MP 1,1-5,1 Same old problem: Mac Pro 4,1 -> 5,1 won't turn on (sometimes) and random shutdowns

[Sartolo]

Hi everyone,
I've been lurking the forum for a while and now I'm looking for a solution to a problem that seems nobody on the internet has ever solved without replacing the motherboard, which I'd want to avoid as this Mac is a 0 budget project for me. I've recovered it 2 years ago literally from a dumpster and it wouldn't be worth it spending 80€+ on something I couldn't rely on anyway.

So, it's again the notorious MP 4,1 -> 5,1 problem: went good for months, then all of a sudden it couldn't wake up from sleep mode, and then (days later) the computer just won't turn on anymore unless after hours/days of rest, not being reliable at all and being affected by random shutdowns.

Thing I've tried swapping (almost everything):
- GPU (even tried PCIe slot 2 - seemed to work, nothing changed actually)
- PSU
- CPU tray
- tried connecting/disconnecting disc drive

Nothing of the given parts seemed to change anything, just like everything the Mac Technician's Guide suggests for these problems.

I've taken apart all the system just to discover the (in)famous white marks on the back of the backplane, followed that path (from some @Macschrauber posts) and desoldered the 3 capacitors around those areas that could have leaked. I've yet to replace them, but some more pictures I've found online show me that even known good motherboards have those marks - so with it being flux as @tsialex pointed out in one of them posts and not a capacitors' leakage (capacitors also test good after being desoldered).
It's also true that what makes the MP work after X hours is the discharge of the capacitors (as somebody in some threads pointed out - sorry I can't remember who wrote that), so I'm going to replace the capacitors anyway but with few hopes.

So what now? I'm not buying a replacement board, as this computer is somewhat a fun project to play with for me, so I'm open to suggestions about what I can try to fix it and have a working MP.
If it's not fixable in any possible way I'm probably going to sell parts like the PSU, the disc drive, the CPU tray and the GPU.

I'm also keeping this post updated just for the Google, as a lot of these topics have been left incomplete.

 

[tsialex]

First thing, I don't understand why you talk about MBP several times, you have a MBP or a Mac Pro?

The easiest, fastest and cheapest way to diagnose a Mac Pro is to test each component with a working Mac Pro and not the oter way around, like way you did. Your issue could be somewhere else instead of the backplane, even a defective front panel or a DVD drive could cause the issues you wrote.

Solid caps fail, but usually doesn't leak, almost all Mac Pro capacitors are polycon/solid, the purple band. Leaking caps residue is usually brownish or is tranparent and becomes brown after the pads are corroded. White residue is solder flux not completely cleaned at the factory, even brand new/NOS boards have it.

 

[Sartolo]

First thing, I don't understand why you talk about MBP several times, you have a MBP or a Mac Pro?

The easiest, fastest and cheapest way to diagnose a Mac Pro is to test each component with a working Mac Pro and not the oter way around, like way you did. Your issue could be somewhere else instead of the backplane, even a defective front panel or a DVD drive could cause the issues you wrote.

Solid caps fail, but usually doesn't leak, almost all Mac Pro capacitors are polycon/solid, the purple band. Leaking caps residue is usually brownish or is tranparent and becomes brown after the pads are corroded. White residue is solder flux not completely cleaned at the factory, even brand new/NOS boards have it.

MBP was a typo, I'm really sorry. Has been a long day.

I've tried removing DVD drive also, as well as trying to jump start the Mac having the front board disconnected.

 

[tsialex]

Did you tried to run ASD 3S149 when the Mac Pro works?

Also, did you tried to boot a Mavericks disk with the RTC battery disconnected, bypassing the BootROM NVRAM? BT/WiFi won't work, but it's a good test to see if the BootROM have or is causing any issue.

 

[Sartolo]

Did you tried to run ASD 3S149 when the Mac Pro works?

Also, did you tried to boot a Mavericks disk with the RTC battery disconnected, bypassing the BootROM NVRAM? BT/WiFi won't work, but it's a good test to see if the BootROM have or is causing any issue.

