Before trying anything, I'd probably, CAREFULLY and gently re-seat the ICs -- clean the legs if they look really bad. You want to be super careful, because there are 3 custom ROMs (6530s) that cannot be replaced -- AND DON'T MIX the 6530's up. Each one is different, and must be in its own socket -- if you're not sure they are placed correctly, review the information on flippers.com, and make sure you have them in the correct sockets.

If that effort does nothing to improve the situation, then you can start troubleshooting...

Do a good visual inspection of the rats-nest of wires that are used to set the game options. These are old and brittle, and usually break and short with each other if you even look at them too hard. If you find a problem there, do your best to fix it and rewire it as needed to correct the situation.

Here's the next place to look. Disconnect the locked on coil before powering up the game again.

Basically, here are the steps you'll need to take (start with game OFF):

1. Trace the locked-on coil back to the driving transistor and associated driving PIA chip.
2. DMM check that transistor and its driving components for a dead short.
3. If no shorts are found, you can power up the MPU on the bench and logic probe the PIA line in question to see if it is stuck HIGH or LOW (I think it would be stuck LOW--but not sure, i'd compare readings with a nearby non-locked coil).
4. If it turns out that the line on the PIA is stuck, then that chip will need to be replaced.

Now, this game has 6520 PIA's and 3 custom 6530 chips--both types are used to drive the lights, switches and coils. If the 'bad' driving chip is a 6520, it can be replaced with a 6821. If the 'bad' chip is a 6530, you may be out of luck. 6530's are custom, mask-programmed chips and no longer available--unless flippers.com has any left--and each of the 6530's are not interchangeable -- ie, each of the three 6530's are 'different' from one another, and have to go in each's associated socket or the game will not work--this is explained better on flippers.com.

If you don't want to tackle any of this, then you can send the board to flippers.com for repair (contact them first for shipping instructions).

Good luck, and let us know what happens.