Delta/HP PSU 3.3v short

[pentium]

I'm literally about to run out of the shop for th night but I have an HP system with problems. You plug it in and the front panel controller for the system comes up and behaves normally but both pressing the power button or telling the controller to power up does nothing.
Pulled out the PSU (HP part 0950-3418) and shorting ON/OFF to ground doesn't seem to bring up the PSU like a normal ATX supply would but I noticed that while the 5 and 12v rails are good the 3.3v rail seems to have a 18 ohm short to ground which I suspect might be crowbarring the PSU. visually I saw nothing wrong and all caps appeared good but does anyone here have a clue what might be suspect? I'll start poking around tomorrow.

[PeteS in CA]

Re: Delta/HP PSU 3.3v short

Are you sure that 18 ohms isn't a pre-load resistor? It would not be enough to trip current or power limit, as the current would be a little over 1/10A, and the power about 3.5W.

[pentium]

Re: Delta/HP PSU 3.3v short

Ah, yes, there appears to be a 18 ohm resistor hidden away under a coil.

Okay, well then that rules a short there out. :/
Well after blowing the PSU out I find no blown caps (it's all Rubycon and Nichicon), no burned components, no damaged components and nothing improperly attached. It looks really good. The ON/OFF line by the way has 4.1v on it as well when plugged in and under all conditions.

[pentium]

Re: Delta/HP PSU 3.3v short

Anyone? I cannot source a repalcement PSU.

[LDSisHere]

Re: Delta/HP PSU 3.3v short

Can you post some good pictures of the supply? Also what are the exact voltages it is putting out on 5vsb, 12V, 5V and 3.3V lines?

[pentium]

Re: Delta/HP PSU 3.3v short

Here's your pics.




As said, the PSU is doing something. The system controller comes up however the instant the system is expected to turn on it dies and resets as if it switches over to another voltage rail which has not come up.



+5sb is 5.11v
+12, +5 and +3.3v are dead, which make sense because the PSU isn't on.

[LDSisHere]

Re: Delta/HP PSU 3.3v short

I noticed in your first post that grounding PS_ON would not start the supply. Would it twitch the fans at all?

If yes, then I would check the voltage on each rail while grounding the PS_ON wire. If you have a Fluke meter with a Min/Max function this would be a good time to use Max.

The next step would be to identify the supervisor IC. This should be the chip that is giving you the PS_ON voltage, this chip should also be connected to the Power Good wire which is normally grey.

The idea is to see if the supervisor chip is sending a signal to the primary side to start up. Determining this should allow you to tell if you problem lies on the primary side or secondary side and where you should focus your attention.

Out of curiosity how old is this computer? The date code on the supply reads 9851. Could that possibly be the 51st week of 1998?

[pentium]

Re: Delta/HP PSU 3.3v short

It's a dual PIII Xeon system so it is in that timeframe.
To make the fans twitch, first you must short ON/OFF to ground, then you have to short the FANS lead. It has to be done in that order or else nothing happens.