Typing keyboard duplicate characters

[DavidB]

I've just got my 6128 CPC together with a gotek, new 5v power supply and external floppy after a few weeks, and turned it on to actually have a go of it and today it has started typing duplicate characters on the top number row.



It is only the numbers - I've previously cleaned dust off the membrane and there doesn't seem to be anything bad looking with it. I noticed the numbers flow through the letters below and it is generating them. None of the letters (on the other rows) produce any duplicates.



Does anyone know what it could be?

[DavidB]

I had one of these plugged in, unplugging it cured the issue - although "9" doesn't work, probably the membrane.

[Bryce]

It could be that the decoder chip (IC101 - 74LS145) has a bad output pin, but it could also be that the two sides of the membrane have stuck together at some point. Did you separate the two sides of the membrane, or just clean the outer surfaces?

Bryce.

[eto]

I had one of these plugged in, unplugging it cured the issue

You mean it happens when you have the gamepad attached but not when it's not attached?

The Sega megadrive gamepads do have additional logic inside that is not compatible with the CPC. 

[Bryce]

I had one of these plugged in, unplugging it cured the issue

You mean it happens when you have the gamepad attached but not when it's not attached?

The Sega megadrive gamepads do have additional logic inside that is not compatible with the CPC.

Oh, I missed that bit. Then nothing is broken. @DavidB : Stop using completely incompatible devices with your CPC, it could cause real damage if you're not careful.

Bryce.

[DavidB]

I had one of these plugged in, unplugging it cured the issue

You mean it happens when you have the gamepad attached but not when it's not attached?

The Sega megadrive gamepads do have additional logic inside that is not compatible with the CPC.

Yeah, I had one that switched between all four systems in the late 80's and it used to print characters on the screen when you moved it. My actual compatible joystick didn't work, but I cleaned the completely oxidised pins and now works fine.