4,1 Mac Pro, won't power on

[Morgan Mac]

So about two years ago I was playing a graphically intensive video game on my Mac Pro 4,1 computer. I was becoming slightly alarmed as I noticed the fans had automatically sped up to cool down the processor, it was getting very noisy. Then suddenly the display just went black. The processor was still running full speed. I shut the computer off at the mains not knowing what to do. Upon restart the monitor wouldn't show anything. I reduced the brightness using the keyboard shortcut and upon restart the display worked. From then on I realised the monitor would only display on reduced brightness (12 brightness increments out of 15 total).

Progressively this got worse over the months and had to lower the brightness more and more for anything to display. When it would work only under 3 brightness increments I purchased a better GPU on the presumption that was the issue. It didn't change anything. Doing more research online I opened up the 24" ACD monitor to inspect capacitors and wires. I bought a new Logic board for the ACD but again, no change. More recently, I bought a PSU for the processor but no change either.

At this point I'm running out of things to check. Recently the processor won't even power on anymore, which eliminates the ACD being the issue. I suspect now the issue is with the motherboard but only due to a process of elimination. What are your thoughts? I don't live in an area where I can swap identical Mac components with a friend or to deliver it to a repair shop to diagnose the problem professionally.

 

[Macschrauber]

Pull the GPU and try if the Mac boots.

 

[Morgan Mac]

Pull the GPU and try if the Mac boots.

It's the same result with the GPU and all unnecessary peripherals removed. The moment I switch the power on at the mains a red light blinks briefly inside near the power button. Indicating it is receiving power. But the processor doesn't kick into action when the power button is pressed. Occasionally the processor will start if I press power quickly after turning it on at the mains. But not enough juice so that the ACD also springs to life.

 

[Macschrauber]

I do not understand the ACD thing. Those are 2 complete different pieces of Hardware, your Monitor and your Computer. If you think your Display is broken get another one, or even a TV with HDMI Input. The Issues sound like it's being a PSU Problem on the Mac - but you already replaced the PSU in the Mac ? With a known good one ?

 

[Morgan Mac]

I do not understand the ACD thing. Those are 2 complete different pieces of Hardware, your Monitor and your Computer. If you think your Display is broken get another one, or even a TV with HDMI Input. The Issues sound like it's being a PSU Problem on the Mac - but you already replaced the PSU in the Mac ? With a known good one ?

The Apple Cinema Display uses a mini display port connection. So I can not substitute with a HDMI TV or traditional PC monitor. Buying a new ACD is costly as I'm sure you are aware. In my previous post I mentioned the ACD only as further evidence that either the processor or monitor are the issue.

I purchased a brand new PSU from an eBay seller for 115€ + 40€ delivery costs. I made it known to the seller before buying that I was unsure the PSU was what I needed and he gladly refunded me upon returning. It behaved the exact same as my current PSU.

 

[JedNZ]

See one of my recent posts - looks like I cooked one of my CPUs. So it could be that, but I’d wage a bet it’s something to do with your Northbridge heatsink or rivets. Check to see if there is enough heatsink thermal paste and that the rivets haven’t perished. You’ll have to re- apply the thermal paste on CPU A - worth doing it anyway if it hasn’t been touched for years.

 

[Morgan Mac]

See one of my recent posts - looks like I cooked one of my CPUs. So it could be that, but I’d wage a bet it’s something to do with your Northbridge heatsink or rivets. Check to see if there is enough heatsink thermal paste and that the rivets haven’t perished. You’ll have to re- apply the thermal paste on CPU A - worth doing it anyway if it hasn’t been touched for years.

I like this suggestion. I've not considered the heatsink as to where the problem might be located until now. However I need to purchase a 3mm size extra long allen key to get in there. If I can't find it locally I might need to wait two months for an online delivery.

I'm still suspicious the issue might be with the motherboard. A replacement motherboard is very costly - 200-250€ on eBay. I contacted the sellers and they are not willing to allow me to return it with refund if it doesn't solve my technical issue.

 

[Morgan Mac]

I purchased a 3mm extra long allen key online but it will take several weeks to arrive. In the meantime I'm thinking of purchasing some plastic rivets for the heatsink because they are very cheap. They are intended for PC computers however.

Does this look like the same design and size (22mm)?

 

[Morgan Mac]

The 3mm extra long allen key arrived today. I used it to unscrew the heatsink and look underneath. It was fairly dusty under there, as expected. The Northbridge heatsink rivets are intact. There were many tiny black bug eggs and some small cobwebs. I wonder if they might have clogged or damaged a component.

I spent some time gently cleaning the whole board with tissues, a toothbrush, compressed air, and a tweezer. The board is now very clean. I will apply some fresh thermal paste tomorrow.

 

[JedNZ]

The state of the thermal paste has me worried. It looks dry and patchy, and those are two seriously concerning things. Looks like a bunny **** dust balls all over the heat sink lol. Looks like you’ve done a fine job cleaning up, so fingers crossed for the next stages and the eventual power-on!

 

[Morgan Mac]

Today I gently cleaned off the crusted thermal paste and applied some fresh paste.

While I was at it, I also removed the logic board and the small board that the front power button connects to and cleaned them thoroughly. So every part is clean now.

Alas, it changed nothing and the processor still won't power on!

 

[Frank DiMaulo]

Any luck? I had a similar problem when I stressed out my MP using FCP. Turned out to be CPU B not being fastened tight enough. The intermittent connection gave me the same symptoms.

