C button as Start issue, Mega Drive

[angryswede]

Hi guys!

I was given a MD1 that had broken down after a switch mod. I was told there were problems with the controllers so I guessed it would be a 5 min reflow job. This turned out to be different as all buttons worked but the C button acts as Start. I've reflowed the controller ports and removed the mod but it's still the same.
Have anyone experienced this issue before?

[NFG]

Having a look at the schematic you can see that C and Start share the same output in the controller, so both are coming in on pin 9 on the controller port.

I don't have a megadrive to go any further, but the next thing I'd do is start from pin 9 and see where it's going. 

But having said that, I can't move logically through this problem.  It seems like a problem inside the controller, not the console.