OK, here's my standard disclaimer: I'm willing to try to troubleshoot electrical issues, but I'm learning as I go and haven't learned much yet. So, please be gentle.
Just got a HH that was not working. F4 solenoid fuse was blown. Replaced and blows immediately upon power up (as in instantly). System 80 pin wiki said first step was to check bridge rectifiers. 2 of 4 tested as bad. Replaced all 4 and the orange cap. Still blowing F4 immediately. Things did light up more brightly including the displays though... so, thinking that's progress. By the way, I can start get the display to show a new zero score one player game, but there are no sounds and no coils fire.
I noticed that the diode at CR7 on the power board was looking sketchy. Disintegrated when I tried to unsolder it. Have a replacement on order (found different recommendation for that and corresponding resistor on a separate thread).
Also was reading beerorkid System 80 troubleshooting which recommended starting by testing all coil resistance and make sure none test below 2. One of the 4 main playfield flippers tested at 1.8 versus 2.4 for the other 3. Pulled wires from one lug and retested and got a much higher figure (30+ as I recall). Site says " If the resistance is higher than 2 ohms [after removing the wires for one lug], the coil is good but the solenoid driver board transistor is shorted and will need to be replaced." I've ordered some transistors and will try to track down which one is associated with that flipper and do the replacement.
So, my questions are:
is the bad transistor (or even the CR7 diode) the likely cause of the blown F4 fuse? Or should I still be looking for something else.
Does the CR7 diode explain why I'm not hearing any sounds when pressing the start button?
Thanks for any advice.