Mon Apr 12, 2021 7:58 pm
Swapping flash chip would probably work, there is no encryption or other check that would pair specific CPU with specific flash memory. I haven't done flash swap on 750g3, only on older rb4xx boards and they were OK after the surgery...
But maybe first start with measuring the voltages on electrolytic caps. Usually switching regulator is what fails, if that's the case, you can power the board using bench PSU, by manually supplying the required voltages. It's good to measure the voltages on working board first, then solder wires to old board and supply it with same voltages (should be 3.3V and maybe 1.8V). Some boards create lower voltages from 3.3V so in that case all you have to supply is 3.3V and board will boot up. I repaired one of the original 750 (not g3) boards that failed just like this by just replacing failed PSU circuitry by a cheap DC-DC module and it's still running some 5 years later...
Only real bad scenario is when input switching FET in regulator fails shorted, in that case full input voltage gets into CPU and other chips and everything will be dead. If CPU or board starts to heat up a lot after you supply your voltages from external PSU, it usually means chips are destroyed and shorted inside thanks to overvoltage. (It's good to set some current limit on your PSU to watch for this). In that case the flash memory is likely dead too... and there is no point replacing it an to another board.