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Den_John

macrumors newbie
Original poster
Jul 22, 2016
9
3
Hi,

I have an issue: several years ago I received a Mac Pro 4.1. Quad-Core 2,6Ghz, 3x1GB RAM, 640GB HDD and a GT120 gpu. I've flashed the Mac Pro towards a 5.1 model and installed an Intel W3680, 3x8GB DDR3 ECC RAM, a EFI flashed Radeon HD7950 and a Samsung SM951 512GB m.2 SSD on a HyperX PCI-E adapter.

I've used this setup for more then a year until last week the unit started to freeze. Some random freezes, I've experienced it for 3 times last week. Coolers kept spinning, no hard drive activity and the screen stayed blank. After a hard reset, the Mac Pro worked again until a couple of days ago, now the unit can't boot anymore. I can't even hear a chime, nor see disk activity... I think the unit is dead.

I've googled (and found the service manual) and tried several "cures" in the hope to revive my MP. Tried the minimal startup without memory, placed the original cpu, gpu, memory... back in. Nothing seems to help. I even replaced the BR3032 battery and checked the northbridge heatsink (that one is still attached fine).

When I plug in the power cable, the 2 red led's on the motherboard and the one on the cpu-tray are visible turning on and off (normal behavior). When the unit is off but the power cable is attached, the diagnostic led for 5V is solid amber. When powering on the unit and checking the leds: PSU (solid green), 5V (solid amber), SYS PG (solid green), EFI DONE (solid green) but GPU OK keeps blinking green. The front led is solid white. It's not blinking. (even without memory, the front led stays solid white)

I don't understand why the system is not booting, is not giving a chime and the diagnostic led is blinking on GPU OK even there's no gpu connected in the system.

fyi, cpu (the w3680) and northbridge temperature was always around 40 degrees celsius, memory (3x8GB) around 40/45 and the disks around 35.

Any thoughts?
 

William_si

macrumors regular
Apr 4, 2016
188
55
Croatia
Do you have the ability to measure power (voltage) on a 12V lane or the power draw on the wall (guess work then, but better than nothing)?

I've seen similar with too much draw on 6 pin but the GT120 can't cause that, so the possibility would be that the sole 12V lane in your PSU is dead/near dead, if too far below spec most components do... weird things.

Do you have a spare CPU tray you can pop in? And tried the GT120 in Slot 3/4 (they are wired differently at x4)?
 

h9826790

macrumors P6
Apr 3, 2014
15,659
7,864
Hong Kong
The main suspects are

1) PSU
2) GPU
3) logic board
4) CPU tray

GPU is the easiest one to diagnosis. Just remove it and the Mac Pro should able to boot. If not, then it's not the GPU's fault.

The rest three are much harder to diagnosis, unless you have the spare parts. If you have any friends that have cMP, the easiest test is to take the CPU tray to there, and try to boot their Mac with your CPU tray. If it's not the CPU tray's fault, then you know it's not the CPU, not the tray, not the NB, not the RAM.

Also, if your friend has cMP, and if they don't mind. Swap the PSU should be the last test to do. After this test, you should able to know if it's the PSU's problem or the logic board's fault.

Anyway, 40C NB temperature sounds very unreal, unless you spin up the fans a lot, or your ambient temperature is freezing cold. However, that 35C disk temp suggest that your ambient is not very cold.
 

Den_John

macrumors newbie
Original poster
Jul 22, 2016
9
3
Do you have the ability to measure power (voltage) on a 12V lane or the power draw on the wall (guess work then, but better than nothing)?

I've seen similar with too much draw on 6 pin but the GT120 can't cause that, so the possibility would be that the sole 12V lane in your PSU is dead/near dead, if too far below spec most components do... weird things.

Do you have a spare CPU tray you can pop in? And tried the GT120 in Slot 3/4 (they are wired differently at x4)?

I measured 12,3V on both ends of the power supply. The readings where steady.
I don't have a spare tray to pop in :(
Tried to put the GT120 in slot 3 and 4, without result.

The main suspects are

1) PSU
2) GPU
3) logic board
4) CPU tray

GPU is the easiest one to diagnosis. Just remove it and the Mac Pro should able to boot. If not, then it's not the GPU's fault.

The rest three are much harder to diagnosis, unless you have the spare parts. If you have any friends that have cMP, the easiest test is to take the CPU tray to there, and try to boot their Mac with your CPU tray. If it's not the CPU tray's fault, then you know it's not the CPU, not the tray, not the NB, not the RAM.

Also, if your friend has cMP, and if they don't mind. Swap the PSU should be the last test to do. After this test, you should able to know if it's the PSU's problem or the logic board's fault.

Anyway, 40C NB temperature sounds very unreal, unless you spin up the fans a lot, or your ambient temperature is freezing cold. However, that 35C disk temp suggest that your ambient is not very cold.

Then the NB temperature reading wasn't correct but I'm sure the heatsink is still pretty attached to it.

Unfortunately, I don't know anyone with a cMP :(
 

h9826790

macrumors P6
Apr 3, 2014
15,659
7,864
Hong Kong
I measured 12,3V on both ends of the power supply. The readings where steady.
I don't have a spare tray to pop in :(
Tried to put the GT120 in slot 3 and 4, without result.



Then the NB temperature reading wasn't correct but I'm sure the heatsink is still pretty attached to it.

Unfortunately, I don't know anyone with a cMP :(

From your discription, it's almost narrow don't to logic board or CPU tray.

TBH, the cheapest way to fix it may be buy another cheap working 4,1. Then do the test on your own. And then sell the parts that you don't need (or keep them as backup).

A new tray cost you about $300, it's almost the same price as a used 4,1.
 
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