Power Mac G5 No POST

MultiFinder17

macrumors 68020
Original poster
Jan 8, 2008
2,010
707
Tampa, Florida
Hello all! I recently came into possession of a dual 2.5GHz Power Mac G5 liquid cooled system for the low, low price of free! On the plus side, the case is absolutely beautiful shape. On the downside, it doesn't POST. My first thought was naturally the LCS, but when I looked at it, it is perfect. No leaks. I'm rather stumped at this point.

When you turn it on, the front light comes on for a brief moment, then doesn't come on again. The computer stays on, with the fans running at a normal speed. After a minute or two, the fans gradually ramp up with no signs of a POST. It just keeps sitting there running the fans. Any ideas?

I'd be interested in getting it up and running again! I have a loaded 2.0DP on my desk that I love, but this 2.5 is in such beautiful shape. Thanks in advance for all your help!

Pic of my desk attached for your viewing pleasure - 2.0DP is on the far left :)
 

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bunnspecial

macrumors 604
May 3, 2014
6,716
3,262
Kentucky
I've been pouring over the Quad service manual a lot lately, but I think that some of this type stuff is the same on earlier G5s.

In any case, at least on a Quad a single flash of the power LED means no RAM or bad RAM.

Try pulling RAM in pairs, and be absolutely sure it's paired correctly.
 

eyoungren

macrumors Core
Aug 31, 2011
21,164
12,996
ten-zero-eleven-zero-zero by zero-two
Simple things first.

Try…pulling/reseating video card, pulling/reseating ram in pairs. Your situation is not unusual for a G5. But it could be video, ram or logicboard/cpu. Best to eliminate the first two first before focusing on the logicboard/cpu.
 

MultiFinder17

macrumors 68020
Original poster
Jan 8, 2008
2,010
707
Tampa, Florida
Thanks for the quick replies! I have ensured that known good RAM is installed in the properly paired slots, and the video card is good. I guess I should've been more clear about the light - it only comes on when the button is actively being pressed. As soon as you let go of the button to turn it on, it goes off. It'll come on if you press the button again, then go out as soon as you let go.
 

MultiFinder17

macrumors 68020
Original poster
Jan 8, 2008
2,010
707
Tampa, Florida
Then it's either the logicboard or one of the cpus.
Damn, that's what I was afraid of. Ah well; I originally nabbed this one because the case was in such beautiful shape anyway. Now to see how awful it would be to swap in the guts of my 2.0DP! Or I could use it for a casemod :D
 

bunnspecial

macrumors 604
May 3, 2014
6,716
3,262
Kentucky
Make sure all the CPU/LCS screws are snug. Again, if it's like the Quad(which I think it is at least in this respect) the two rearmost screws on the CPU cards provide power, and I think a couple of others on the LCS also serve as ground.

If nothing else, try pulling and reseating the complete processor assembly.
 

eyoungren

macrumors Core
Aug 31, 2011
21,164
12,996
ten-zero-eleven-zero-zero by zero-two
Damn, that's what I was afraid of. Ah well; I originally nabbed this one because the case was in such beautiful shape anyway. Now to see how awful it would be to swap in the guts of my 2.0DP! Or I could use it for a casemod :D
Well, it may only be one cpu that's bad. Or just the logicboard. You won't know until you get it apart.

Odds are seriously against both cpus AND the logicboard being bad.