1. Nop, just because I can't manage to turn it on anymore 🥲 best I can do is turning it on without GPU and like 20% of the times, 80% it would shut down itself

2. No I did not, will try for sure

 

[tsialex]

1. Nop, just because I can't manage to turn it on anymore 🥲 best I can do is turning it on without GPU and like 20% of the times, 80% it would shut down itself

This is usually the PSU.

You should borrow/buy a working Mac Pro and test each component one by one and then eliminate any possibilities.

 

[Sartolo]

This is usually the PSU.

You should borrow/buy a working Mac Pro and test each component one by one and then eliminate any possibilities.

I already did that, I'm sorry if it's not clear from the first message.

I've put a known good PSU in the system and nothing has changed, literally nothing. No sign of life by any chance

 

[tsialex]

I already did that, I'm sorry if it's not clear from the first message.

I've put a known good PSU in the system and nothing has changed, literally nothing. No sign of life by any chance

Seems you didn't understood my point, the easiest way to test is to install one component of the defective Mac Pro in the working one. One at a time you do the elimination test. Installing a good component to a defective Mac Pro is not the best way and you could even damage the working part, being there done that.

 

[Sartolo]

Seems you didn't understood my point, the easiest way to test is to install one component of the defective Mac Pro in the working one. One at a time you do the elimination test. Installing a good component to a defective Mac Pro is not the best way and you could even damage the working part, being there done that.

Oh sorry. Didn't do that because I was worried a bad PSU (for example) could damage the working Mac. If that's not the case, I'll definitely try components one by one as well.

 

[Sartolo]

A brief update:
- changed those 3 capacitors around the white-ish area, long story short: nothing changed
- as I was reassembling the MP I went through the minimum configuration test once again, just because I was doubtful about having done the right procedure the first time. The behaviour was indeed a little funny: backplane in, PSU in, behaved as expected; as soon as I've attached the CPU cage/tray(no cpu/RAM/heatsink), power chord in, the pc spinned back to life by itself (no frontboard was connected). CPU board out again, nothing happens when connecting the plug; board in, same thing. I have a MP 5,1 (not 4,1 -> 5,1) to try swap components with, so I followed @tsialex instructions and I put 4,1 tray into 5,1, knowing that if powered on it would have gone full fans; it was just to see if MP 5,1 powered itself on with that tray. Guess what? Nothing happened lol. I've even turned it on, full power fans kicked in, nothing special to point out.
Got the tray back into the 4,1 (remember - no front board installed), nothing happened; tray/cage out, front board in, cage/tray in, nothing happened, MP doesn't turn on.

I've also done the Maverick's disk, but I don't know what to do with that as the problem seems to be more power related, but I can't understand in which way.

I've yet to try the PSU thing (4,1 PSU into the 5,1), I'll probably test that tomorrow.

Seems to me there's something wrong with the board, I'm 100% sure I'd solve the problem with a new backplane off eBay, but as I said I don't want to walk that path.

If you've got any other ideas or any other test I can make, I'll do that and keep you updated.

 

[macguru9999]

Its probably the backplane, of course. Its less than one hour's work to change it, but at this point i would just buy another mac pro and use the first one for spares. the prices have come down alot.

 

[Sartolo]

Its probably the backplane, of course. Its less than one hour's work to change it, but at this point i would just buy another mac pro and use the first one for spares. the prices have come down alot.

Yeah I know that, but I'm not interested in buying another backplane as I said in the first post.
I'm no expert in microsoldering (but I'm learning), more importantly I'm no expert in fault finding with multimeter and stuff like that. That's the reason why I'm posting here, hoping that somebody with way more expertise than me could come here and give me some advice in what could be done to that backplane to make it work again.

My sensation is that there's some shortcircuit somewhere, probably in the powering on circuit. That would explain why sometimes it just doesn't power on and even why sometimes it shuts off, as if someone was actually pressing the button.

I've read tons of posts online (here, in the Apple support website, reddit ecc) and nobody seems to have found the actual problem, which is quite peculiar as MP 4,1/5,1 are/were widely used all over the world, we're not talking about some niche product.

