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MP 1,1-5,1 Strange shutdown behaviour

RickyHunter

macrumors member
Original poster
Nov 9, 2017
66
6
Spain
Hi there.
Let's see if I'm able to explain what is happening.
I've got a CMP4.1 upgraded with 5.1 firmware. No other hardware upgrade done. Almost 3 years have passed since I upgraded the firmware, so the issue is not related to that.
All of the sudden, the computer stops working. Sometimes I see a red light flashing several times, sometimes not. Sometimes if I disconnect the power supply (I've got a remote control for the socket) and then I reconnect it, the computer starts again without pushing the power button. Most of the times it's not going to start again.
What I've done until now: with the technician guide I've "dismembered" everything several times. Without doing anything but assembling it again, sometimes it works, sometimes not.
The power supply seems to work properly, so as the main motherboard and the cpu motherboard.
Last time (yesterday), I disconnected every cable, I got rid of everything but: fan+cpu tray chassis, bluetooth and wireless modules. No powerup. I inserted the cpus tray: no powerup... I inserted it again: powerup. Then I connected everything again and I was able to work a little bit, then the damned sudden shutdown happened again. Once I was able to boot again (switching off and on the power supply with the remote), but after that, it shutdown again and no powerup.
I tested the power switch and it's working.
The computer usually works again if I detach everything, let it rest a couple of days and then reconnect the cpus tray.
Any ideas of what can I do to find out the issue? I followed each step from the technician manual, and it should be a working computer. The only thing I didn't try is to unmount the cpus (I still don't have the right tools to do that).
Thank you.
 

tsialex

macrumors G3
Jun 13, 2016
8,377
8,914
Hi there.
Let's see if I'm able to explain what is happening.
I've got a CMP4.1 upgraded with 5.1 firmware. No other hardware upgrade done. Almost 3 years have passed since I upgraded the firmware, so the issue is not related to that.
All of the sudden, the computer stops working. Sometimes I see a red light flashing several times, sometimes not. Sometimes if I disconnect the power supply (I've got a remote control for the socket) and then I reconnect it, the computer starts again without pushing the power button. Most of the times it's not going to start again.
What I've done until now: with the technician guide I've "dismembered" everything several times. Without doing anything but assembling it again, sometimes it works, sometimes not.
The power supply seems to work properly, so as the main motherboard and the cpu motherboard.
Last time (yesterday), I disconnected every cable, I got rid of everything but: fan+cpu tray chassis, bluetooth and wireless modules. No powerup. I inserted the cpus tray: no powerup... I inserted it again: powerup. Then I connected everything again and I was able to work a little bit, then the damned sudden shutdown happened again. Once I was able to boot again (switching off and on the power supply with the remote), but after that, it shutdown again and no powerup.
I tested the power switch and it's working.
The computer usually works again if I detach everything, let it rest a couple of days and then reconnect the cpus tray.
Any ideas of what can I do to find out the issue? I followed each step from the technician manual, and it should be a working computer. The only thing I didn't try is to unmount the cpus (I still don't have the right tools to do that).
Thank you.
Open your PSU and inspect if any capacitors are bulged, some ACBel PSUs have capacitors prone to bulging and it's a common thing after 10+ years.

Btw, when replacing your PSU try to buy a Delta PSU from a mid-2012.
 

RickyHunter

macrumors member
Original poster
Nov 9, 2017
66
6
Spain
Open your PSU and inspect if any capacitors are bulged, some ACBel PSUs have capacitors prone to bulging and it's a common thing after 10+ years.

Btw, when replacing your PSU try to buy a Delta PSU from a mid-2012.
Already did that. No capacitors bulged, no strange things happened in the psu. I forgot to mention I opened it and I cleared it with compressed air.
Do you think it's only the psu that needs to be replaced?
And why sometimes it boots and sometimes doesn't?
 

tsialex

macrumors G3
Jun 13, 2016
8,377
8,914
Already did that. No capacitors bulged, no strange things happened in the psu. I forgot to mention I opened it and I cleared it with compressed air.
Do you think it's only the psu that needs to be replaced?
And why sometimes it boots and sometimes doesn't?
No, can be elsewhere, PSU is the usual suspect.

It's very difficult and time consuming to identify the real problem without having dataloggers and scopes connected, it's cheaper to buy another used Mac Pro to test the parts of the problematic one.

To diagnose this type of problem involves two Mac Pros and organized test of each part, one by one.

There is no magic bullet, just usual suspects, but buying PSU, backplane and CPU tray is costlier than a full Mac Pro.
 
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RickyHunter

macrumors member
Original poster
Nov 9, 2017
66
6
Spain
No, can be elsewhere, PSU is the usual suspect.

It's very difficult and time consuming to identify the real problem without having dataloggers and scopes connected, it's cheaper to buy another used Mac Pro to test the parts of the problematic one.

To diagnose this type of problem involves two Mac Pros and organized test of each part, one by one.

There is no magic bullet, just usual suspects, but buying PSU, backplane and CPU tray is costlier than a full Mac Pro.
Yeah, it's what I was thinking to do, but before I wanted to post something here where I know there are so many experts like you that can suggest me cool ideas.
Thanks mate!
 
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