LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

[yomamaphat]

Hi all,

This is from a PowerMac G5 Quad 2.5GHz. I wasn't there when it died, so I don't know of any smells or sounds that might have occured. Inside it looks clean though, can't see any vent marks, signs of heat, or anything.

The big black caps are "Ltec", some of the smaller brown ones are "taicon" and "Ltec" and some don't seem to say their brand as explicitly.

I power it on by shorting green, like I have with ATX powersupplies, although this has bizarre connectors it still works.

A relay clicks, the fans twitch then stop. A few seconds later a steady buzz starts and continues until I unshort the green. The buzz is coming from right near the relay (maybe the black thing behind it? "L1"? silkscreened on the PCB).

I measured what happens to the voltage on the 5 and 12 V wires. The 5V spikes up to 1 - 3 volts and then falls quickly to zero. The 12V barely goes up at all, just showing < .05V

I haven't looked at the underside yet, but will soon. Any ideas? What to test next?

Thanks in advance!

[yomamaphat]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

It's not L1 that would be buzzing, maybe BD1 (can rectifier bridges buzz?).

[stj]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

only coils can buz.

[yomamaphat]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

Well I have thoroughly looked at both sides for physical damage and can't find anything. Can I test the switching transistors without removing them like this guy says?: http://www.mikesarcade.com/cgi-bin/s...e=psrepair.txt

I know I have not given much info to trouble shoot with, but any suggestions on what I should first start testing would be appreciated. Is the above guide a good place to start?

Thanks!

[stj]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

the fan twitch makes me suspect there is a short-circuit shutting the supply down.

can you start the psu when it's not connected to the motherboard?

[yomamaphat]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

No, seems like the same results connected or disconnected.

[stj]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

disconnect it and meter the resistance between ground and each voltage line on the plug.

see if one looks a lot lower than the others.

[yomamaphat]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

I got 1.65k on the 5V, 940 on the 3.3V. On 12A & B I get 3.1k. (all these use the chassis ground)

On the 12mpu1 & mpu2 I get just 2 ohms to its grounding line. (This has it's own isolated ground apparently. To the chassis I get 22.1k from the either positive and negative.)

Should I try to trace which components are in line with the 12V mpu rail and maybe do some pulling and testing?

[stj]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

yes, start with the main diode(s) from the transformer to the 12vmpu lines.
if the diode isnt shorted then check the caps.

[yomamaphat]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

I found damage, hopefully not caused by me. It's in a spot where I don't think I did it. I'm not sure why I missed it when looking the unit over initially though...

I believe the main diode is OK.
I have no ESR meter for testing caps, but my dad in another state might and I'll be moving there in a couple weeks. I'll probably put this on the back burner until I make my move.

Thanks for the help so far.

[stj]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

you dont need an esr meter to find a short,
remove the suspect part and meter from the connector to see if the 2ohm reading goes up.

[yomamaphat]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

Cool, that's a good idea. I'll do that when I get moved. Probably 2 - 4 weeks. Thanks again.

[Toasty]

Re: LiteOn 1000W Model: PA-5102-1-LF Part no. 614-0336

Bloody hell. Put the name of the system and PSU in the thread ~somewhere~. The TITLE is a good start.

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