MP 1,1-5,1 MP 3,1 not booting

[Carl C]

Hi! My MacPro 3,1 early 2008, OS 10.10.5, stopped abruptly working. On start up the power-on LED illuminates, the posterior fan, the power supply fan and the video card fan spin, the LEDs on the memory riser cards flash, then go off. No chime, no video. The diagnostic LEDs on the logic board are all off, pushing the DIAG_LED button LED #2 goes amber and LED #9 goes green, LEDs #7 and #8 stay off.
So far I:
reset the SMC (many times)
reset the Real Time Clock
- removed all unnecessary hardware (HDs other than system, optical drive, PCI cards other than video, RAM modules other than 4 x 2Gb (properly seated).
checked the system HD on another MacPro 3,1
reseated the system HD in all 4 bays
tried 2 different, working, video card
reseated the video card in all PCI connectors
changed the battery
tried a SYS_RST start up
checked the power supply cables #1 #2 and #3
checked the loudspeaker cable

all to no avail.

Has somebody any suggestion?
Thanks for your help!
Carl

 

[bax2023]

I would check if the rivets holding the chipset heatsink are fine. Intel 5400 chipset in MP3,1 can get REALLY hot.

Other than that, I'm sorry to say but I think that logic board failed.