Early 2009 - Distinguishing faulty PSU / backplane

VLSI

macrumors newbie
Original poster
Nov 2, 2015
3
0
London UK
Hello, I'm new here! I have a friend's dead 8-core early 2009 MacPro in front of me with a question mark hanging over its backplane, PSU or processor board and wonder if someone could give me some pointers please as I haven't found the answer by searching.

History: Has been working fine, had a replacement PSU a year or two ago, the old one was obviously intermittent and changing it solved the problem

New symptoms: a couple of random shutdowns while unattended, now appears power dead from the outside.

Tests so far:
5V STBY LED always lights when pressing DIAG button.
O/T CPUA and CPUB flash briefly when applying AC power.
Stripped down to minimum config - no change.
Installed processor cage and board without processors - no change.
Jumpering SYS_PWR does not cause the fans to start up or bring on CPU warning LED on CPU board.

This is where the technician's guide loses the thread a little, because although it tells what to expect in a good machine, there's no route to follow if you can't power up at this stage. Logically, I would suspect the PSU, backplane, or CPU board, but is it possible to localise further without substitute units? I am an experienced electronic tech with instruments at the ready...

TIA
VLSI
 

VLSI

macrumors newbie
Original poster
Nov 2, 2015
3
0
London UK
Ah yes that's the same thing. Thanks for the link tho.
Update: it's fixed, although we don't know which part was borken because they were all swapped at once. In effect it's a new machine with the old HDDs, CPUs, RAM, GPU and PCIe cards transferred. Time didn't permit any more investigation!
Cheers
VLSI
 

delnerdo

macrumors member
Nov 16, 2011
57
11
I am walking through the minimum configuration process and get a startup chime with processor and heatsink removed but no chime when I reinstall them (with new thermal compound).
I don't think the temp sensor is bad because the cpu cage fans run at low speed. Could this implicate the cpu?

All diagnostic leds are indicating performance as expected.

Aside from replacement, is there any definitive way to diagnose a faulty psu?

2009 4,1 2.9GHz 4 cores
 
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delnerdo

macrumors member
Nov 16, 2011
57
11
<rant> it's tragic how modular and well designed is the interior of the original mac pro, while the essential information for basic diagnostics is kept out of our reach thanks to dmca and overzealous moderators who don't understand the meaning of fair use wrt copyright act </rant>

rest assured that i went out and bought a new computer, so sharing technical know-how will not halt the wheels of industry.
 
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