Dell GX280 PSU dead - Or is it?

[fuxxy]

Just recieved this GX280 desktop.

Plug in, orange status light on the motherboard. A tap of the power switch results in a momentary "something" happening. Holding down the power button results in action out of the system, but no boot. Swapped PSU with known good replacement and the PC powers on and works normally.

The next day, I plugged the "Bad" PSU into my tester, and not only did the PSU come on, but it presented all pretty normal voltages! Pic of tester included.

If I let off of the "Test" button momentarily and pressed again, I got an error of no PS_OK. If I left it off for a few (about 5) seconds, it would come back good again.

The only known physical problem I can identify is a faulty fan. The question is, what should I do at this point? I'm tempted to hit it with a heat gun and see if anything goes out of spec.

[stj]

Re: Dell GX280 PSU dead - Or is it?

that's an early version of a pile of crap i'v been fixing for someone.

that ceramic cap infront of the main fet needs to be upgraded to 2Kv or even 3Kv or it will run hot & eventually take out the fet + driver.

[fuxxy]

Re: Dell GX280 PSU dead - Or is it?

Can you elaborate a bit on which one is the "main FET"? Also, is 11.2 close enough to -12V? I see only one adjustment POT on this thing and it only changes +5V and +12V

[Pentium4]

Re: Dell GX280 PSU dead - Or is it?

The main Fet is the silicon attached by itself to that smaller heatsink, so that little ceramic directly below it

[stj]

Re: Dell GX280 PSU dead - Or is it?

yea, the light-brown( and gets darker as it overheats) thing infront of the big black part on the small heatsink.

on the newer active PFC version of this supply.
[H240AS-00]
the cap overheats.
then the fet fails and destroys:

the fet,
the fuseable resistor on it's right,
sometimes the main fuse.
a fast diode to it's left
2-3 smd parts under the board,
and a shitload of stuff on a controller pcb hidden on it's side behind the heatsink.

these dell shit are a bastard!!!!!
http://en.community.dell.com/support.../19423875.aspx

[Pentium4]

Re: Dell GX280 PSU dead - Or is it?

It looks well built. Hipro? It just looks like the primary heat sink is way too small for that sort of form factor, and that already small heat sink doesn't even fins to help the air flow. I think that contributes to the ceramic overheating. Upgrading the heat sink might be difficult, but maybe adding a FET with lower RDSon would help the heat problem

[stj]

Re: Dell GX280 PSU dead - Or is it?

it's a very good fet already.
st w12nk90z

[fuxxy]

Re: Dell GX280 PSU dead - Or is it?

As I said earlier, I have two of these, identical. One doesn't work at all, the other works fine, but fan doesnt spin. I'm thinking these rely heavily on active cooling and when that fails, boom!

[Agent24]

Re: Dell GX280 PSU dead - Or is it?

I had Power_Good signal problems on a SFF GX280 PSU due to a bad PWM controller supply\startup capacitor.

[stj]

Re: Dell GX280 PSU dead - Or is it?

As I said earlier, I have two of these, identical. One doesn't work at all, the other works fine, but fan doesnt spin. I'm thinking these rely heavily on active cooling and when that fails, boom!

did you test the fan?
if you did, just connect it directly to the supply lines.

thermal fan control is a joke in these compact systems - you really need it full-on all the time.

[fuxxy]

Re: Dell GX280 PSU dead - Or is it?

The fans on my model are 12V, not sure what the supply voltage is. Both fans' bearings were shot and neither spun at full speed - one didnt spin at all.

[stj]

Re: Dell GX280 PSU dead - Or is it?

did you test them on a seperate supply?
there is a speed control circuit on the psu.

unsolder the fan red-wire & connect it to where the main yellow wires come from.

[fuxxy]

Re: Dell GX280 PSU dead - Or is it?

Thanks for that! The fan control circuit was only putting out 4.15V. The fans on both of these PSU's need to be replaced anyway, I'll connect them to 12V when they get here!

[fuxxy]

Re: Dell GX280 PSU dead - Or is it?

Turns out, the problem with one is bulging caps on the motherboard. Fixed those and it worked fine!. I replaced the fan in the PSU and connected it to +12V.

The second PSU I'm working on now. I get no response from my PSU tester, next step is testing for 5V standby