Resolved Mac Pro Hardware Problem - Looking for Some Insight

[Valdaquendë]

I'm new to MacRumors; this is my first posting. I've read the FAQ but if I'm doing anything wrong, here, please forgive and correct me. Thanks!

The other night a power problem in my office took out my Mac Pro; it appears to have been a defective UPS, of all things. The system is:

Mac Pro 5,1 (Mid-2010)
A1289 (EMC 2314)
3.33GHz HexCore (Westmere)
16GB RAM, 512MB SSD (+3 4TB drives)

I came in to find that the Mac Pro, while appearing to run (lights, fans, etc.) had no display output and was unresponsive to system devices (could not eject optical drive trays, for example). Checked and found that the UPS was malfunctioning. I have been following the diagnostic procedures in the Apple service manual (which I found at www.tim.id.au – an invaluable resource, for those working on the systems covered there) and am hoping for confirmation and information from those with more experience. I pursued the following diagnostic path:

1) I connected the system to known-good power; same behavior as above. I put it on the bench, got out the service manual and checked the diagnostic path. When the power button was pressed, the system fans and drives spun up normally. The front panel power LED lit up without flashing. The Processor Error LED on the processor board lit momentarily, as is normal. The display remained dark but gradually became populated with fine, green vertical lines. There was no startup chime nor any sign that input devices had any effect.

2) I performed an SMC reset; I attempted to perform a PRAM reset but, again, no input devices appeared to be effective. I know of no way to reset the PRAM on a system that won’t boot to the grey Apple splash screen, since the Cmd-Opt-P-R key combination does not work short of this stage.

3) Performing the minimal hardware procedure, I found that with the system completely stripped (only the power supply connected to the logic board), when the power cord was connected:
• OVTMP CPUA and OVTMP CPUB LEDs light for .5 seconds
• 5V STBY LED lights green when the DIAG button is pressed
So it appears the system is getting power and that the PSU is at least nominally OK.
(these are the expected results)

4) The next step in the minimal hardware procedure is connecting the processor board. Per the procedure, I removed the RAM, the heat sink and the CPU from the board and installed it. The procedure, at this point, specifies that you need to short across the SYS_PWR solder pads to power up the system, at which point the PSU PWROK (green), 5V STBY (amber), EFI DONE (green) and GPU OK (green) LEDs should illuminate and the processor cage fans should spin slowly.

4a) I found, however, that once the board was installed, the instant the power cord was connected, the fans started spinning slowly. Neither the power button nor the front panel board were connected to the logic board, nor was I shorting across the power-on solder-pads to make this happen. All these steps were performed a few days ago; at this point, I had to drop my investigation to attend to other matters.

4b) Then, this morning, I performed the procedure again and found that that the behavior has changed; now when I connect the components as described above, I have to short across the solder pads for the system to power up. In both cases (before and today), when power is connected:
• OVTMP CPUA and OVTMP CPUB LEDs light for .5 seconds
• 5V STBY LED lights green when the DIAG button is pressed
• PSU PWROK (green), 5V STBY (amber), EFI DONE (green), GPU OK (green) LEDs illuminate
• Fans spin slowly
(these are the expected results)

5) At this point, I connected the front board so I wouldn’t have to short across the pads each time, reinstalled the CPU and its heat sink and 1 DIMM (in Slot 1). The system powered up with:
• a brief flash of the processor error LED on the processor board.
• a chime 10 seconds after power-up
(these are the expected results)

6) Then I connected a hard drive with Mac OS 10.11.6 on it. It is a solid state drive, so I could not hear it spin up. Powered up with:
• System chime after 11 seconds
• Optical Audio Out port lit up after 27 seconds or so which, the manual indicates, is a sign of driver load. The manual says the port should light “shortly after start”; it lights 27 seconds after pushing the power button and 16 seconds after the system chime.
When the DIAG button was pushed:

• SYS_PG LED was lit
• EFI_DONE LED was lit
(these are the expected results)

7) The next step was to connect a graphics card and display. I had feared that my cinema display had been damaged (power-related damage can be widespread) and tried connecting it to a MacBook Pro with a Display Port; it worked perfectly, so I know the display is still good. I have no GPU except the one that was in the system (an ATI Radeon HD 5780/1GB) when the event occurred, so was unable to use the swap-out technique for this step.
When I connected the GPU and started up:
• nothing on the display
• a system chime EVERY 3.5 SECONDS or so – faint but perceptible.
Also,when the DIAG button was pressed:
• SYS_PG LED was lit
• EFI_DONE LED was not lit
• GPU OK LED was lit

8) The final step I could perform was to move the GPU to PCI Slot #2 to see if the problem was defective backplane circuitry at PCI Slot #1. The results were exactly the same as shown in Step 7.

