MVS MV1A Input Issue

[MmSadda]

Hey all, I've got an MV1A that was working fine (literally used it for an hour last night) and suddenly today, it seems to think the 'down' input is always on. Tried it in multiple cabs & with multiple carts / in test menu, & got the , same result. Pressing up or left stops it from registering 'down' for a moment, but then it starts registering down again. Any thoughts on where to start?

 

[Kujako]

How is it hooked up? Odds are better that it's a wiring or button fault, but there are things that can fail on the main board (but most failures would result in it never registering rather than being permanently shorted).

 

[MmSadda]

I should've mentioned - I tried it in a couple different cabs (with a couple different carts.)

 

[nauman]

If I am not mistaken, some of the NEO-BUF chip on a MV1A are handling controller input, which previously was done by the NEO-C1 chip on other revisions.
Since you ruled out external factors like controllers / jamma cables, it is highly likely that any of the NEO-BUF got broken since they are known to break at some point.
You can verify it with a simple multimeter by finding the input pin from the controller, make sure the signal is corresponding to the state of the "down", if it changes, find the output pin and see if it is static. If it is, well, then you know the NEO-BUF is broken.

 

[Kujako]

If I am not mistaken, some of the NEO-BUF chip on a MV1A are handling controller input, which previously was done by the NEO-C1 chip on other revisions.
Since you ruled out external factors like controllers / jamma cables, it is highly likely that any of the NEO-BUF got broken since they are known to break at some point.
You can verify it with a simple multimeter by finding the input pin from the controller, make sure the signal is corresponding to the state of the "down", if it changes, find the output pin and see if it is static. If it is, well, then you know the NEO-BUF is broken.

I’d use a logic probe if you can but this would be my approach if the system were on my workbench.

 

[Rom1]

Check pin 47 for P1 Down and pin 08 for P2 Down; both on GA7 chip.