Misile Command -- only goes down

JoeB1355

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Missile Command -- only goes down

I trying to fix a Missile Command PCB.

It works for the most part. It boots, passes self test, and trackball left and right good.

but

up goes down and down goes down.

The TB is good I tested the cabinet with a known good board

I think some signal needs to be inverted for direction -- so I must have a bad chip somewhere
 
Last edited:
Check C9 or C11. I usually change both out with new 40106's if I have any trackball issues. Otherwise you'll have to grab the schematics and go down the line with a logic probe.
 
I got a bunch of 40106's dirt cheap.

No advantage, I buy all my chips in bulk when I can and came across hundreds for pennies per chip.
 
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