TECH: Millipede Trackball wont move vertically



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I am troubleshooting a millipede pcb in a centipede cabinet with
arcadeshop converter. centipede works 100% perfectly in this cabinet.
i have gotten millipede to boot and can even start and play a game, but
you cannot move the archer up and down. since i am sure the trackball
works, i am looking at the trackball section of the pcb. which of the
chips in the section would you suspect are bad.

my first inclination is 10L, the 74LS257 that handles control panel
inputs. this chips looks like it has been replaced on my board in the
past. the repair job is not pretty but doesnt look to be shorting

could it also be 10R or 10P?

should i just order all thre from bob and work my way back?

has anyone ever had this issue before? if so what did you do to fix
it. thanks.



Archived from groups: (More info?)

If you're sure that the track-ball signals are getting to the correct pins,
I'd first look at the 4584 chips at locations 11P and 10N. These go bad
pretty often on _Centipede_ boards and it's a safe bet that they go flaky on
_Millipede_ boards as well. These 4584 chips are inverters... they
strengthen the track-ball signals before they reach the 74LS157 at 10P.


Matt J. McCullar
Arlington, TX