Atari 800 keyboard partially working

[doctorclu]

I'm trying to build up a parts 800 to test installing the Incogneto board (rather than try it on my usual 800 first). I have the parts 800 almost completely working, just a glitch on the keyboard.

 

I have swapped my usual working keyboard on the parts 800 and the results are the same. I am getting these results when I type:

 

----4----9----(break works)

----r-----o----

----f----l----

----v---,----

(space does not work.)

 

I imagine I have a component/chip partially blown but if someone here can let me know which chip to replace, I will try that. (I used to know, been a while).

 

Video games completely work BTW. I played Blue Max on this computer in this state for weeks.

[Panther]

The keyboard input goes through the two 4051 multiplexers, so it's likely one of those.

[doctorclu]

That worked, thanks!