 

[Morgan Mac]

@Frank DiMaulo No luck. I don't know what my next move is to be honest. It's not the PSU or the GPU or the memory, the power cable is fine, and the CPU is freshly greased. The main suspect right now is that the backplane board is faulty. But I am not going to drop a lot of money to purchase a brand new backplane board on a whim that it solve the issue. It will cost less to travel to a Mac repair store to hopefully receive a conclusive diagnosis on the source of the issue.

 

[Frank DiMaulo]

@Frank DiMaulo No luck. I don't know what my next move is to be honest. It's not the PSU or the GPU or the memory, the power cable is fine, and the CPU is freshly greased. The main suspect right now is that the backplane board is faulty. But I am not going to drop a lot of money to purchase a brand new backplane board on a whim that it solve the issue. It will cost less to travel to a Mac repair store to hopefully receive a conclusive diagnosis on the source of the issue.

I picked up a backplane board for my cMP for $150 from eBay. It had a 60 day return policy. Luckily my problem was different, point being its not so bad a job to replace. I've read about another person here who couldn't start up reliably and the backplane replacement fixed it. There is also a way to jump the solder pads at the on button to see if its just the switch. Here is the flow chart.

 

[Morgan Mac]

I picked up a backplane board for my cMP for $150 from eBay. It had a 60 day return policy.

Unfortunately for me the average backplane board is running $100 more than that due to import and delivery costs. Also none of the sellers allow returns - I checked with several of them.

There is also a way to jump the solder pads at the on button to see if its just the switch. Here is the flow chart.

I reread the technical manual again last week and "jumping the solder pads" was the only step that confused me. Thankfully there was an old thread on here where the question was asked and answered.

 

[Morgan Mac]

I went through the Minimum Configuration Testing procedure again attempting to jump the SYS_PWR solder pads each time. I had no success, even with everything out but the backpanel board connected to the power unit. But the 5V STBY LED lit up each time also. So the backpanel board is receiving power. So I believe the frontpanel board is in good condition. But maybe the backpanel board is damaged somewhere.

One thing I noticed is that there is discolouration on the line of solder pads, as if corroded by minor liquid damage. I'll clean the pads with Isopropyl alcohol and retest later this week.

 

[krakman]

This week I took three 4.1s out of winter storage as I'm preparing my office for my busy summer wedding season. Within days all there cMPs have failed, same problem as yours!!!!

Mac 1: Turned on - worked for 10 minutes then switched off - won't reboot, no sound from PSU when power cable connected!

Mac 2: Turned on - worked for 10 minutes then switched off - rebooted once then switched itself off - now won't reboot, clicking heard in PSU when power cable connected!

Update: wow! after several days of inactvity i pressed the power button of Mac 2 and it booted up and worked for about 2 hours then it switched itself off again - cannot reboot at the moment??? !!!!

Mac 3: Will boot but intermittently turns itself off after various period of time???

I have a new power supply on its way to test the systems.

 

[Cecco]

Was anyone of you successful in repairing your dead Mac Pros?

 

[Morgan Mac]

Was anyone of you successful in repairing your dead Mac Pros?

Sadly no, Cecco. But I am still working on bringing it back to life. I brought the motherboard and processor board into a computer retail and repair store last week. The guy had a close look at both boards and surmised that the motherboard looks fine. A minor bit of cosmetic damage around a small chip possibly to do with a spark from a short circuit. The processor board however - he took off the Northbridge chip to look for signs of damage. Then soldered it back in place. When I brought it back home it made no difference.

So the jury is still out. My suspicion is that there is subtle damage to the motherboard or processor board. That or the frontpanel board or cables are damaged. But I doubt it.

I don't know what my next move is right now. Any further suggestions are most welcome.

 

[Squuiid]

Sadly no, Cecco. But I am still working on bringing it back to life. I brought the motherboard and processor board into a computer retail and repair store last week. The guy had a close look at both boards and surmised that the motherboard looks fine. A minor bit of cosmetic damage around a small chip possibly to do with a spark from a short circuit. The processor board however - he took off the Northbridge chip to look for signs of damage. Then soldered it back in place. When I brought it back home it made no difference.

So the jury is still out. My suspicion is that there is subtle damage to the motherboard or processor board. That or the frontpanel board or cables are damaged. But I doubt it.

I don't know what my next move is right now. Any further suggestions are most welcome.

Buy a (cheap, low spec) replacement CPU off eBay perhaps?

 

[Morgan Mac]

Buy a (cheap, low spec) replacement CPU off eBay perhaps?

I have no reason to believe the CPU is the issue. It looks in good condition. And the backlight issue progressively became worse over almost a full year. I'm sure if the CPU was damaged, the computer would instantly become unusable.

 

[Cecco]

I'll probably try to reflash the BootROM. You may read my conversation here.

 

[Stux]

I take it you've looked at the LGA pins in the socket to ensure that none of them have been over-compressed? They should look uniform... if you see any which are casting light differently that might be it. I've recovered a macpro that this happened on by very carefully raising the compressed pins.

 

[Morgan Mac]

I take it you've looked at the LGA pins in the socket to ensure that none of them have been over-compressed? They should look uniform... if you see any which are casting light differently that might be it. I've recovered a macpro that this happened on by very carefully raising the compressed pins.

The LGA are the CPU socket pins? There is no reason to believe that might be the issue because I hadn't removed the CPU until the issue occurred, and it progressively got worse over many months. But I did have a close look at all the pins and they look as they should.

 

[Stux]

The LGA are the CPU socket pins? There is no reason to believe that might be the issue because I hadn't removed the CPU until the issue occurred, and it progressively got worse over many months. But I did have a close look at all the pins and they look as they should.

Yes, the Land Grid Array pins

Was just something worth checking