Hello!

I have a problem with my Optiplex 745 power supply, model H275P-01.

I printed out the ATX 24 pin pinout and whats odd is when I short the
pins to turn the unit on, its turns on ok.

I read the voltages out and I get what is in spec when not plugged
in...

However, WHEN i plug in just the ATX aux 4 pin connector (for the chip
extra power) the power supply works fine, but when I plug in the main
24 pin connector it stops....

My questions:

Do you think the power supply needs recap or the motherboard is at
fault here?

I opened the power supply but didn't see any leaky caps...

I thought it would be more obvious which caps are bad but it looks
like i might just have to recap the whole supply!

What would cause the power supply to run fine when not plugged in, and
give the right volts out, but not work when plugged in?

I assume its some bad caps in the supply itself but thought I would
ask on here to see if any one has dealt with somethig like this before.

On 1 ene, 15:53, n8ball wrote:
Hello!

I have a problem with my Optiplex 745 power supply, model H275P-01.

I printed out the ATX 24 pin pinout and whats odd is when I short the
pins to turn the unit on, its turns on ok.

I read the voltages out and I get what is in spec when not plugged
in...

However, WHEN i plug in just the ATX aux 4 pin connector (for the chip
extra power) the power supply works fine, but when I plug in the main
24 pin connector it stops....

My questions:

Do you think the power supply needs recap or the motherboard is at
fault here?

I opened the power supply but didn't see any leaky caps...

I thought it would be more obvious which caps are bad but it looks
like i might just have to recap the whole supply!

What would cause the power supply to run fine when not plugged in, and
give the right volts out, but not work when plugged in?

I assume its some bad caps in the supply itself but thought I would
ask on here to see if any one has dealt with somethig like this before.

You could have a short in your motherboard or add-on cards. When an
output is shorted most power supplies will refuse to start. You can
test with another power supply or another PC to determine where is the
fault.

Hey Mike,

I agree.

I don't think its the power supply, why would it output all the
voltages correctly when not plugged in?

I think the short is maybe causing the current to be pulled over the
specs, so that causes the power supply to cut off (some sort of
protection circuit built into these things?).

I will unmount the mother board and unplug everything, plug it all
back up, and cross my fingers!

Thanks for the tip!

Cheers!

Nate

UPDATE

After screwing around inside the casing, i unmounted the motherboard
and then remounted it, not screwing anything but the HUGE cpu heat
sink back to the case...powers up though its still shorts against the
case some where...no idea but after enough fiddling i should be able
to isolate the short...

now to see how far i can get the unit to boot up (hopefully onto the
desktop!)

cheers!

nate

n8ball wrote:
Hello!

I have a problem with my Optiplex 745 power supply, model H275P-01.

I printed out the ATX 24 pin pinout and whats odd is when I short the
pins to turn the unit on, its turns on ok.

I read the voltages out and I get what is in spec when not plugged
in...

However, WHEN i plug in just the ATX aux 4 pin connector (for the chip
extra power) the power supply works fine, but when I plug in the main
24 pin connector it stops....

My questions:

Do you think the power supply needs recap or the motherboard is at
fault here?

I opened the power supply but didn't see any leaky caps...

I thought it would be more obvious which caps are bad but it looks
like i might just have to recap the whole supply!

What would cause the power supply to run fine when not plugged in, and
give the right volts out, but not work when plugged in?

I assume its some bad caps in the supply itself but thought I would
ask on here to see if any one has dealt with somethig like this before.
I don't know if it's safe to short the turnon pins with it plugged in.
You could pull the wires to run the experiment.
I had an E-Machines motherboard that had a disconnect somewhere
between the front panel switch and the turnon pins on the power supply.
Bad news was that it still wouldn't boot with the power supply forced on.

On Sat, 1 Jan 2011 06:53:23 -0800 (PST), n8ball
wrote:

I have a problem with my Optiplex 745 power supply, model H275P-01.

I printed out the ATX 24 pin pinout and whats odd is when I short the
pins to turn the unit on, its turns on ok.

Please note: (I do not know if this also applies to this
particular model) There are DELL PSUs around that use standard
plugs but with a slightly different wiring !

--
Kind regards,
Gerard Bok