Williams IJ Switch Problem

eb94110

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I am having a very frustrating problem with the switches on my Williams Indiana Jones. The switches in Row 5, specifically, are not working. I noticed it at first because the center drop shot did not result in the "Ball 1 Locked" message display. Then, that message would randomly come on during game play even if no pinball was shot down the center drop.

Now, none of the switches in that row (#5 per the schematics) are working consistently. Some will occasionally work, but when they are triggered in the switch test mode they are identified as incorrect switches, for example, #55 is displayed as #85, or another switch on the mini playfield is triggered and the DMD identifies it as the switch for "Trough 2." Also, if you push the top right and left mini p.f. switches at the same time, they work, but they do not work individually.

The mini playfield was disconnected completely to see if that would make a difference, and that made no difference. The wiring seems fine. Seems like something is shorting, though. Any thoughts?

Thanks for your time.
 
Check your CPU board. Look at the batteries and see if they have leaked. If you get battery leakage it will mess up the switch matrix.
 
I'm not sure if you can test the chip, but the one you'll need to look for is the U20 chip on the CPU board which is a 2803A chip. On an IJ it's probably soldered in so it will be a pain to get it out. Hopefully your U20 chip is socketed in.
 
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