800xl keyboard failure

[JonnyBritish]

Well not quiet

 

I have an 800xl that starts up, I can type BYE to get the test and run carts etc with no issue. RAM and ROM test ok. WHat has happened is a number of the keys are either not registering or are mapping to the wrong key. Is there a chip on the motherboard that could be replaced?

 

I have had a power supply go bad that this was running of so something may have gone bad although the unit is running sofware etc so it appears isolated to the keyboard.

[Rybags]

You might try pulling the keyboard cable, give it a wipe with head-cleaner (iso alcohol) and replacing.

 

Next up, you could swap the two multiplexor ICs (74LS158s, should be at RHS near key connector). They're generic parts so can be replaced easily if faulty.

 

If none of that helps, I think there's a couple of threads about re pulling apart the keyboard itself and overhauling it.

[JonnyBritish]

You might try pulling the keyboard cable, give it a wipe with head-cleaner (iso alcohol) and replacing.

 

Next up, you could swap the two multiplexor ICs (74LS158s, should be at RHS near key connector). They're generic parts so can be replaced easily if faulty.

 

If none of that helps, I think there's a couple of threads about re pulling apart the keyboard itself and overhauling it.

 

I pulled the keyboard from a working 800xl and swapped it into the bad 800xl. Same problem. For example when i press the "1" key it registers as an "=" key for example.

I am reluctant to start pulling chips from the working 800xl to try in the bad 800xl in case i end up damaging one of these chips.

 

That said i do have a none working atari 800..would the chips handling the keyboard be the same?

[Rybags]

Those ICs should be universal among all A8s - the XEGs has them inside the keyboard though.

 

They're a generic off-the-shelf part that can still be bought at any decent electronics shop - replacing both would probably leave change from $5.

 

If both keyboards are playing up, then it's a fair chance one or both of the ICs are faulty, although the fault could be within your Pokey chip or somewhere else on the path from it to the keyboard connector.

Edited March 2, 2010 by Rybags

[rdhays82604]

After looking at Jerzy Sobolo's schematics, for the keyboard multiplexer ic's look for CD4051's

[tregare]

After looking at Jerzy Sobolo's schematics, for the keyboard multiplexer ic's look for CD4051's

 

and if you're having to replace them, put decent quality sockets in in their place and then put the chips in the sockets, as it will undoubtedly fail again eventually.

[atariksi]

You might try pulling the keyboard cable, give it a wipe with head-cleaner (iso alcohol) and replacing.

 

Next up, you could swap the two multiplexor ICs (74LS158s, should be at RHS near key connector). They're generic parts so can be replaced easily if faulty.

 

If none of that helps, I think there's a couple of threads about re pulling apart the keyboard itself and overhauling it.

 

I pulled the keyboard from a working 800xl and swapped it into the bad 800xl. Same problem. For example when i press the "1" key it registers as an "=" key for example.

I am reluctant to start pulling chips from the working 800xl to try in the bad 800xl in case i end up damaging one of these chips.

...

It does look like a circuit/chip problem rather than mylar or connector issue.

 

That said i do have a none working atari 800..would the chips handling the keyboard be the same?

 

It's still considered working atari 800XL technically since there are keyboard simulators that allow you to use the machine normally. And the console keys having nothing to do with 4051s or POKEY as those are handled by GTIA so you can still play games like an XEGS on the 800XL.

[hueyjones70]

I am having a keyboard issue with an 800XL.  Nothing works except the break key and the function keys.  I have swapped out the POKEY, both 4051s, and three keyboards that work on another computer.

[_The Doctor__]

check PIA, keyboard connector and motherboard traces/ sockets...

[hueyjones70]

PIA is good. I think I will have to replace keyboard cable connector.