I had some very thready boot issues with my Blackout until I replaced the .156" male headers on the MPU and solenoid board. Also got them from Great Plains Electronics.
If not done so already, build up the power supply per the Vid1900 instructions (caps, diodes, resistor, voltage regulator replacements), and look carefully at the bridge rectifiers for burn marks, I replaced those as well. They were cheap and the new ones run much cooler.
Keep a close eye on what could get shorted out when the playfield is lowered; I had a few diodes and switches that got bent about over the years that would short out on playfield drop. I replaced most of the diodes that were questionable with 1N4004s on solenoids and switches.
Needless to say, it was a lot of work but the basket case I got is now working 100%.