Genesis Model 1 - "down" on 3 button controller stays pressed?

Hi all,

I have a non-TMSS (if that's relevant) Genesis 1. Using a 6 button controller is totally fine, but when I plug in a 3 button controller (I have tried several), the up button stays pressed. I have tried multiple games to rule that out as well.

I don't see any cold/cracked solder joints on the controller port, but I don't get why the 6 button controller wouldn't experience the same issue.


Thanks!

EDIT: changed to Up button; sorry, had a brain malfunction while I was typing this

 

I assume you tryed the 3 buttion pad on other system?

 

Work in port 2?

 

The down button is not multiplexed so check for a hard short to ground on that pin. I strongly suspect the controller is the problem in this situation

 

He says he's tried several. So shouldn't be the controller.

 

I've seen this before, although in that case it was the up button. It was caused by one of the custom chips in the console going bad - the input pin had gone leaky and the leakage was enough to overcome the pullup resistor. In a 3-button pad, it goes directly to a button and hence reads as active - when you plug in a 6 button controller it goes through a multiplexer, and that can source enough current to keep the pin high.

 

I'm sorry guys, it actually is the Up button; I'm not sure why I typed Down.

I can confirm the second player works fine, and I can confirm it happens with all the 3 button controllers I have.

I also have another Model 1 Genesis, so I can confirm they work fine on the other console.

 

Well this doesn't sound good. Is there any fix for this, short of replacing that custom chip?

 

You could try adding a pullup resistor to the pin, but I just changed the chip with one from a scrap board.

 

I’ve heard of pull up resistor arrays going bad on arcade boards so I would try with a 10k resistor from pin 1 to 5v. It’s weird that other controllers work, but it shouldn’t hurt to try.

http://pinouts.ru/Game/genesiscontroller_pinout.shtml

 

If it's like trimesh said, may want to try smaller value resistors too if 10k doesn't work.

 

Pin 5 says +5VDC on this link, so that should be fine, correct?

 

It makes sense given how the 6 button controller is wired. On the 3 button controller, the up and down buttons are just switches to ground and the console relies on the pullups to hold the pin high when the button is released. In the 6 button pad, the up and down switches are multiplexed with the Z and Y buttons, and the output from the pad is the output of the multiplexer, which actively pulls the signal high.

 

I've definitely seen pull up arrays go bad. The flow for this repair wouldbe EMI >res array >asic

 

Had a similar issue with mine. Really had to get in there to find the crack in the trace. Hope this helps.

https://assemblergames.com/threads/sega-genesis-mega-drive-2-controller-port-fix.68243/

 

Okay, I can confirm that adding a 10k resistor between pin 1 and pin 5 did not make any difference.

If I should try a smaller value resistor as Bad_Ad84 said, which value should I try?