Common misconception. The voltage is always on both sides of all coils at all times, right when you power the machine on. The thing that causes the “action” of the coil is the “temporary grounding” of the coil voltage. This is accomplished with the transistor.

If you have voltage on some coils and not others, then you have a problem. Check voltage using the positive on each coil lug and leave the neg. Lead on the cabinet’s “ground braid”. You should see the positive DC voltage at all coil lugs.

Most machines have multiple fuses for coils. Sometimes One in the head, one under the PF, etc. I suspect that could be the problem if you are only seeing volts at some coils and not others.

Replacing the transistor is a good first step there if it’s testing bad. What makes you think to replace the coil? If it didn’t have a meltdown and the plunger moves freely, the coil is probably fine. I would test the diode as suggested by cutting one side and testing it to see if it’s causing your “shorted” signal. (If you don’t want to wait to order a diode, just desolder one from the coin door credit switch.)

When you power the machine on for the first time after replacing a transistor, look to see if the coil engages and locks on immediately. If it does, immediately turn the machine off (before fuse blows) and look for something else at fault… report finding back here.

You hopefully know to do all this with the game OFF!

Make a “fuse breaker” and you will never waste another fuse again. Additionally, you need to put the “wires” back on the right side of the diode… it does not matter what lug of the coil, it matters what wire goes to THE BANDED SIDE OF THE DIODE. If you don’t know, it will match all other banded diodes on all other coils.