Missile Command Track Ball Not Working in Either Direction

amplibax

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I'm working on a Missile Command and the trackball is not working in either direction on either of the two axis. Wondering what components on the pcb could cause this. I have a couple spare dead PCBs. Or is there is a good way to rule out anything on the opto boards in case there is a chance both failed.
 
I'm working on a Missile Command and the trackball is not working in either direction on either of the two axis. Wondering what components on the pcb could cause this. I have a couple spare dead PCBs. Or is there is a good way to rule out anything on the opto boards in case there is a chance both failed.
Sounds like a failed POKEY to me. Put it in test mode and see what comes up.
 
I just found a stash of POKEY chips I bought 20 years ago, if that's the problem and you need one. All 10 are NOS
 
I just tried to swap in two pokeys from other PCBs. Still nothing on either axis.
 
I just tried to swap in two pokeys from other PCBs. Still nothing on either axis.
After poking around this site, evidently the POKEY chips have nothing to do with controls. In a post a few years ago VectorCollector stated "If anything is faulty on the MC logic board it would be the LS157 multiplexer, LS74 flipflops or LS191 counters (and/or components near these parts)." in regards to trackball issues.
 
Have you looked at the schematics? There are a number of chips involved. Nobody will be able to diagnose this by just guessing.
Use a logic probe on D9 to see if you have activity.
You can see optos light up with the camera on your phone. That'll at least tell you if they are active.
 
After poking around this site, evidently the POKEY chips have nothing to do with controls. In a post a few years ago VectorCollector stated "If anything is faulty on the MC logic board it would be the LS157 multiplexer, LS74 flipflops or LS191 counters (and/or components near these parts)." in regards to trackball issues.

That guy doesn't know what he's talking about. :)
In this case, since both don't work, I'd start simple and double check that the trakball has +5V and a good GND connection. Then I'd probe the DIR and CLK with a logic probe, voltmeter or scope (preferred) to validate there are pulses at the trakball connector and then also at the logic board. If so, then get down and dirty with the ICs noted. Testing them first and not shotgunnin'.

As always -> YMMV
 
Thanks to our resident Twinkie, we know the MC opto board is based on the Sprint 4 design.
The base-to-emitter resistors are different values - see MC manual BOM (and schematic) for game specific values and connectivity.

MC_OptoBoard.jpg


 
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