Interestingly, if the system has been shut down for awhile, the first time or two that it is powered up, there is only one system chime; all other symptoms are as shown. After the first couple of power-ups, though, it starts recursively chiming as described above. My guess is that this is caused by capacitor(s) that are not fully charged the first time or two and discharge after power-down or something of the sort but I may well be wrong here and would be glad of any correction or insight.

My questions are these:
1) Can you think of any reason for the behavioral change between Steps 4a and 4b? Is it significant?
2) The GPU appears to clearly be at fault. Should I be worried about the backplane as well?
3) Is there a way to reset PRAM when the system won’t boot to the splash screen?
4) What would be your recommendations for “best” or “close-to-best” graphics cards?
5) Are there any concerns or aspects I’ve overlooked and, if so, what are they?

I realize that this has been a long and, perhaps, tedious posting. I want to sincerely thank you for reading and considering it. And thanks in advance for any insight, words of wisdom or corrections you may have to offer. I really appreciate them.

 

[startergo]

" Shut down your Mac, then turn it on and immediately press and hold these four keys together: Option, Command, P, and R. You can release the keys after about 20 seconds, during which your Mac might appear to restart.

• On Mac computers that play a startup sound, you can release the keys after the second startup sound."

I would just wait 3 chimes

 

[AlexMaximus]

I'm new to MacRumors; this is my first posting. I've read the FAQ but if I'm doing anything wrong, here, please forgive and correct me. Thanks!

The other night a power problem in my office took out my Mac Pro; it appears to have been a defective UPS, of all things. The system is:

Mac Pro 5,1 (Mid-2010)
A1289 (EMC 2314)
3.33GHz HexCore (Westmere)
16GB RAM, 512MB SSD (+3 4TB drives)

I came in to find that the Mac Pro, while appearing to run (lights, fans, etc.) had no display output and was unresponsive to system devices (could not eject optical drive trays, for example). Checked and found that the UPS was malfunctioning. I have been following the diagnostic procedures in the Apple service manual (which I found at www.tim.id.au – an invaluable resource, for those working on the systems covered there) and am hoping for confirmation and information from those with more experience. I pursued the following diagnostic path:

1) I connected the system to known-good power; same behavior as above. I put it on the bench, got out the service manual and checked the diagnostic path. When the power button was pressed, the system fans and drives spun up normally. The front panel power LED lit up without flashing. The Processor Error LED on the processor board lit momentarily, as is normal. The display remained dark but gradually became populated with fine, green vertical lines. There was no startup chime nor any sign that input devices had any effect.

2) I performed an SMC reset; I attempted to perform a PRAM reset but, again, no input devices appeared to be effective. I know of no way to reset the PRAM on a system that won’t boot to the grey Apple splash screen, since the Cmd-Opt-P-R key combination does not work short of this stage.

3) Performing the minimal hardware procedure, I found that with the system completely stripped (only the power supply connected to the logic board), when the power cord was connected:
• OVTMP CPUA and OVTMP CPUB LEDs light for .5 seconds
• 5V STBY LED lights green when the DIAG button is pressed
So it appears the system is getting power and that the PSU is at least nominally OK.
(these are the expected results)

4) The next step in the minimal hardware procedure is connecting the processor board. Per the procedure, I removed the RAM, the heat sink and the CPU from the board and installed it. The procedure, at this point, specifies that you need to short across the SYS_PWR solder pads to power up the system, at which point the PSU PWROK (green), 5V STBY (amber), EFI DONE (green) and GPU OK (green) LEDs should illuminate and the processor cage fans should spin slowly.

