IIc Keyboard Encoder broken?

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IIc Keyboard Encoder broken?

Antoher day another broken IIC ;)

 

I bought a european version - It boots and gives me a "System OK" with Rom4x but i cant use the keyboard.

 

it reads the keys multiple times - like if i press "W" it prints "WWWWWWWWWWWWWWWW" ... 

I reseated all ICs and sprayed with contact cleaner. I swapped the original 255 Rom and checked all the traces around the keyboard encoder and so on...

oh and tried another keyboard...

 

any ideas? easy fix? 

 

rgds Dario

 

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Are all the keys behaving

Are all the keys behaving identically? Can you make it stop by tapping the key? I think that's often just the keyswitches.

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Yes they all behave like that

Yes they all behave like that - cant believe all switches on two keyboards behave like that

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One of two things here: The

One of two things here: The keyboard encoder itself is bad, or the cap(s) in line with the strobe and akn signals, are bad. ( They determine when a key is pressed, and released. )

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What caps are involved? I see

What caps are involved?

 

I see C45... but its a ceramic/tantal .. ive never seen one of these fail, only the electrolytic ones...

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twitch wrote:What caps are
twitch wrote:

What caps are involved?

 

I see C45... but its a ceramic/tantal .. ive never seen one of these fail, only the electrolytic ones...

 You're correct. But you also need to make sure that the connections between the cap and encoder are intact as well. A simple VOM can be used to check. Also could check the C46/R6 network that sets the encoder oscillator. You should also verify the Keybord Strobe (pin 16) and AnyKeyDown (pin 5) signals. That should tell you if the encoder is working properly. The first should pulse when a key is hit and the other should continue as long as any key is down.

 

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