cMP 5.1 no chime, black screen, no POST

OK,
A few days ago my Mac Pro 4.1 > 5.1 from early 2009 froze on me while I was walking around in Photoshop on a Windows 10 partition. I had to do a hard reset after freezing . When resetting, nothing happened at first. It just hung there on a black screen. Rebooted again and successfully booted to select screen and back into Windows. Shortly after, it froze. Reset. Booted into MacOSX Mojave to see what happens. Freeze again a few minutes later.
Now I get nothing. No POST indication whatsoever. No chimes. Nothing. The machine turns on. The fans operate at normal frequency. But that’s all.

In the best interest of saving time and trying to make a speedy recovery out of it, as this cMP is my daily engine, I will dump as much as I know, have observed and what my the diagnosis is up to the time of this writing. In other words, I really need confirmation before I start spending money on this repair. Pretty much everything I’ve inferred about what’s going on here and a possible solution is pretty new to me. Stay with me. If there’s something glaring that I’m not seeing or if I’m making a horrible mistake somewhere, talk about it.

Specifications:
Early 2009 cMP 4.1>5.1 Dual Socket 3.46 GHz Intel Xeon 6 Core
32GB 1333MHz DDR3
1TB Sabrent Rocket Q NVMe PCIe M.2 2280 boot SSD + 2x 1TB stock Apple Mechanical HDD
AMD Radeon Pro Duo (Polaris) GPU

What is happening:
Mac turns on
No Apple Chime
Black screen
Fans run at normal frequency
Hard drives spin for a few seconds
No other POST sequence

What was done :
Removing hard drives one at a time in different models and slots and powering up with each removal model.
Remove accessories one by one (HDD, SSD, GPU, RAM ((one key at a time)), USB accessories, DVDRW, etc.) and reboot each time one was removed.
Replacing Radeon Pro Duo with the original NVIDIA GeForce GT 120, then powering up without any GPU.
CMOS battery removed and replaced with a new battery.
Checked CPUs for bent pins, uninstalls, or anything weird next to related components.
CMOS reset button pressed
Diagnostic button pressed following lights on:
-PSUPWROK
-SV STANDBY
-SYS PG
So far I’ve pretty much exhausted everything I know to try and get a result, but to no avail.

Comments:
-Before the total failure, the machine started well twice after the initial freeze. First time booted to Win10 then froze after a few minutes. Second time booted successfully on Mojave then froze after a few minutes. Both boots successful, I had a boot selection screen. Then no POST until this point.
– ***The ‘EFI DONE’ light did NOT come on*** (I am aware of this meaning. I will address it below).
– It seems to me that this machine may be the victim of an SPI Flash Failure from what I have been able to gather so far. I’ve never had this problem before, but I’m totally up for the challenge of solving it myself with hopefully a little help from you.
I don’t want to buy a new backplane if I don’t have to. I definitely don’t want to use a MATT chip. I’d rather program a new ROM chip and do some soldering.

What must be done:
– Flash a mxic mx25l3206e with a new ROM
– U8700 desoldering ROM chip
– Solder in new newly flashed ROM chip
– cross my fingers

General questions:
– How would I know if I just have a dead backplane that maybe beyond ROM repair?
– ***How ​​could this happen? I spent nearly 100% of my working time on the Windows 10 partition. Not bothering almost at all with settings or mods or anything I can think of that may intentionally have an effect on the system EXCEPT something I did to help Windows recognize my old XBOX USB controller. It’s the ONLY thing I can think of that was foreign to my daily work regimen.
– If, in fact, I am correct in my diagnosis and resolution of the major problem, what can I do to prevent it from happening again? Since these logic boards do not have a BIOS or similar dual-chip configuration, what could be done to prevent another catastrophic failure in the middle of the work week?
– The MXIC MX25L3206E that’s on the board now can’t be reprogrammed at this point, can it? Either removed or via a clip?

Repair Equipment Questions:
– Is there a preferred brand, variant or source for the MX25l3206e?
– Is there a correct or preferred variant of the CH341A programmer (I see different color editions and now a CH341A v1.7 with a voltage switch)?
– I am interested in the spi ic smd 8 pin so8w socket adapter or whatever they are called. Should I be?
– What is a good Mac compatible ROM programming interface program? I know some for Windows like NeoProgrammer and others but not for Mac.

Concerns:
– ***Should I worry about major data loss of related SSDs or HDDs after ROM replacement procedure?

Thank you very much to everyone who has read this far and to anyone who could help even a little. If I have omitted relevant information, please ask. I will do my best to provide.


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Steven L. Nielsen