I recently purchased my first pinball machine, a 1976 Williams Blue Chip in great shape (thanks Jay!). The machine is nice and everything was working fine when first purchased. The game plays well, but I have an issue which is more of an annoyance than anything, and I want to figure out what is going on. The issue I am having is that after the balls are played out, the "game over" light does not light. I checked the obvious items first - confirming that the bulb is working (which it is), and then proceeded to check for 6V AC at the lamp's base when the game is over, which is not present. So, next I checked continuity on the wires back from the "game over" relay switch (labelled as O/W and Y on the schematic), and those check out. The game is on free play without match, but since the match unit is on a leg of the circuit from the game over relay, I turned it on to check if it would engage when the game was over. The match unit did not engage, and a bit of checking with some jumper wires confirmed that I need to order a Flexstone file for the contacts on the leaf switches for that unit (which is shared on the game over relay, albeit on a separate switch). I checked the voltage path from yellow (which is the "hot" wire throughout the game) and the blue wire on that game over relay, and I have a steady 6V AC across it. I even engaged the tilt light and then energized the lamp just to confirm that it works if given power (which it does). I'm wondering what I'm missing here. The schematic looks to be fairly straightforward, involving the blue and yellow leads to the game over relay in a normally closed configuration (when the game is not being played, that is). Any ideas on next steps to troubleshoot this? Everything else on the game works great, and it would be nice to have this feature work as it should. Thank you in advance for any help you can provide!

We are blessed here in MN, so I've managed to feed my addiction to pinball without buying one! I went ahead and attached a jumper from the O/W lead on the relay directly to the blue lead on the same relay, and unfortunately, the light is still not lighting. As a further confirmation, I checked voltage between the yellow and blue leads on the relay and am seeing a steady 6V AC.

Hmm. Now this is interesting. Direct jumper from O/W to blue on the game over relay lights the bulb. I already tested continuity to the O/W wire from the backbox to the relay. What am I missing here? It must be something simple.

So work my way backwards towards the main power?

Well I think I've isolated the segment which is the problem. Now it's just a question of what the problem is. I connected the O/W out of the relay directly to the termination of O/W on the bulb, and the bulb lights. So now the only question is if there is anything in between (in terms of other relays, etc.). From my reading of the schematic, it seems to me that the wire from the backbox at the bulb and the game over relay is a straight line, so if that is the case, then I am looking at one of two things:
- Bad wire from the game over relay to the bulb
- Bad solder joint on the backbox or relay

Does your reading of the schematic reach the same conclusion, or is there some relay, etc. in between the O/W wire on the relay and the backbox lamp? Thank you for your help so far! I think I'm getting close to an answer.

Good news! Following your suggestion, I started at the Jones Plug and it turns out it was just corrosion/oxidation on the plug. After cleaning it, all works well again. Thank you for your help on this. This was a simple fix as it turns out, but it was a good exercise in troubleshooting and in learning how to read the schematics. Thank you again!