Atari 800 keyboard decoding

[Wookie]

I've got 2 Atari 800's that don't properly read the keyboards. I think the problem is NOT in the keyboards, but rather in whatever circuitry or chip in the computer reads the keys. I say this because I was able to substitute a known good keyboard into both machines and the faults didn't change. One computer doesn't react to any keypresses, whereas the other consistently fails to read only some keys (6 and 7, for example). When the known good keyboard is installed, the 1st machine still doesn't react to any keys, and the 2nd still doesn't read 6 & 7 (and some others).

Any help is appreciated.

On a more general note, can somepne point me to a website that has comprehensive troubleshooting and repair info on the Atari 8-bit line? I had no luck finding anything like this thru a Google search.

[channelmaniac]

It goes through RN1-4, 2 CD4051 chips then to the POKEY. Start with the 4051s then replace the POKEY.

Check the resistor networks first. They are individual resistors in a pack and not bussed. (bussed = common leg tied to ground or +5v) Pins 1-2 is one resistor, pins 3-4 is another, etc. Look for a resistor that is much higher than the others in the pack. If you find one like that, or one that reads open (infinite ohms) then replace the pack.

Next, check the 4051s. Actually, you can swap the 4051s around to see if the problem changes before you replace the POKEY.