 

[macguru9999]

There are plenty of youtubes on troubleshooting and microsoldering, but those with the skills i have seen are working on macbooks... i have never seen one on mac pros. it would be almost impossible if you dont know where to start.

 

[Sartolo]

There are plenty of youtubes on troubleshooting and microsoldering, but those with the skills i have seen are working on macbooks... i have never seen one on mac pros. it would be almost impossible if you dont know where to start.

Totally agree.

Update: tried the PSU swap, guess what? The 4,1 PSU works like a charm when put in the 5,1.
So, that's not the PSU.

Pro: it's 100% something on the board, which is probably power-related, not sure if on the powering itself or on the circuit which powers the computer on.
Cons: it's 100% the board and nobody seems to know anything more lol.

Still open to suggestions.

 

[tsialex]

it's 100% the board and nobody seems to know anything more lol.

The issue resumes to the fact that the current replacement cost of the backplane is below the cost of any diagnostics, supplies, replacement parts.

While we still can get backplanes for sometimes $40 + shipping, no one will sit and even try to look something besides the most obvious defects, period.

Maybe in the distant future will have demand for that, like today Amiga boards have.

 

[Sartolo]

The issue resumes to the fact that the current replacement cost of the backplane is below the cost of any diagnostics, supplies, replacement parts.

While we still can get backplanes for sometimes $40 + shipping, no one will sit and even try to look something besides the most obvious defects, period.

Maybe in the distant future will have demand for that, like today Amiga boards have.

The point is I'm from Italy and the deals seems to be located 99% in the US, so shipping costs for me skyrocket easily.

I'm leaving this post here and bring some updates if I'll have some.
Thank you btw for your posts alex! Much appreciated.

 

[krakman]

In my personal experience I had 4 Mac Pros 4.1 and a 6.1 die from excess humidity.

I lived by the sea and the salty humid air caused problems.

The humidity was so high that the Apple store claimed I had split water into the computer!!!

My only suggestion is, buy a big bottle of isopropyl alcohol and a soft brush and give the backplane and CPU board a good wash to remove any dust/corrosion that may have accumulated around the components.

I too bought a new power supply only to discover the problem lies elsewhere!

In the end it was cheaper/easier to buy working computers on Ebay.

 

[Sartolo]

In my personal experience I had 4 Mac Pros 4.1 and a 6.1 die from excess humidity.

I lived by the sea and the salty humid air caused problems.

The humidity was so high that the Apple store claimed I had split water into the computer!!!

My only suggestion is, buy a big bottle of isopropyl alcohol and a soft brush and give the backplane and CPU board a good wash to remove any dust/corrosion that may have accumulated around the components.

I too bought a new power supply only to discover the problem lies elsewhere!

In the end it was cheaper/easier to buy working computers on Ebay.

It's a good point, I do have a big bottle of IPA, could be working on that this weekend maybe. The pc was in fact found in a wet environment (and covered in guano, fyi lol), I don't put much hope in this solution but it won't hurt it for sure.

I'm 100% sure it would be easier to buy a working backplane on eBay, but since this is a recovered MP and it's a sort of playground for me, I want to see if I can manage to learn something from it.

 

[MrScratchHook]

It's a good point, I do have a big bottle of IPA, could be working on that this weekend maybe. The pc was in fact found in a wet environment (and covered in guano, fyi lol), I don't put much hope in this solution but it won't hurt it for sure.

I'm 100% sure it would be easier to buy a working backplane on eBay, but since this is a recovered MP and it's a sort of playground for me, I want to see if I can manage to learn something from it.

yes, you will absolutely learn something........that's its a faulty backplane...
i KNOW,YOUR NOT INTERESTED IN A REPLACEMENT. The only other option is the trash im afraid.

 

[Sartolo]

yes, you will absolutely learn something........that's its a faulty backplane...
i KNOW,YOUR NOT INTERESTED IN A REPLACEMENT. The only other option is the trash im afraid.

That's not my kind of approach lol. As somebody says, "if ain't broke i'll fix it 'till it is" 😏

Updates: IPA didn't change a thing, as expected.
I'm thinking of discharging the capacitors, desoldering and testing every single one of them (they're not that much), could be something I will do in the next weeks.