4a) I found, however, that once the board was installed, the instant the power cord was connected, the fans started spinning slowly. Neither the power button nor the front panel board were connected to the logic board, nor was I shorting across the power-on solder-pads to make this happen. All these steps were performed a few days ago; at this point, I had to drop my investigation to attend to other matters.

4b) Then, this morning, I performed the procedure again and found that that the behavior has changed; now when I connect the components as described above, I have to short across the solder pads for the system to power up. In both cases (before and today), when power is connected:
• OVTMP CPUA and OVTMP CPUB LEDs light for .5 seconds
• 5V STBY LED lights green when the DIAG button is pressed
• PSU PWROK (green), 5V STBY (amber), EFI DONE (green), GPU OK (green) LEDs illuminate
• Fans spin slowly
(these are the expected results)

5) At this point, I connected the front board so I wouldn’t have to short across the pads each time, reinstalled the CPU and its heat sink and 1 DIMM (in Slot 1). The system powered up with:
• a brief flash of the processor error LED on the processor board.
• a chime 10 seconds after power-up
(these are the expected results)

6) Then I connected a hard drive with Mac OS 10.11.6 on it. It is a solid state drive, so I could not hear it spin up. Powered up with:
• System chime after 11 seconds
• Optical Audio Out port lit up after 27 seconds or so which, the manual indicates, is a sign of driver load. The manual says the port should light “shortly after start”; it lights 27 seconds after pushing the power button and 16 seconds after the system chime.
When the DIAG button was pushed:

• SYS_PG LED was lit
• EFI_DONE LED was lit
(these are the expected results)

7) The next step was to connect a graphics card and display. I had feared that my cinema display had been damaged (power-related damage can be widespread) and tried connecting it to a MacBook Pro with a Display Port; it worked perfectly, so I know the display is still good. I have no GPU except the one that was in the system (an ATI Radeon HD 5780/1GB) when the event occurred, so was unable to use the swap-out technique for this step.
When I connected the GPU and started up:
• nothing on the display
• a system chime EVERY 3.5 SECONDS or so – faint but perceptible.
Also,when the DIAG button was pressed:
• SYS_PG LED was lit
• EFI_DONE LED was not lit
• GPU OK LED was lit

8) The final step I could perform was to move the GPU to PCI Slot #2 to see if the problem was defective backplane circuitry at PCI Slot #1. The results were exactly the same as shown in Step 7.

Interestingly, if the system has been shut down for awhile, the first time or two that it is powered up, there is only one system chime; all other symptoms are as shown. After the first couple of power-ups, though, it starts recursively chiming as described above. My guess is that this is caused by capacitor(s) that are not fully charged the first time or two and discharge after power-down or something of the sort but I may well be wrong here and would be glad of any correction or insight.

My questions are these:
1) Can you think of any reason for the behavioral change between Steps 4a and 4b? Is it significant?
2) The GPU appears to clearly be at fault. Should I be worried about the backplane as well?
3) Is there a way to reset PRAM when the system won’t boot to the splash screen?
4) What would be your recommendations for “best” or “close-to-best” graphics cards?
5) Are there any concerns or aspects I’ve overlooked and, if so, what are they?

I realize that this has been a long and, perhaps, tedious posting. I want to sincerely thank you for reading and considering it. And thanks in advance for any insight, words of wisdom or corrections you may have to offer. I really appreciate them.

Wow, this is very detailed. It almost goes down to a component level repair diagnostic.
The only real great repair entity that I know is this guy here on YouTube. He does repairs on the component level for Macbooks and stuff. I am sure he can help, the question remains how expensive will it be and does he work on Mac Pro's. It looks to me he is focused on macbooks.
Anyway here is the link, a phone call will help you out for sure to evaluate options.

https://www.youtube.com/user/rossmanngroup/

To your Questions:

1) No
2) Unknown at this point
3) I don't know
4) AMD Radeon 580 Pulse (no boot screens, OSX only + Mojave Support)

5) As an electrical engineer myself, a defect UPS as described can cause a short circuit which can backfire high power currents back through your mac power supply and grill it. (this can happen when led battery plates are eaten up and fall down to shorten the entire cell on the bottom, inside the module) However usually modern UPS systems are equipped with emergency lightning protection to prevent damage to the plugged-in device they power. (depends on the age of your UPS and brand) There are guarantees and coverages available. Some name brands lure customers with 5, 10 years and longer guarantees. If so they are on the hook. You may also check with your standard household insurance. They might cover some damage because of lightning and overcurrent events such as yours.
The green lines indicate a grilled GPU, a damage to other components is not entirely out of the question.

