MP 1,1-5,1 Mac Pro 4.1 no image - cooked?

[Xebrafish]

I have a classic 2009 Mac Pro from a friend that doesn't display or do anything after powering on and chiming. Unsure what troubleshooting steps to do from here...

Relevant specs:
Dual Xeon E5520 2.26GHz 4C, Sapphire Pulse RX580 8GB, 6x 2GB 1066MHz ecc RAM correctly installed, vanilla MacOS Mojave (no patchers or OCLP) installed on a Samsung EVO SATA SSD on an OWC PCIe SATA3 card, PCIe USB3 card, upgraded wifi/Bt card BCM9436CD, 4x 4TB HDDs in RAID10

Startup sequence:

1. Hit power button
2. Red LED next to ram slot 4 blinks once, very short
3. Optical drive initializing sounds
4. Harddisks spinning up
5. GPU lights up and fans spin
6. Chime
7. Display is on, backlight on, but no image (known working display)

! The machine immediately shuts down when the power button is pressed again; compared to long hold to power off during regular use.​

Troubleshooting steps taken:

• Removed all PCIe cards, optical drive and HDD's except GPU
• Swapped RAM around
• Removed a couple of RAM sticks
• Cleaned out the machine
• Visually inspected mother- and CPU board; the Northbridge heatsink is firmly attached and clean
• Reset the SMC
• Reset PRAM/NVRAM (which works, caps lock lights up during reset)
• Connected the display through both direct DVI and with a DP adapter

Noteable constatations:

• No diagnostic lights on
• Display backlight is on when connected, indicating a signal from the GPU
• A feint rattle or buzz noise (more an electronic buzz) coming from the rear of the case. Either from the PSU or the GPU area. I don't think it's a fan noise. Could be nothing? Could be a bad cap? Could be a fan getting old?
• The machine chimes every time I've started it, when all components are installed or when most of them are unplugged
• The OWC PCIe card has green and yellow LED's, indicating SATA slot population and R/W activity respectively, these lights do not turn on during machine startup, as they should. This indicates the machine doesn't talk with this card at any time (before and or after chime)

I have a similar machine myself, but I'm very reluctant to try and swap components. I don't want to possibly ruin my own stable running cMP...

Any troubleshooting steps I can take? Advice?

Thanks a lot

 

[Bigwaff]

Have you checked or replaced the BR2032 PRAM battery?

 

[Xebrafish]

That's a good call! I checked before and the cell had 2.9V. I just now replaced it with a fresh CR2032 just for testing purposes and I reset the PRAM but nothing changed.

 

[MrScratchHook]

That's a good call! I checked before and the cell had 2.9V. I just now replaced it with a fresh CR2032 just for testing purposes and I reset the PRAM but nothing changed.

have you tried putting the gpu in slot 2? also i highly suggest borrowing another gpu to test.

 

[Borowski]

If it is still a 4.1 (not crossflashed to 5.1) Mojave won't boot and stops with the prohibition sign, not visible due to no bootscreen. Latest OSX for 4.1 was El Capitan.

For better analysis put in a compatible Apple GPU and install supportet OS.