Recover Dell Precision T7600 by flashing it's BIOS on working T5600 by swapping chip

[aletib]

Hi ladies&gents and thanks already because I learnt a lot reading tons of posts: I used to play with that stuff ages ago when things were much more simple and I am surprised to see how complicated it has become!

Now, let me try to summarize what my situation is (I hope I didn't forget key elements, if so, let me know).

target: Flash T7600 Bios from a T5600

HW: I have 2 engineering (preprod) Dell Precision Systems: T5600 (up&running), T7600
what happened: T7600 doesn't finish post after playing with intel AMT settings. CMOS reset through MB didn't work. Probably the only way to fix it is to flash the BIOS because AMT parameters are not stored together with CMOS.
to know: both motherboards use the same EPROM chip which is hosted in a special socket: when opened it cuts electrical contacts so it is safe to replace the chip while the machine is running.

What I tried until now (I boot the T5600 with it's own BIOS then remove the EPROM and replace with the one to program; all DOS tests ran under Hiren's boot CD from a YUMI-created USB key): 

1) Dell BIOS flash update; with this I am able to flash both chips from the T5600 with its own BIOS. Obviously if I try to use the T7600's download BIOS, the software doesn't run the update. I tried with /s /force and even if I don't receive the "wrong bios" error, the utility exits back to DOS without doing the update.

2) Extracted the BIOS from dell archive with phoenix tools 2.66 so I have a bios.gpz and a T7600A12 file but I am unable to flash them; tried with phlash tool under dos: it checks the file and then tell me "signature not found in the interface" and exits. Pubkey (x1) Marker (2.1) (Dell CBX3) (x1) status: "EFI / Insyde BIOS (Dell HDR)"

3) InsydeFlash doesn't run (Win10x64) telling me it cannot load a driver and to run it as administrator (which of course I do).

4) tried CTRL+ESC while powering on (should bring up a recovery interface/poll the usb key): doesn't work

So chances are:
- I am passing the wrong file to the phoenix flash utility because I didn't understand/found documentation on what the whole signature/SLIC/etc is (if I got it right it's a signature system that prevents people from modifying the BIOS).
- I am using the wrong method/software/parameters in order to force the BIOS flash.
- I didn't correctly extract the BIOS form Dell's .exe package (it's one that doesn't support command-line parameters to do so, don't know if precision system have a different kind of BIOS or simply more recent but the write/extract ROM and hdr to file parameters do not work)

Any help/advice would be greatly appreciated.

PS: If you want to suggest and test, please don't forget not to include in the command line parameters that affect the machine's CMOS/NVRAM parameters because I'm flashing a chip for another target machine while the one I'm running the flash utility on is working well and I'd like to keep it this way

thanks a lot!
Alex

[aletib]

some updates:

1) I said that /s /f didn't work: false. what happend is that the utility gets the system ready for flashing but that won't happen until the system is restarted
2) the swap-good-chip--after-boot-with-failed-one technique doesn't work: when the machine is restarted the flashing won't start beause the machine can't restart without a proper BIOS.

Beside Dell's official utility I haven't been able to use any other tool to flash the BIOS: I bought a CH431a programmer on ebay and a couple of spare chips in order to play with them without compromosing the working T5600.

[aletib]

some updates:

1) I said that /s /f didn't work: false. what happened is that the utility gets the system ready for flashing but that won't happen until the system is restarted
2) the swap-good-chip--after-boot-with-failed-one technique doesn't work: when the machine is restarted the flashing won't start beause the machine can't restart without a proper BIOS.

Beside Dell's official utility I haven't been able to use any other tool to flash the BIOS: I bought a CH431a programmer on ebay and a couple of spare chips in order to play with them without compromosing the working T5600.

Another update: I ordered a new motherboard in order to be able to get a snapshot of the roms and just discovered that the engineering pre-prod model I had, used 8+2MB eproms while the production motherboard I received has 8+4MB which could explain why the Dell updated wouldn't flash the BIOS. I have now ordered 4MB eproms in order to write the BIOS I grabbed from the production motherboard. Cross fingers for me as I have no more ideas on how I can fix it without being hable to hack the ROMs content myself.

I'm quite surprised no one answered until now: did I choose the wrong forum to post in?