A good first step would be to replace the fuse with a circuit breaker, so that you're not blowing through boxes of fuses trying to find the problem.
Next, I'd unplug the Jones connectors; first, the one for the lightbox, then if it still blows the breaker, reinstall that connector, and unplug the one for the playfield. This will help you to isolate the area where the short is. You might have to manually trip the hold relay with certain parts disconnected, and be careful doing this as 50 volts can give you a decent sting.
Also, look to see if there are any coils which are obviously shorted.
They'll have a crispy look to them.
(Topic ID: 313632)
