MP 1,1-5,1 Mac Pro 2,1 Powers On but No POST, No Chime, No USB — EFI_GD LED Lit

[Hil_]

I’m troubleshooting a Mac Pro 2,1 (Late 2007, 8-core) where the CPU sockets are soldered directly to the main logic board — so there is no separate CPU tray like in the standard tower model.

The system powers on via the front panel button and can be forced off with a long press. However, it shows:

• No chime
• No video output
• No USB response (Caps Lock unresponsive) (though powering the mice red light)
• No HDD activity

Already replaced:

• Power supply (PSU)
• Logic board (backplane with CPU sockets)
• CPUs (both replaced in the sockets)
• Both memory risers and all RAM
• GPU (using known-good Mac-compatible NVIDIA card)
• CMOS battery
• Front panel with power button (edited)

Observations:

• EFI_GD LED lights green after powering on
• TRICKLE LED lights only while holding DIAG or RTC reset buttons
• CPU A/B Overtemp LEDs flash briefly (normal POST signal)
• GPU spins at max fan speed
• USB ports have power, but Caps Lock never lights
• RAM riser LEDs flash once when powering on
• No 5V standby LED remains lit at rest
• No signs of POST continuing beyond EFI

Tested with: Minimal config: only 2 FB-DIMMs in correct paired slots on Riser A, no GPU, no drives — still no chime

Question:

Since EFI firmware loads (EFI_GD LED confirms), but the system halts before USB init, what could still be preventing full POST?

Could this be:

• Bad logic board even after replacement?
• Deep CPU socket issue despite both CPUs and logic board being replaced?
• PSU voltage sag under load? (unlikely...)
• Corrupted firmware/SMC/NVRAM state?

Worth mentioning: prior to this issue, the machine experienced sudden shutdowns (as if the power was cut off). Later, it entered complete silence. I cleaned and replaced all the components listed above, but with no results.

Thanks in advance for any kind of advice!

 

[reader50]

With every major component changed, it's hard to fault any of them. There's not many common elements left.

Are you using the same keyboard / mouse for testing, and were they plugged in during minimal-config testing?

Any secondary boards that weren't changed, like an airport/bluetooth board? (I've never worked on a 2,1)

Is the power cord the same one all along? How about the outlet it's plugged into (or UPS).

 

[Hil_]

thanks for response. Small correction: the power on switch wasn't replaced.

Same keyboard and mouse (Apple) tried front and back panel ports. Caps lock is unresponsive, but mouse sensor (red light) is on.

Airport and Bluetooth cards were removed.

PSU is identical, though i also tried it with the original. Power cord is the same all along.

At the beginning, I assumed the logic board had failed, soi replaced it with no response, after that, the memory modules, then the memory risers, then the CPU (x2) units, and at each step there was no change.

My next step is to detach one of the CPU for each attempt. (I also tried booting without a graphic card and with an ATI card)

I wonder what else I can try...

 

[reader50]

Try a different keyboard and mouse, tested good on another computer. A bad USB device might lock up the boot process - though I'd expect it to muck things up after POST. And try a different power cord for good measure. Desktop Macs typically use office-style power cords. You can borrow one from a printer, copier, etc.

If those don't do it, you're into testing each component in a working Mac Pro.

 

[Hil_]

Thanks, I will give it a try.