 

[tsialex]

If I was diagnosing this, I'd start testing the GPU then the backplane. You can test your GPU with a PC, but for the backplane you will need another Mac Pro.

Usually when you have a corrupted BootROM or problems with the SPI flash, the EFI done LED remains off. This is the most important clue.

I'm almost betting that your backplane is shot, if it was working and only the GPU was damaged, after you removed the GPU, Mac Pro would boot as usual and you could access it via network shares and screen sharing.

 

[Valdaquendë]

Wow; thanks, friends, for the prompt and informative replies!

startergo, as I said, I couldn't perform the PRAM reset but I had the GPU installed when I did it. I'm doing some work for two different clients, this morning, but when I have a chance, I'll remove the GPU and attempt a PRAM reset with it out. Weirdly, I did not think to remove the GPU and attempt it; but then back then at (4a), it looked like a processor board problem.

AlexMaximus, thanks for the advice; I'll keep your GPU recommendation in mind. And thanks for the info about UPS's. Mine is an APC and their warranty is a good one, as read; this will be my first chance to test it, though.

tsialex, thanks for that awesome suggestion! I hadn't thought to simply remove the GPU and use networking to see if I have proper boot-up ... but I WILL do it this afternoon! I can't believe that, after doing this sort of work for over 25 years, that didn't occur to me! Apparently, the obvious sometimes eludes me. Thanks a million!
[doublepost=1541621047][/doublepost] tsialex - Bless you, again, my friend!
I had a moment between clients and used it to remove the GPU, connect a network cable (the system is still stripped pretty bare; no WiFi, BT, ODD, etc.) and booted it up. I can login, screen-share, open resources ... everything looks good. I had some pretty significant video-artifacting, at first, but this was due to the number of apps I had had open before the fault and the fact that I had only one DIMM installed, so the system was trying to launch, run and display everything from available RAM (one 4GB DIMM). Once I quit the apps, the system behaved quite normally.

So now it's off to "New GPU" land ...

startergo - Once I ascertained that it could boot, I did, indeed, perform a PRAM reset, letting it chime 4 times. (hey; I know that 'third chime's a charm', but ...). The chime has been weak in volume up to now; upon the second PRAM reset, it regained its usual volume and everything seems to be normal. Thanks, again, for the advice.

Question - In my work on PC's (the vast bulk of my work, though my office and life run on Macs - you have to go where the work is and being a Mac tech is a lot like being the fabled Maytag repair guy), I have come to vastly prefer nVidia GPU's (and the awesome support that nVidia gives them) to ATI/AMD. I know that Macs can run nVidia cards (with certain caveats) and have started reading the 119-page forum thread on this topic. I am definitely going to check out AlexMaximus' recommended GPU; do any of you have advice or recommendations for an nVidia GPU or other GPU's in this context?

Again, thanks to all of you!

 

[startergo]

Wow; thanks, friends, for the prompt and informative replies!

Question - In my work on PC's (the vast bulk of my work, though my office and life run on Macs - you have to go where the work is and being a Mac tech is a lot like being the fabled Maytag repair guy), I have come to vastly prefer nVidia GPU's (and the awesome support that nVidia gives them) to ATI/AMD. I know that Macs can run nVidia cards (with certain caveats) and have started reading the 119-page forum thread on this topic. I am definitely going to check out AlexMaximus' recommended GPU; do any of you have advice or recommendations for an nVidia GPU or other GPU's in this context?

Again, thanks to all of you!

