Minor Tech: Robotron P2 stuck on - what do you think?

jehuie

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Minor Tech: Robotron P2 stuck on - what do you think?

So I finally got my Robotron working. The player 2 button tests as stuck on so that I can't play 2-player games. But everything else works. I unplugged the harness and it still shows that it's stuck on. I unplugged the 2 connectors from the small PCB (controller?) card and it still shows that it's stuck on.

Then I unplugged the ribbon cable that goes from that small PCB to the main game PCB and, finally, it no longer shows that the P2 button is on.

So my questions is....where should I look for the problem first? Is the ribbon cable likely bad? Or the small controller board? Or something on the main PCB?

I'm betting on the ribbon cable having a short in it. But I don't really know how to replace this sucker....and....I don't want to have to wait on a new one now because I'm tired of waiting on parts! :)

Thanks for any tips!

John
 
A friend of mine who knows quite a bit about these beasts just to me that there's a common failure on the interface board where one of the chips goes bad and causes issues like this. Not sure which chip but I think it's the 74LS257's. I'll head to Fry's to see if they have them.
 
you can try reflowing the pins on the ribbon connector (bob roberts sells a replacement), if that doesn't work i'd try finding another I/O board.
 
Personal opinion is I doubt that it's the ribbon cable, those are much more likely to make a bad connection, instead of making a shorted connection. It's probably a chip on the widget board. If you feel up to it, you can order that stuff it's pretty cheap, just a lot of soldering. If you look over the schematics and see which chips the p2 button connects to, you could narrow it way down.
 
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