Apple //c Keyboard Problem

[Jason <jasonb1963@yahoo.com>]

Recently, I purchased a used //c on eBay (the A2S4100 model).  The 
seller advertised that the computer was fully functional.  I just sat 
down to play with it a couple of weeks after receiving it, but it seems 
to be unusable in it's current condition.

After power on, I press ctrl-reset to get an Applesoft prompt.  Then 
whenever I press a key, it appears to work but then starts repeating 
endlessly within a second or so.  This is the case for about 90-95% of 
the keys.  The remaining 5-10% of the keys do nothing at all when they 
are pressed.  Pressing ctrl-reset does not stop the keys from repeating 
-- I have to switch the power off and back to get it to stop.

I've taken the computer apart and cleaned it out (including the 
keyboard) with compressed air (there was a fair bit of dust in there).  
I also reseated all of the socketed chips.  The problem remains.

Before I attempt to return the computer to the seller, is there 
anything else I can try to solve this problem?  It seems like it would 
be easier to perform a minor repair than send it back and wait for 
another suitable unit to show up on ebay.  OTOH, I don't want to spend 
a lot of time tracking down the problem and fixing it as I would rather 
be using the computer than trying to fix it.

--
Jason