Quoted from meSz:
Looking for some input as to what to look for. F9 (8amp SB) fuse blowing upon powering up. I believe this fuse if for the controlled lamps (schematically challenged)?
Here is what I would do to start. F9 is indeed for your lamp matrix or controlled lamps. It is likely you have a short somewhere on your playfield.
These are the steps I would take to track it down:
1. Turn off the machine
2. Remove the two connectors for the lamp matrix (left corner of board)
3. Replace the fuse with a good one and turn the machine back on. If the fuse blows then it is an issue with the board, if it doesn't then it is on the playfield.
If the fuse blows with the connectors off then it is a board problem which is a bigger issue. If that is the case repost and we can troubleshoot that. My guess is it is on the playfield.
If it is the playfield then do this:
4. Turn off machine, do not reconnect the connectors
5. Flip up the playfield and make a visual inspection of all the lamps and sockets. Pay particular attention to the backboard of the playfield. This game has very little room at the back and if the playfield was pushed back too hard it can crush the lamp sockets (it happened to mine). Also check for any burned out sockets and broken wires/solder joints that may be touching something.
6. If you find one that looks weird check for resistance with a multimeter across the two lamp socket solder connections. Make sure to check with the right direction relative to the diode. Try it both ways (red and black/common) and see which works (give a positive Ohms) and keep that orientation for all of them. If it has zero resistance then it is likely shorted. You can do this for all the sockets and see if you can find a short.
7. If that doesn't work you can also check the resistance between the two connector leads you previously disconnected. Again making sure to get the diode direction right. On mine it was common/black lead to red wire connector and red lead to yellow wire connector. Mine read something like 20-30 M ohms on a good circuit. If it read very low or zero you have a short on that circuit. Check the connector and solder joints first as that is the most likely failure.
Hopefully that helps as a start.