800XL Repair Question

[+Guitarman]

Here's the scenario.

 

800XL, has no keyboard response, although, the Reset, Option, Select and Start keys work. The Help key does not.

 

In keyboard test, I get response from the mentioned keys.

 

With the SALT cartridge installed, I get response from the above mentioned keys but it will also recognize the Break key.

 

Keyboard tested good in another 800XL. Another good keyboard tested in this 800XL fails.

 

This 800XL has ALL chips socketed.

 

I have tested with alternate GTIA, PIA, ANTIC and POKEY. I don't have an alternate CPU or MMU quickly available but could pull them from one of my modded 1200XL's if needed.

 

What else could be causing the above symptoms?? Could the CPU or MMU cause this?? What about the OS chip??

 

The strange thing is the break key working with the SALT cart but not in the keyboard test.

 

I am currently running looping tests with the SALT cart.

 

Any suggestions???

Edited January 29, 2008 by Guitarman

[Rybags]

The XL keyboard test doesn't work with Break.

 

Maybe try swapping the two keyboard multiplexor chips.

[+Guitarman]

The XL keyboard test doesn't work with Break.

 

Maybe try swapping the two keyboard multiplexor chips.

 

Which one is that?? Part number??

[Rybags]

They're off-the-shelf parts (LS, Logic Series) ICs.

The Atari part number is CO14336 according to my HW manual. Unsure what their LS number is.

But, there are 2 of them - they sit between POKEY and the keyboard connector.

[+Guitarman]

They're off-the-shelf parts (LS, Logic Series) ICs.

The Atari part number is CO14336 according to my HW manual. Unsure what their LS number is.

But, there are 2 of them - they sit between POKEY and the keyboard connector.

 

That was it!!! System is now up and running. Thanks!!