I would not recommend NVIDIA card for anything greater than High Sierra 10.13.6. So if you want to use Mojave stick to these recommended cards:

The Apple third-party graphics cards list identifies specific cards that are compatible:

• MSI Gaming Radeon RX 560 128-bit 4GB GDRR5
• SAPPHIRE Radeon PULSE RX 580 8GB GDDR5
• SAPPHIRE Radeon HD 7950 Mac Edition
• NVIDIA Quadro K5000 for Mac
• NVIDIA GeForce GTX 680 Mac Edition

The three cards listed in bold above have Mac EFI.
The list also identifies cards that might be compatible, none of which have Mac EFI:

• AMD Radeon RX 560
• AMD Radeon RX 570
• AMD Radeon RX 580
• AMD Radeon Pro WX 7100
• AMD Radeon RX Vega 56
• AMD Radeon RX Vega 64
• AMD Radeon Pro WX 9100
• AMD Radeon Frontier Edition

MP5,1: What you have to do to upgrade to Mojave
https://forums.macrumors.com/threads/mp5-1-what-you-have-to-do-to-upgrade-to-mojave.2142418/

 

[Valdaquendë]

I looked those over, startergo; thanks for the list and links. They really helped me clarify my choices. A number of the cards listed at everymac and elsewhere are difficult or impossible to find. Here are my thoughts:

I've been using the HD 5870 that came with my system but I've never been thrilled with it. I noted that, in high-performance situations, it had a tendency to punk out; I occasionally play an MMO, for example, that actually crashed the card at its highest settings. I'd like something with more horsepower and, considering the future, something with enough capacity to comfortably last for a few years.

I seriously considered the three EFI-equipped cards you listed but found that, with the exception of the Sapphire 7950, their benchmark scores are little better than my existing ... well, former ... GPU; using this videobenchmark chart as a guide (and recognizing that no such chart is perfect), these cards score:

Radeon HD 5870 - 2,619
K5000 Mac - 2,593
GTX 680 Mac - 3,351
Sapphire 7950 - 4,765

The RX 580, on the other hand, (which you seem to be using, yourself) scores a much-higher 8,431; not as high as the GTX 970, which scores 8,600, but still a very substantial increase and close enough for a Mojave-compatible card. I'm thinking that this would afford me high performance now and for the foreseeable future, as well as compatibility, for now at least.

I am a bit concerned, as I've seen one or two recommendations that nVidia, rather than Radeon, be used when using Adobe CC apps, which I use extensively, but they seemed to run reasonably on the HD 5870 and I'm willing to trust that they will on the new card.

I don't dual-boot or use Boot Camp; I work with hundreds of PC clients but I use VMWare Fusion, when I need access to the Windows environment on my system and remote access when I need access to theirs, so a non-EFI card seems a reasonable choice. I thought that, if I found a needed to access the boot options screen, I might use a solution like that used by Dr. Stealth, on this forum, who used a GT120 card to provide access to boot screens.

If you (or anyone) have any thoughts, insights or warnings, I'd be most grateful for them. And thanks again, to everyone, for the advice and insight!

P.S. - I don't want to be a bad forum member. If I should be reposting this as a fresh topic elsewhere, don't hesitate to tell me; I'll be glad to do so.

 

[startergo]

I looked those over, startergo; thanks for the list and links. They really helped me clarify my choices. A number of the cards listed at everymac and elsewhere are difficult or impossible to find. Here are my thoughts:

I've been using the HD 5870 that came with my system but I've never been thrilled with it. I noted that, in high-performance situations, it had a tendency to punk out; I occasionally play an MMO, for example, that actually crashed the card at its highest settings. I'd like something with more horsepower and, considering the future, something with enough capacity to comfortably last for a few years.

I seriously considered the three EFI-equipped cards you listed but found that, with the exception of the Sapphire 7950, their benchmark scores are little better than my existing ... well, former ... GPU; using this videobenchmark chart as a guide (and recognizing that no such chart is perfect), these cards score:

Radeon HD 5870 - 2,619
K5000 Mac - 2,593
GTX 680 Mac - 3,351
Sapphire 7950 - 4,765

The RX 580, on the other hand, (which you seem to be using, yourself) scores a (relatively) whopping 8,431; not as high as the GTX 970, which scores 8,600, but still a very substantial increase and close enough for a Mojave-compatible card. I'm thinking that this would afford me high performance now and for the foreseeable future, as well as compatibility, for now at least.

I am a bit concerned, as I've seen one or two recommendations that nVidia, rather than Radeon, be used when using Adobe CC apps, which I use extensively, but they seemed to run reasonably on the HD 5870 and I'm willing to trust that they will on the new card.

