Re: 6526 failure modes?

From: Marko Mäkelä (
Date: 2002-02-13 22:57:50

Sam Laur wrote:
> Has anyone looked into the possible failure modes of the CIA?
> This has to be one of the most vulnerable components inside the C64
> with little (or indeed, on the older boards, none) protection,
> directly wired to connectors. Actually I have several dead C64's
> that have either or both CIAs shot, so maybe I should start the
> research myself, with those individual chips.

Years ago, I had a problem with the joystick in port 2, on several C64 
and C128 computers.  The direction "up" sometimes refuses to work. 
Sometimes the error was corrected by pressing all keys that are 
connected to the port 2 "up" line (all function keys, plus some keys 
near them) while pushing the joystick up.  Once, when this failure 
occurred to a C128, I opened the machine up and swapped the CIA.  Then, 
after successfully testing the replacement, I swapped the old CIA back, 
and it worked!

I think I still might have some of these CIAs in use.  Those incidents 
happened before I fried several CIAs by connecting a parallel cable from 
the user port to the printer port of an unearthed PC, so I'm not really 


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