Snes motherboard problem

[Pikkon]

Well I have a strange problem with this snes Im trying to fix,everything works great except the b button does not work when playing a game,the controller ports are fine as I tested them out with my own snes and everything works properly.

I thought maybe the ribbon cable might be damaged so I solderd 11 wires from the controller ports to the motherboard and still the b button gets no response,you guys know what's going on?

Edit

Just did some more testing and controller port two works great but the problem still persist on controller port one.

[Nemesis]

I'm not a SNES hardware guru, but if you've got a multimeter that can test resistance, I'd power the system off, and test right from the pin on the controller port back to the point where the trace connects to whatever controller chip handles IO. If the signal doesn't get through, trace back at key points until you identify where the break is. If there's no sign of a break, well, you've got a larger problem.

[Pikkon]

Well I used a multimeter and I can't find a short anywhere,this is one bizarre snes.

[Bad_Ad84]

Pretty sure all the data from the controller comes over the same couple of pins. You wouldnt just have 1 button not working if it was that.

I assume its an issue with that signal being decoded back into separate button presses. Where ever that is happening is probably where the problem is

[vince4321]

Can you remove the controller ports from the mainboard (unplug ribbon cable) and try another controller port from another snes. Then you will know if the problem is with the controller ports or with the cpu/mainboard. The way the snes detects whether the b button is pressed is different to how it detects all other button presses. The SNES controllers drive data for the b button at the falling edge of latch. Data for all other buttons is driven at the rising edge of clock. A logic high on the serial data line means the button was not pressed, somehow the b button is not sending a logic low signal when it being pressed, or the cpu is not looking for it.

[Pikkon]

I did exactly that when I first noticed the problem.

But its weird,I tried a nice chuck of my games and when I played super star wars the b button worked but ever other game got no response.

[bart_simpson]

Could be dirt on the ribbon connecter.?

[l_oliveira]

Actually the SNES and Super Famicom have a set of protection Zener diodes on the inputs (the P and N 3 pin parts that are close to the controller port connector on the mother board).

Have that verified.