Thank you for the detailed information. In other news, this morning I switched it on for the first time in two weeks, and it worked! I don't know what happened: I turned it on several times during the day, and it always worked. The voltage is rock solid at 5.071V.
DP13 on the boards I have is beside the heatsink for the 12v voltage regulator, seems to be a 1N4001 according to the Bomarc schematic.
QP2 is a MOSFET that’s some distance away. I wonder if you meant DP12? - that’s a BYD34J in the schematic.
I’m chasing the same problem as everyone else. Have replaced caps, DP3/DP4, optocoupler, and still have low voltage (4.3V)/wobbly screen