I don't dual-boot or use Boot Camp; I work with hundreds of PC clients but I use VMWare Fusion, when I need access to the Windows environment on my system and remote access when I need access to theirs, so a non-EFI card seems a reasonable choice. I thought that, if I found a needed to access the boot options screen, I might use a solution like that used by Dr. Stealth, on this forum, who used a GT120 card to provide access to boot screens.

If you (or anyone) have any thoughts, insights or warnings, I'd be most grateful for them. And thanks again, to everyone, for the advice and insight!

According to Adobe Photoshop graphics processor :
Which graphics cards are tested?
Tested cards
Adobe has tested the laptop and desktop versions of the following graphics processor card series:

• nVidia GeForce: 400, 500, 600, 700 series
• nVidia GeForce GTX 965M & 980M
• nVidia Quadro: 2000, 4000 (Windows® and Mac OS), CX, 5000, 6000, K600, K2000, K4000, K5000 (Windows® and Mac OS), M4000, M5000, P2000, P4000, P5000
• nVidia GRID K1, K2
• AMD/ATI Radeon: 5000, 6000, 7000, R7, R9 series, 7950 Mac OS
• AMD/ATI FirePro: 3800, 4800, 5800, 7800, 8800, 9800, 3900, 4900, 5900, 7900, W8100, W9100, D300, D500, D700
• AMD/ATI FireGL: W5000, W7000, W8000
• AMD RX 480
• nVidia GeForce 1080 GTX
  
• Intel® HD Graphics: P530, P630, 5000, 515, 520
• Intel® Iris Pro Graphics: P5200, P6300, P580
• Intel HD Graphics 515 and 520

Caution:

Tested cards may not meet the minimum bar for use with all GPU features. In addition to basic functionality, some Photoshop features, especially those which use APIs like OpenCL, require greater bandwidth, memory, or compute resources than other Photoshop features. These requirements can pose significant challenges when cards are placed in older machines, such as ones with low-powered motherboards or machines that make use of a single DIMM for their system memory, effectively halving the bandwidth between the system memory and the GPU memory.

Additionally, the relevant tests are performed when Photoshop starts up. On computers barely meeting the requirements, other running software may tip the balance from a card passing to failing. At times, OS updates, patches, and driver updates may cause issues with cards that were previously working fine.

We recommend you use the latest system and GPU hardware to make the most of GPU features in Photoshop.

Mine is actually RX-580 DELL OEM card, which is fitting perfectly in the 1st PCIE dual slot without any interference with the devices in the second slot as the regular RX-580 Sapphire Pulse does, which is 2.2 slots wide.
Maybe somebody else will provide you with more options.
[doublepost=1541644003][/doublepost]There is actually another one relatively cheap
https://www.bhphotovideo.com/c/prod...ml?kw=AMWX7100&ap=y&smp=y&BI=5451

Which is openCL and is recommended for Adobe premiere pro CC
https://helpx.adobe.com/premiere-pro/system-requirements.html

 

[Valdaquendë]

Thanks, startergo; I was going to check Adobe's site this evening ... and should have before I posted; it's been a long day.

The RX480 looks quite good but, of course, is not on the Mojave compatibility list. The 580, on the other hand, is listed as a 'might work'. I'll keep digging and will report back to this thread with whatever I wind up with and whether/how well it works. Are you running Mojave? If so, how is it working for you?

Thanks so much!

 

[Valdaquendë]

I have to retract my initial assessment, on Wednesday, that the system works "quite normally". It does ... but only over a network connection and only to a degree.

At that time, the system was still largely stripped, as described in my last post on Wednesday. Yesterday, I installed the remaining components, booted up the system and connected a keyboard and mouse (up to to that time, I had been controlling the system using Network Sharing). I found that, while the keyboard seems to function normally, the mouse does not.

Mouse & Cursor
Moving the mouse does not cause the cursor to move on the screen, nor is there screen display of the click-drag marquee. The system IS cognizant of mouse movement and clicks; if I move the mouse and click, any object that happens to be under its current location will be selected and moving the mouse down and to the left, for example, and then clicking will select any object that happens to be in that relative position. The system clearly knows and tracks the mouse's position and responds to actions like clicking, double-clicking and right-clicking ... but the cursor does not move.

