MV1A Input Error

[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?

 

[lampje]

Witch of the inputs are you using?.
Are you using a controller or do you make use of the jamma connections.
The controller is digital and the jamma connector is analog.
What you can do to test is make a ground wire and test it directly on the on the jamma connector.
If this works you can rule out the controller chip that is responsible for this.
Also if you make use of the jamma connector you can test the connections with a meter if its shorted to ground.
If so a switch is stuck.
The digital part you can test with a logic probe or a oscilloscope, but most likely the logic chip (uln2803) in front of the controller chip is bad.

 

[lampje]

Here is a link to the schematic so you can look for the jamma connections.