NES Controller Ports Not Working!

Have gotten 2 NTSC NES Front loader consoles which i planned to NESRGB mod, i have modded one successfully but have noticed that the 2nd console none of the controller ports appear to work. I could understand if 1 didnt work and could put that down to a dry solder point or broken wire but for both of them not to work seems a tad odd, i have tried the pad in the other NES console and it works fine so the pad isnt the problem.

Any ideas what could cause such an issue??....does the PPU chip in the NES have anything to do with the pad ports at all??

 

Uh no, not sure why you'd think that. The controllers are read by a couple of 74HC368 buffer chips and then the controller inputs get sent to the CPU.

 

Ah ok, just that with the NESRGB mod you remove the PPU chip from the motherboard and place it on the NESRGB pcb, was just wondering if the PPU had any control over the controller ports at all.

So any ideas on what i can try to fix this issue at all?

 

Did the pads work on that console before you modded it?

 

This is the thing i bought them before xmas, and cannot remember if i test the pad ports or not

 

Could be the region thing if you are using uk pads on a us console?

 

No, PAL controllers work fine on an NTSC console, it's actually the other way around.

 

On a NES we have a set of zener diodes on the path that go to the input buffers (mentioned by ApolloBoy) which in case of a overvoltage incident(perhaps accident ?) protects the buffer chip and the NES CPU from receiving that "zap". If it shorts out it will block the controller port from working, needing replacement or removal.

 

Hmm where are these diodes located please??.....

 

DA1 DA2 DA3 DA4 right in the middle of the picture lol

Each pair is for one of the controller ports. It's a "integrated circuit " which has the said diodes inside ... lol

 

So i can remove these completely and see if it sorts the problem and then buy replacements if needed?

 

Ok i have removed both pairs of the zener diodes input buffers and the pad still doesnt appear to work in either port. I have connected up a NES Advantage joystick and im still not getting any response but i have noticed that the turbo lights on the advantage do light up when pressing A or B, so the port is outputting some sort of power!?.

Any other suggestions on what to try?

 

NES controllers are using a serial interface which requires 3 signals to work correctly. If any of them are faulty you get no control at all. Since you get "all buttons pushed" behavior when you push "A" it's possible that the clock (synchronization) line is cut.

 

No im not getting 'all button pushed' behavior, on the nes advantage joystick when i press either A or B buttons when the turbo mode is enabled the led status light above each button lights as it should do