Trying to fix a faulty Genesis/Mega Drive controller port

[Ampera]

This has been an issue for a while.

I have a Sega Mega Drive/Genesis. It's a model 2 system.

The issue is that the second controller always has right pressed even when it's unplugged. I am not a complete rock with electronics so I tried some obvious stuff. I made sure nothing was bridged on the board, and I looked in the port's pins and didn't find any bent pins. The RF Shield makes no contact with any of those pins either. I tried looking at stuff with a multi-meter, to see what pins were connected. It was really confusing and several pins were actually connected, but this was identical on both controller ports.

I have looked and looked into the system again, but I don't really have that many things to test stuff with and my knowledge of Mega Drive internals with me knowing it has a few commonly used chips.

If anyone has any suggestions of what I can try it would be a great help.

[Mephitus]

Likely there is a short on the controller port pin 4 and 5 inside the system. If you have a multimeter with a continuity check, you can check for the short.

Side note edit:
While you are inside the system, I HIGHLY recommend a full cap replacement. I have serviced 5 or 6 units before and have never run across a "good" cap in any of them. If you are interested, there are also a few minor mods I can recommend for improved video output.

[Ampera]

There is a connection on pins 4 and 5 on the first port but not on the second. Maybe it's supposed to connect and it doesn't? I am not sure. It is the second controller port, and it does that even without a controller in.

[Mephitus]

I have a gen2 genesis in storage. I am at work right now, but when I get home, I will pull it out and see if I can figure out how it's set up on a known functional unit.

[Rasz]

I have bad news for you

bad: megadrive esd protection is inside the chipset, if its blown its game over.
maybe good: you said pins 4 and 5 are shorted one one of the ports, most likely you confused ports around and its the bad one shorted, if you are lucky short is in the connector

pad pins go to ferrite inductors for EMI filtering, and then straight to the chipset, there is no other place they could be shorted
you can desolder inductors to check where the short is (easier than big joypad connector)

[Ampera]

No P1 has 4 and 5 show a number on my DMM's beeping function thing (The proper technical term, eh?) I looked at the pins, the bridges, everything no visible shorts like solder bridges.

[Rasz]

No ... beeping function thing ... no visible shorts

ok then

[Ampera]

Yea my technical terminology is not the best. Especially with DMM's since I just learned what DMM meant yesterday.

[Ampera]

Any other suggestions?

[Rasz]

Any other suggestions?

you can desolder inductors to check where the short is (easier than big joypad connector)

[Ampera]

I am not sure what you mean. I desolder them and then what?

[Rasz]

I am not sure what you mean. I desolder them and then what?

hmmm, look for a good electronics repairman in your city

look for a hackerspace/makerspace, someone will be happy to help you in person

[Ampera]

No I want to do this myself. Sorry if I seem arrogant, but I don't want to spend money that I honestly don't have on someone to help me. All I have to my disposal is soldering equipment, a DMM, and the genesis. I can get replacement parts though.

All I want to know is what you mean?

[Rasz]

in hackerspace people will help you for free
I told you what to do, but your answer was "I dont see no shorts" 

[AmmoJammo]

http://emu-docs.org/Genesis/mega1.png

check pin 60 on IC6, could be a solder ball bridging from in to the pins next to it.

If that checks out ok, the IC is most likely toast.

Edit:
Actually, I think thats the wrong schematic 

[AmmoJammo]

Pull EM24 which is the filter on the "right" signal of the player2 controller port.

They are a 3 pin device, which makes me think they're an inductor/capacitor in one, with the centre pin going to ground.

[Ampera]

Yea, I think it is. From my guesses that is a model 1 schematic. I have the compacted redesigned model.

[Ampera]

Thanks for all your help, but unfortunately it's no longer needed. I tried to test the system to see how the controller was effected, and it did not turn on. I have given up and decided to just buy a new Mega Drive.


Rest in Peace, Bob the Mega Drive.

There will be a funeral and a parade in his honor. He will be buried with all the famous war veterans, and have a large tombstone in his honer.

*Salute*