Strange Sega Genesis hardware issue

[DiscoDr.Bones]

Hi All,

A strange issue has developed with my Model 2 Sega Genesis. Under most circumstances, the Sega system seems to think that the "up" button on controller 1 is being perpetually pressed. However there is one very specific circumstance where it works correctly. It will work correctly if I have a 3 button controller in the first port and a 6 button controller in the second port. Only in this specific configuration will it work correctly, and these are genuine Sega controllers. If I swap the controllers or have only one controller connected or even no controller connected, perpetual "up." Any ideas? Is there any chance I am damaging anything continuing to play it since it does seem to work in that configuration?

 

--DiscoDr.Bones

[Bruce Tomlin]

Probably an input transistor in a chip got damaged due to static electricity and it's gone out of spec. The 6-button controller probably actively drives it from a multiplexer chip, just enough to get past the damage. If you've found a way you can make it work, that's great.