In your case, you can:

1) Use an ohmmeter and check the readings between rails.
Is 3.3V shorted to 5V ? Is 5V shorted to 12V ?
Are any of them shorted to ground ? You will need a
lesson from someone, in interpreting dynamic readings.
If the multimeter reading rises and rises, you're charging
a capacitor. That's an example of a response pattern.

2) Open the power supply, and visually figure out which rail
the failed cap was on. Then, when ohming out the motherboard,
you use that information, to select what wires to start
checking for short circuit conditions.

And I measure risk with symptoms. Plenty of people have
a PSU quit, when the OCP or OVP kicks in and the circuit
stops. They can mix and match components at home, and
learn stuff. If a second combination causes the PSU to
quit, that's a data point. There's no explosion.

Whereas, you've had an explosion. That means there is a
definite risk factor, compared to the guy where the PSU
just switched itself off and played dead. If your symptoms
are bad enough, you might never use either item again.
This is your call to make.

And while it may not seem fair, I sometimes recommend
people take their broken kit to a computer shop. And
have it blow up some of their gear. Which is the alternative
if you simply must get the box working again. You can tell
them exactly what happened, so they can weigh the danger
to their collection of scrap equipment. I've not heard
of a computer shop refusing to test something, but there
is always a first time.

And there are certainly "safe" pieces of test gear.
There are professional power supply testers, that
are fully protected. And there are bed of nails
motherboard testers, that can survive insults on
the production line. And if you do manage to
blow one of those, the circuit cards can be
individually removed and replaced. So at the
factory, they "have no fear", because they
have very expensive test equipment.

*******

We can take this supply, and perform a thought experiment on it.

http://www.pavouk.org/hw/en_atxps.html

Look on the right hand side of the diagram. Now, short +5V to
-12V. The 5V circuit has much lower impedance, and it "wins".
It charges C28 to 5V. But, the potential is applied the
wrong way around. C28 is reverse biased. The supply driving
+5V is muscular and won't take no for an answer. C28 explodes.
So if I traced the wire loom on the 20 or 24 pin, saw which
colored wire was joined to that exploded C28, I might start
checking how the -12V wire, got shorted to something with a
more positive potential. On the motherboard end, I check from
-12V to +3.3V, -12V to +5V, looking for signs of a dead short
(a rail-to-rail short, rather than a rail-to-ground short).

Paul
.

Yes I agree with that analysis: driving 5V reversed across a 12V elko
may 'expect' to explode it.

Again, the events we-
The now-damaged MOBO, tested OK on my usual PSU.
Then when I tried to confirm with the PSU of the 486 MOBO, the
elko exploded.

My thinking is:--
The PSU worked with the old/486 PC, where the 4 yellow-black
leads were not used/confirmed, and would not have been detected
if faulty.
First confirm THEORETICALLY that plugging a 20-way connector & the
4 yellow-black connector is OK for a 24-way MOBO?

Yes, I'll trace the exploded elko, to see what rails it's across.

Thanks.




 




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