Midway S.A.M.I. Arcade intermittent problem repair

I've owned this 1970 Midway S.A.M.I. arcade game for about a year now.

When I first got it I went over the whole game. Cleaned the discs and wipers. Took apart the control unit. Burnished the connectors and perfectly aligned the film with the plane position disc.

Still it had an intermittent problem that would cause the hit relay not to energize.

I would fiddle with the connectors and jiggle the wires, check the continuity between the control unit disc and the plane position disc and the issue would solve itself for a couple months.

I can't say I play this game a lot. It's not a good game to have in a home environment. The plane pattern is too easy to memorize and then there's no challenge to the game. But I like to play it occasionally. Or like when I have some people over.  So when I turn on the game, it's always a gamble whether the game behaves or not.

So when I turned the game ON earlier this week... no dice. Again the multimeter and connector jiggle routine. But this time I finally stumbled upon the problem.

Can you see the problem in the picture below? BTW I slightly enhanced the problem to make it easier to find.

Maybe in this picture?

Turns out the problem the whole time was a broken bare wire jumper for the grey wire between solder lugs on the Hit Relay unit.

The intermittent nature of the problem came from the broken jumper just touching the gob of solder on the lug for the hit relay coil hence why jiggling the wire would "fix it" for awhile.

On the schematic, the problem would be in the red box to put it into perspective.

I completely replaced the bare wire jumper and now it's all good.

This is the kind of stuff you have to look for when working on old arcade games.