Start by checking coil resistance looking for shorted coils -- particularly if any of them look toasty.

Yes 24v runs all coils except the relay bank reset which is line voltage. The schematic is on ipdb.org.

You can unplug the bridge rectifier (when powered off) to isolate the sling and pop bumpers. Be sure to isolate wires when powering on (I tape them)

On OXO (and many EM's), the GI does not automatically come on when you switch on the power.
You have to tap the left flipper button to activate the GI.

Read up in pinwiki or pay someone to come out and repair it. Ask them to train you if possible.

The bridge rectifier is the small black plastic square unit with four wires attached to it. It is mounted under the playfield and it converts the 24 volt alternating current (AC) supply from the transformer to direct current (DC). The coils that drive pop bumpers, kickers, and flippers are stronger and punchier when run on DC. Many 1970s Williams and Bally games had a DC bridge rectifier to drive their pop bumpers (and sometimes kickers and flippers) which would make their games play faster at a time when games typically had AC coils.

Sometimes one of the diodes in the rectifier fails, causing a direct short. This would - in theory - blow your 24 VAC fuse, however the rectifier almost always has its own fuse, mounted near the rectifier on the underside of the PF. Unless your rectifier fuse had been replaced with a very large fuse or a bad fuse wrapped in foil or something like that, it's way more likely that only the rectifier fuse would blow (not the 24 VAC fuse) if the short was in the rectifier.

Since your bonus unit was sparking, it probably wouldn't hurt to look for a short circuit there. It may be that the gear wheel that drives the wipers for the bonus unit has been driven beyond its normal operating range, this can sometimes push switch stacks into weird positions and that could create a short, or something along those lines.

That said, shorts on the 24 VAC line are nearly always due to a fried coil, which is usually the source of that burned odor inside the game. Williams games are fairly notorious for having this problem because they often have playfield switches that get stuck on, which is a very common cause of fried coils. Usually one of the score unit coils and/or a chime coil has fried, causing the short. These are easy to overlook when hunting for a bad coil. The good news is, you can nearly always find a fried coil with just a visual inspection because it will LOOK fried - it will be black and parts of the plastic housing may be melted.

A common technique to narrow down the location of the fried coil is to turn off the game, unplug all playfield cables from the game, and then power the game back up. If the bad coil is somewhere on the PF, then the fuse won't blow any more. If the fuse still blows with the PF unplugged, then the bad coil is in the bottom board or the head insert.

Sometimes the cause of the short is something other than a fried coil, but the odds are good that is what you are dealing with, so it's worth your time to make 100% sure all your coils are good before looking elsewhere for the problem.

- TimMe