Pac-Man stuck going right

Sam Zehr

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Hi guys - having some trouble with my Pac.

The joystick is stuck right - I can go left, but not up or down. In test mode I get the constant 'Pac dying' sound. This happens even with the control panel removed and out of circuit.

Reading lawnmowerman's excellent site, I tried replacing RM8. Still happens. On the board, the resistor pack measures 1000 Ohms, except at the right input, around 343 Ohms. I figured I had a bad part - removed it. Tested a new one before installing, it was 1000 Ohms, and the same thing happened post install. I also replaced R48 while I was at it.

I'm pretty clueless on the analog stuff, so I don't know if it is even valid to measure in circuit.

I checked the ins on the 74LS367 at 8E, they are all at 5V, go to 0 if you trip the switch, except the pin 6 (right joystick) which stays around 1V, and goes to 0 when closed.

Could the '367 be the culprit? Doesn't look like anything else could be, but I suck at replacing ICs, and thought I'd doublecheck before I go through with it.

Thanks,
Sam
 
Try changing C23, I have seen these caps go bad and cause stuck inputs.
Have you tried it with the control panel unhooked? The sound looping when test is on is the sound test. Perfectly normal since you have a stuck input.
Do you have a logic probe? Probe the circuit and make sure somethings not pulling it low.
If you dont have a .1uf cap, just pull one leg and see if your problem clears up.
 
Last edited:
Try changing C23, I have seen these caps go bad and cause stuck inputs.
Have you tried it with the control panel unhooked? The sound looping when test is on is the sound test. Perfectly normal since you have a stuck input.
Do you have a logic probe? Probe the circuit and make sure somethings not pulling it low.
If you dont have a .1uf cap, just pull one leg and see if your problem clears up.

Thanks for the reply!
This is an upright, and the control panel is unhooked.
I have a .1uf disc cap - is that OK?
Sam
 
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