MP 1,1-5,1 Mac Pro 4.1/5.1 Power Supply Issue?

[HKSig]

I have a friend's Mac Pro visiting due to problems. The description was "it won't turn on, then sometimes turns on by itself."

It did something similar here; after various troubleshooting (aka the service manual, pulling out/disconnecting everything), I did get it to come on. I found that if I unplugged it for ~48 hours, then plugged it back in, it would turn on normally. If I shut it down normally, it wouldn't turn on. Unplug for ~48 hours, turn it on, it was fine. I turned it off by holding down the power button; this time it came right up. Shut it down normally again, it wouldn't turn on.

Power supply or something else? I do hear a slight buzz that may be coming from the power supply. I have seen @tsialex post about many Mac Pro issues being due to the power supply; I'm leaning that way.

 

[tsialex]

I have a friend's Mac Pro visiting due to problems. The description was "it won't turn on, then sometimes turns on by itself."

It did something similar here; after various troubleshooting (aka the service manual, pulling out/disconnecting everything), I did get it to come on. I found that if I unplugged it for ~48 hours, then plugged it back in, it would turn on normally. If I shut it down normally, it wouldn't turn on. Unplug for ~48 hours, turn it on, it was fine. I turned it off by holding down the power button; this time it came right up. Shut it down normally again, it wouldn't turn on.

Power supply or something else? I do hear a slight buzz that may be coming from the power supply. I have seen @tsialex post about many Mac Pro issues being due to the power supply; I'm leaning that way.

From what you wrote is usually the PSU, probably damaged capacitors on the primary.

Did you have a known working PSU to install and confirm?

 

[HKSig]

From what you wrote is usually the PSU, probably damaged capacitors on the primary.

Did you have a known working PSU to install and confirm?

I do; maybe more than one. I'll have to dig one out from a pile. Thanks for the reply.

 

[dataid]

I have a friend's Mac Pro visiting due to problems. The description was "it won't turn on, then sometimes turns on by itself."

It did something similar here; after various troubleshooting (aka the service manual, pulling out/disconnecting everything), I did get it to come on. I found that if I unplugged it for ~48 hours, then plugged it back in, it would turn on normally. If I shut it down normally, it wouldn't turn on. Unplug for ~48 hours, turn it on, it was fine. I turned it off by holding down the power button; this time it came right up. Shut it down normally again, it wouldn't turn on.

Power supply or something else? I do hear a slight buzz that may be coming from the power supply. I have seen @tsialex post about many Mac Pro issues being due to the power supply; I'm leaning that way.

I had a very odd problem with my 2010 Mac Pro 5,1. It would occasionally not power on, sometimes after I got it to power on I could not power it off from the front power switch. Sometimes only after multiple presses on the power switch it would turn on. Of course it would power off after pulling the power cord. Of course this problem occurred randomly. After re-examining my software and OS I concluded that there was no software issue. I got a quote from a local computer service center to service the machine for $800. I decided that before I would junk the machine or replace the power supply I would do some basic trouble shooting, examine the hardware and use the little experience I had in assembling personal computer systems. I suspected an issue with the power system. I started trouble shooting guided by Apple's Technician Guide which can be found on the internet. The power supply tested out okay.

The long and short of the story is that I took out all major components and inspected connectors and reseated them and re-tested sequentially. The problem turned out to be the front panel power switch connector. When I first looked at the front power switch connector there was a tiny bit of gold shining in a nearly impossible to see gap between the male power switch connector and the connector on the small PC board it plugs into on the front of the machine. I wasn't even certain I could see the gap with my bare eyes. I took out my phone and using the camera's magnifying feature, confirmed that there was a tiny gap. I thought to myself that this could not possibly be the issue but went ahead and disconnected and re-seated the front power switch connector. I immediately tested the computer system.

The machine is still working properly to this day.

 

[HKSig]

The problem turned out to be the front panel power switch connector. When I first looked at the front power switch connector there was a tiny bit of gold shining in a nearly impossible to see gap between the male power switch connector and the connector on the small PC board it plugs into on the front of the machine. I wasn't even certain I could see the gap with my bare eyes. I took out my phone and using the camera's magnifying feature, confirmed that there was a tiny gap. I thought to myself that this could not possibly be the issue but went ahead and disconnected and re-seated the front power switch connector. I immediately tested the computer system.

The machine is still working properly to this day.

That was my first thought too: the board or the button. That would have been much easier than the power supply (two of the screws are tough to get to, and the thread locker doesn't help).
But, it does appear to be the power supply. It started up twice just fine with the donor power supply.