I had a couple of wonderful weeks with the v3.8 but it died whilst driving one day. No fuel pump prime, no comms, nothing.
I had it connected to my laptop via serial at the time and the failure appeared to coincide with my friend disconnecting the cable. I swapped in my 3.6 and drove home.
I suspected the C107 supply filter cap had failed because it had a split in it but after replacing it appears the split was just in the plastic covering. I also replaced the big diode there for good measure.
The power seems OK as I get 5v around the board and it draws 120mA on power up.
I tried the serial loopback start up for bootloader mode but it won't work with VEMSTune and a terminal shows no RX. I tested the 3.6 with the same procedure and get data RX fine with S,p,v command, etc.
So, the problem is not power or wiring. What could it be? MAX232 chip?
I should also mention that I had previously removed P259 chip. Comms or bootload is not dependent on that, right?