PowerMac G5: No cold start

[pentium]

Weird.
So I power on my G5 tonight and....nothing.
I get fans but it acts dead. I leave it on for a bit and then cycle power and then it comes to life.
After multiple tests, it appears that my G5 will now only chime and start up if you first start it cold, let it run for a few minutes, then cycle the power. It reminds me of my old badcap-ridden AMD board where it would not POST until you power cycled it after a few seconds.
It has no badcaps, the LCU has been repaired and the only problematic spot on the board where coolant was eating at it has been cleaned up.
What could be causing this? I did get it briefly giving thre blinks "incompatible memory" but have not seen it since.

[Toasty]

Re: PowerMac G5: No cold start

>>It has no badcaps<<

PSU caps are good too? I'd monitor the voltages to verify that it's all up and where it should be. Has it the LiteOn Tesla Converter PSU? p/n: 614-0307 ?

[toastygoodness]

Re: PowerMac G5: No cold start

did you reset the PRAM and stuff like that?

[pentium]

Re: PowerMac G5: No cold start

PRAM was reset.
PSU in these towers are also of good quality. most die from drowning in a leaking LCU.

[severach]

Re: PowerMac G5: No cold start

ESR goes down as the temperature goes up. Sounds like caps to me. What's the status of the board?

You've recapped it before and by now maybe one of the replacement caps is starting to go bad. As fast as a G5 eats perfectly good Rubycon MCZ I wouldn't expect anything to last long cooking in that oven.

You've not recapped it because all the caps look good and are a good brand.

You've recapped the bad ones and no more look bad. I've partly recapped one G5 twice. By the second time it was clear as the cap death moved in an orderly fashion from one side to the other that caps in G5 are only a matter of time. When one goes they are all close. A partial recap will always result in endless rework. All or nothing for the G5.

[stj]

Re: PowerMac G5: No cold start

weak point of well designed psu's is the startup cap.
usually 2.2-47uf at around 35-50v

[pentium]

Re: PowerMac G5: No cold start

This isn't an imac G5, it's the PowerMac G5.



They don't have cap issues. The main thing they die from is a leaking LCU or detached memory controller (in which case, the system is REALLY brain dead).

[seanc]

Re: PowerMac G5: No cold start

I'm sure I've seen someone repairing a PowerMac G5 PSU around here somewhere...

Here's one: https://www.badcaps.net/forum/showth...ghlight=liteon
Possibly this: https://www.badcaps.net/forum/showth...ghlight=liteon

Keyword.. Liteon.

Hence Toasty's earlier question.

[Toasty]

Re: PowerMac G5: No cold start

Well, I've 3 dead PowerMac power supplies that say different. Plus one on the way in...

[AudioCraZ]

Re: PowerMac G5: No cold start

I have repaired many powermac with bad power supplies. I would always check that first.

[stj]

Re: PowerMac G5: No cold start

any psu can lose the startup cap, it's small and dont last well.

[toastygoodness]

Re: PowerMac G5: No cold start

yeah i agree with the startup cap if you've done all that good stuff.

[pentium]

Re: PowerMac G5: No cold start

>_>
<_<
>_<
Fine!
I'll take it into work tomorrow and throw it against a pile of PSUs we got and see what happens.

[Toasty]

Re: PowerMac G5: No cold start

Well, the one that was on the way arrived. Not at all like your problem though. Total death. Took out a switcher, fusible resistor, fuse, and some small transistors. And the Ltec & Taicon caps all check ok.

Again, which PSU is it? PLEASE

Can you at least monitor the PSU voltages when it does this and see? Maybe one is not coming all the way up, or is "bouncing". It is odd to have the fans run and not have the PSU come on.

There are also a few "sense" lines that feedback to the PSU from the mobo. A 5v and a 3.3v. The 12V lines (12V1, 12V2, 12V3) are all sourced from the same bus, they just go to different connectors. So 12V on P3 is the same 12V on P2.

5VSTBY is Pin 1 on P1.
25V is Pin 8 on P2
On/Off is Pin 14 on P1
TACHO is Pin 3 on P1 (fan speed monitor)

I'm sure you've checked, but there was some chat about a video card problem and or re-seating it.

Good Hunting!
Toast

[pentium]

Re: PowerMac G5: No cold start

I know the Quad G5 PSUs are a different design. I know a fair number of them like to blow up.
I forgot to pull mine out to check. It's a real bitch to remove. >_>

[seanc]

Re: PowerMac G5: No cold start

I know a guy who had a brand new Quad G5 in storage for backup purposes.
The day came where it was needed, plugged it in - BANG!

[stj]

Re: PowerMac G5: No cold start

caps probably leaked or depolarised in storage.

[Toasty]

Re: PowerMac G5: No cold start

*BUMP* Was this ever resolved Pentium?

[pentium]

Re: PowerMac G5: No cold start

I got assed into tearing my box apart because I dropped a screw which slipped under the PSU.
Wow, the PSU was actually the fault.

[seanc]

Re: PowerMac G5: No cold start

Pictures?