dell optiplex power supply

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.

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.

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

SFF style box and motherboard? The H275P-01 is the part number for the SFF box.

I've seen bad capacitors on the motherboard in those. I don't recall any problems with the power supplies.

The larger Optiplex 745 and 755 motherboards seem to last without problems. No power supply problems that I've seen on either the 745 or 755. (The GX620 series is another story).

Please invest in a cheapo ATX power supply tester. Some have loads inside which are needed to properly test the power supply.

Inconclusive. The biggest power load is the CPU. When you apply a load to the power supply, it could be shutting down because the power supply has a problem. Similarly, if the load is shorted, the power supply could be protecting itself. I can't tell from here.

Many of the caps I have replaced show no indicatation of bulging or leaking. Sometimes, it's nothing more than a slight tilt caused by a slight bulge in the rubber plug on the bottom of the capacitor.

What does show a problem is an ESR capacitor meter.

Many more types available.

See my previous comment on the inability to distinguish between a defective power supply, that craps out under load, from a shorted motherboard.

Nope or at least maybe. If the caps in the power supply were bad, then my *GUESS* is that it also will not run without a load. Hard to tell from here.

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 !