This is the guide (https://github.com/SuperThunder/HP_Z420_…otBlock_Upgrade) I’m using and it suggests to use an Raspberry Pi to do the job. (In my case, I’m using an RPi3)
TLDR on the guide:
1. dump existing BIOS.
2. download the same BIOS version from HP website
3. copy some range from downloaded BIOS into the dumped BIOS. The range supposedly covers the “boot block”.
4. flash modded BIOS.
--------
some questions
1. My problem is that I’m having issues getting the RPi3 to recognize the Winbond 25Q12FV (SOIC16). I’m running this command to see if the RPi3 can recognize the chip => flashrom -p linux_spi:dev=/dev/spidev0.0,spispeed=10000.
My impression is that I’m not getting good contact with the clamp. I’m thinking of buying some 25Q12FV and maybe flashing a downloaded/unmodified copy of the latest BIOS. Would this work? or perhaps
(I have not lifted VCC from the board. I am assuming I only need that when flashing.)
—
2. In the event no.1 is not possible, am I better off desoldering the SOIC chip and try reading the contents using the clamp? or maybe using using something like this instead? 
----
3. Should I be using RPi3 or am I better off using something like a CH314a controller?
Thank you!
Edit by Fernando: Thread title customized