Finally spent a bit of time on this on Friday night and swapped the power supply . Played about 20 games before the solenoid fuse blew again (so PS ruled out).

Also have a new problem .. the last game was one of the best I've ever had .. multiball on 3rd ball, then somehow managed to keep last ball  alive long enough to get 5 x bonus and extra ball lit and achieve multiball again  (never done that before) BUT machine malfunctioned and did not start multiball countdown .. just sat there .. so missed playing multiball again and probably clocking the machine (was already at 640,000 or so )  .
While it was like this I opened the coin door and tried to add a credit (just to try and wake machine up and noticed score incremented a few thousand points when I fiddled with wiring to coin shute switches (weird))

Next step will be swap the driver board .. but I also want to have another very close look at underplayfield and coin door wiring .