4,1 Mac Pro Won't Power On after Sudden Shutdown

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
Machine suddenly shutoff and now won't power on.

Followed steps in tech manual; red LEDs flash when power connected and STBY yellow LED lights when diagnostic button pushed. Nevertheless, I replaced the power supply and it did power up and boot normally and stayed on for about 8 hours before I did a manual normal shutdown. Restarted the next morning normally then another abrupt unattended shutdown while idle after about an hour. Now won't start at all.

I have taken it down to almost (everything except removing the CPU from its socket) a minimal configuration per the manual and still can't start it even from the jumper pads on the back plane. So it must be the backplane or the CPU tray, right? I am guessing the backplane board as I remember Apple replacing that during the 4th year of ownership.

Is it worth replacing the backplane in this thing or just getting a used 2010 for about $500? Will the 4,1 2 x 16gb 1066mhz dimms work in a 2010? It is a pity to trash this machine as the chassis alone is such a beautiful and well made thing.
 

MIKX

macrumors 68000
Dec 16, 2004
1,756
647
Aussie in Japan
I recently had the same problem .. . but after removing and thoroughly de-dusting the PSU I got CPU A working.

Did you check the Northbridge heatsink retainer spring rivets on the CPU tray? They break with surprising frequency.

replacing them and re-newing thermal paste has fixed quite a few cMPs.

In the end it seems it was a CPU socket problem. I ended up getting a refurbished CPU tray with 32gb ECC RAM.
works like a charm now.

Probably just old age.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
I recently had the same problem .. . but after removing and thoroughly de-dusting the PSU I got CPU A working.

Did you check the Northbridge heatsink retainer spring rivets on the CPU tray? They break with surprising frequency.

replacing them and re-newing thermal paste has fixed quite a few cMPs.

In the end it seems it was a CPU socket problem. I ended up getting a refurbished CPU tray with 32gb ECC RAM.
works like a charm now.

Probably just old age.
That I haven’t tried. Thanks for the suggestions. I will probably take it to a repair shop.
 

msh

macrumors 6502
Original poster
Jun 13, 2009
331
107
SoCal
It was the logic board (backplane). But I will keep in mind the heat sink rivets and new paste for the cpu.
 
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