4,1 Power Issue

[rawweb]

Trying to help a friend fix his 2009 cMP. The unit will not power on. So far, I've tried everything I can think of from resetting SMC, different power plugs and power sources, RTC reset, reducing the computer to a minimum configuration (removed hard drives, optical drive, processor tray and board, PCIe cards, Airport, Bluetooth, Battery, PCIe fan, Processor Cage and the front panel board. No dice, no nothing.

I can verify via instructions in the apple service manual that the OVTMP CPUA and OVTMP CPUB LEDs flash when I plug in the power cord, and the 5V STBY LED illuminates, confirming power to the backplane board. I've attempted to jump the SYS_PWR solder pans, but the computer doesn't power on.

Any thoughts on this? My gut said power supply, but the manual seems to suggest that if the led illuminates, it's fine. Logic board?

 

[h9826790]

Sounds like the PSU is dead. Of course logic board is also possible. However, it's hard to know the answer if no 2nd PSU for testing.

 

[carpsafari]

You might want to check if the NorthBridge module is still attached, a snapped rivet would cause that too.

 

[h9826790]

You might want to check if the NorthBridge module is still attached, a snapped rivet would cause that too.

In this case, I think the Mac will still power on, but won't POST. Just white screen and no Apple Logo. However, I am not 100% sure about this.

 

[rawweb]

In this case, I think the Mac will still power on, but won't POST. Just white screen and no Apple Logo. However, I am not 100% sure about this.

Prior to its current state, the user was attempting a clean install of 10.11. The computer suddenly went into full fan RPM spin and no video. It was shut off holding the power button and has never powered back on since. Any clues there?

 

[rawweb]

Is there a way to test the power supply once it's pulled? Any ideas?

 

[rawweb]

Since 5V Standby illuminates following the service manuals instructions for minimal system configuration, should I just assume the backplane board is bad and order a new one?

Update: I ordered a replacement board. The next challenge will be flashing the new board 5,1 since this is an upgraded processor. Not sure if my friend kept the original or not.

 

[rawweb]

OK, if anyone cares, a new backplane board did the trick. Sort of...

I ordered a spare power supply and new board just to make sure. I knew going in that the PS was fine since it was throwing the standby voltage. Slammed the new backplane board in and it did the same thing. No dice.

In frustration, I pulled it out and put it back in, and viola. Works like a charm. No logic or explanation. I have no idea how it produced different results, because I quadruple checked every connection multiple times. Any who...