I found the TPU firmware module. Thanks @Mov_AX_0xDEAD for tips.
GUID for tested ASUS boards is: 38715E0A_ECD3_4776_8AC4_7D93510A7468 #edit: (tested-board="ASUS Z170-PRO")
What and why, possibly how:
What is TPU unit?
Q1) Almost all Z*70 ASUS boards have this. The TPU module. It is supposed to enable auto-overclocking etc. More info on asus web or forums. (that to be said based on asus marketing of this chip)
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What i did?
Q2) I tried flashing bios with version suggested to enable BCLK overclocking. I did this by flashing the bios memory chip directly. Booted and short notification of "bios upgrade" showed on my screen, after that the board shutdown. I could not get it boot again, not even to light up any led on board etc.
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Why bios re-flash "back" to original version does not work?
Q3) IMPORTANT! TPU module starts even before the bios starts loading. Is is enabled in stand-by mode - even before user presses the power button. .
Without TPU working correctly (or at least partially correct) the board does not start. It has some conections to power enable and it holds the whole board in "reset" state. Also it ties to the LPC bus and chipset boot sequence. Bios reflash or rollback does not help the situation because this bios does not even start loading to PCH so it can not re-flash this chip back.
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How did i find GUID and flashed the TPU firmware back to original version?
Q4) The MX25L512E memory in this case is routed directly on board. I connected my digital analyzer and reverse-engineered the pinout on board. I read the memory and used this data to find original raw data in bios flash under mentioned GUID. Using the same GUID i found the TPU FW in old bios for this board.
De-soldered, programmed and re-soldered the memory to board. (While soldered on board the write-protect is brute-forced being tied to power-lane.)
After i flashed correct version of TPU-FW to the MX25L512E and soldered it back with old bios being in the bios-flash memory, the board STARTS NORMALY.
Conclusion:
A1) TPU FW has a lot to say in board boot and power-on sequence.
A2) Flashing wrong bios (eg. ASUS z170-pro gaming, instead of ASUS z170-pro ) can and most likely will result in bricked board.
A3) Board can be resurected from this, but it requires re/de soldering the TPU FW memory. Also, TPU-FW GUID might differ between boards production generations.
TPU-FW_ASUS-Z170-PRO_MX25L512E.zip (52.9 KB)
