MP 1,1-5,1 Mac Pro 2009 suddenly shut down and won't start anymore

[caronte23]

Hi everyone, I have a mac pro 2009 running osx high sierra. I've had this since new, in 2019 I've upgraded the cpus with two delidded x5680s and 64Gb of ddr3 error correcting RAM, also updated the firmware from 4.1 to 5.1.
Never had an issue with it and temps ran great. Today it suddenly shut down while I wasn't doing any particularly tasking activities and now it won't boot anymore.
When I press the power button the power led breafly blinks once and then immediately shuts off again.
I had a look inside, when I try and power it a red led next to the cpu towards the back oc the case blinks twice.
I tried removing the graphics card (stock nvidia GT120) and the same issue persists.
One thing I can say is that as soon as it shut down by itself I opened the lid and touched the heat sinks to check the temperatures: the cpu towards the front of the case had normal warm temperature, the one towards the back was considerably hotter.
I also tried removing the power plug and waiting 15 seconds (is this how you reset the SMC?) but nothing changed.
I tried pressing the button next to the 5v battery but no led turns on.
I also tried removing the board with the cpus and powering it but in that case nothing at all happens, sat it back in and now is the same exact issue as before.
What else should I try and do? Do you guys have any idea what might have happened?

 

[reader50]

If you have a voltmeter, check the voltage on your BR2032 button battery. A reading below 3v would likely explain things. Alternatively, pull all the drives (including unplugging the optical drive) and see if you get the boot-prohibited symbol. A failed drive can hang boot.

BTW - your Mac Pro is a 2009 model.

 

[caronte23]

If you have a voltmeter, check the voltage on your BR2032 button battery. A reading below 3v would likely explain things. Alternatively, pull all the drives (including unplugging the optical drive) and see if you get the boot-prohibited symbol. A failed drive can hang boot.

BTW - your Mac Pro is a 2009 model.

You're right its a 2009 model, anyways I checked the battery, voltmeter reads 2.98V. Tried removing all the drives and optical drive, same issue.

 

[Borowski]

Too low. Exchange the battery, a CR2032 will also work.
Try a multiple NVRAM reset, hold keys alt-cmd-r-p while starting until the mac chimed 3 times.
You may also try to start without battery, this will override NVRAM content.

 

[caronte23]

Too low. Exchange the battery, a CR2032 will also work.
Try a multiple NVRAM reset, hold keys alt-cmd-r-p while starting until the mac chimed 3 times.
You may also try to start without battery, this will override NVRAM content.

Ok, I'll try and change the battery, are you sure that 2.98 is too low? It's a 3V battery after all...
I can't actually get to the point of interacting with a keyboard during boot. The machine turns off almost immediately after pressing the power button, maybe 1 second.

 

[Borowski]

Yes, the no-load voltage is higher. Mine has 3.2 volt.

 

[caronte23]

Yes, the no-load voltage is higher. Mine has 3.2 volt.

As soon as I can I’ll test with a new battery, but are you sure the symptoms I described are consistent with a dead battery?

 

[Macschrauber]

You can try a quick ab test without the battery. Machine should start without power on switch. Issues are expected, but thats just for a test run.

When the Mac boots and shut down after 1 or 2 minutes that could also be a headless OS problem for no compatible board or the forbidden sign, when displaying not verbose.