Further, no click-and-drag action is functional; placing the cursor (using Network Sharing) above and to the left of one or more objects and then click-dragging (with the mouse connected to the MP) down and to the right will not result in selection of the object(s). I have tried this with both a USB mouse and a BlueTooth mouse; both behave in the same way, whether booted normally or in Safe Boot mode.

I ran TTP, which found no problems (other than a few files with file-structure errors). Then, to determine whether the problem was at the operating system level (corrupted OS, etc.), I replaced my OS drive with a mirror drive created some months ago; one known to have no problems. The behavior remains the same, indicating that the problem is at a deeper level.

Other Oddities
There are some other odd behaviors as well; the 'About this Mac' window will only appear every SECOND time its alias is selected from the Apple menu. When it does, it's 'Overview' panel is blank until I click on another button ('Displays', 'Storage', etc.) and then click back on 'Overview'. The 'Displays' panel behaves the same way. The 'Overview' panel's 'Startup Disk', 'Graphics' and 'Serial Number' fields are not populated, though this data does show up in the System Profiler.

The Next (and perhaps Last) Step
The only remaining potentially effective diagnostic or recovery procedure I can think of is to perform is a firmware reinstall since, according to this Wikipedia article, the EFI firmware controls the rudimentary pre-boot GUI framework, including support for image drawing, mouse cursor and more. I'm not sure, however, whether a firmware update can safely be performed in the absence of a graphics card or display; the one thing I DON’T want is a problem in the middle of a firmware update, since that would trash the backplane. Has anyone tried this? Perhaps I should possess myself of patience and order and await the delivery of a replacement GPU.

I might mention, parenthetically, that Apple’s support page illustrates all EFI updates after the 1.1 update (for 2009 cMP’s) with the cylindrical ‘trash can’ Mac Pro (nMP), even though they clearly predate that form factor. The latest firmware update for my system (Mac Pro 5,1), is posted HERE.

If you have any other suggestions or insights I'd be grateful. In the meantime, I'm going to start looking for replacement backplanes. I'll be checking various Mac vendors, as well as eBay, etc. Any words of wisdom?

And my very sincere thanks for the help and advice you have given me. I appreciate it and will pass your generosity on by helping others in the MacRumor forums.
[doublepost=1541796674][/doublepost]I wanted to update you, startergo, with regard to GPU's. At this point, I'm leaning heavily toward the Radeon PULSE 580 8GB. Of the cards listed by Apple as Metal2 and Mojave-compatible, it has far and away the highest benchmark scores and, according to MVP's on Adobe's forums, it will easily run CC apps. If you have any thoughts, I'd welcome them.

 

[Valdaquendë]

It is now December, 2021, three years since I started this thread. At the time, I was a MacRumors newbie and didn't know about marking your threads as 'Resolved' and, in the hurly-burly of the events occurring at that time, I left this thread dangling. Trying to become a better forum citizen, I thought I'd update this and the other threads I've started.

UPDATE: I did, in the end, purchase and install the Radeon Rx 580 PULSE. It has worked very well and handled everything I could throw at it with ease. I do a good deal of work in Adobe Illustrator, InDesign and Photoshop and I play an MMO (Lord of the Rings Online) during those fleeting moments that I can make available to do so. It has handled all of these activities (at the highest possible graphics settings, in the case of LOTRO) with aplomb.

At that time (2018), I went through the entire machine and discovered, to my dismay, that one of the pins on backplane's CPU tray socket was missing. The system runs quite well, though it does, sometimes, behave oddly when you pull down a menu (the 'Recent Items' menu for example). Then it pauses, with spinning beach-ball, for about 15 seconds before displaying the menu. (I have tried cloning the system drive and putting it in the system mentioned below and found that this behaviour does not occur, which suggests that the problem may be in hardware.)

This system (the subject of this thread) has been my office workhorse and at the time of this thread I had had it down so long that I couldn't spare it any longer. I just got (and am completely refurbishing) a 2012 12-core Mac Pro and, when I get that system up and running, I'll switch to it and tear this one down, go through it completely and replace its backplane.

A belated but very sincere thanks to Startergo, AlexMaximus and tsialex for your help and counsel during that adventure.