mattsoft Posted April 8 Share Posted April 8 So I've got this 800 and some of the keys do not work. I've tested the keyboard on another 800 and all keys test good. I've tested another keyboard on this 800 and same problem -- the keyboard has been ruled out. I've swapped the CPU and ROM boards with a known good 800 and that doesn't change behavior. CPU and ROM boards ruled out. Swapped out memory board without luck. Memory ruled out. I've swapped the POKEY and nothing. POKEY ruled out. I've check for obvious broken solder joins on the keyboard pin header, and reflowed the pins without luck. Are there any other ICs (like logic chips) that are known to be troublesome on the 800? Most of the keys works, but BREAK and ENTER (and maybe a couple others) do not. Weird! Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted April 8 Share Posted April 8 (edited) check the keyboard connector itself, the contact swipes in its' slot, and the leads going into the board are not snapped or broken, the support chips next provided no components look damaged, cracked or burnt as well as solder looking nice with no flecks laying about shorting things Edited April 8 by _The Doctor__ Quote Link to comment Share on other sites More sharing options...
Beeblebrox Posted April 8 Share Posted April 8 (edited) @mattsoftAs the doctor says, check the keyboard support chips next for socket damage, etc. These are the 2 x 4051 chips to the right of the pia (6520) chip. Replacing them is cheap and easy as they are still readily available to buy from any IC supplier, as well as eBay, but make sure you are happy with the sockets and vias, traces on the board. The 800 build quality is excellent, but these are over 40 years old. Socket and chip leg oxidation can impede contact. You can reseat chips like the 4051s but pressing down initially, lifting them slightly with an appropriate IC tool, them press down on them again. Edited April 8 by Beeblebrox Quote Link to comment Share on other sites More sharing options...
mattsoft Posted April 8 Author Share Posted April 8 Thanks all. I will double check all of those. Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted April 8 Share Posted April 8 pin headers that have varied brownish varnish looking coloration need a cleaning Quote Link to comment Share on other sites More sharing options...
mattsoft Posted April 9 Author Share Posted April 9 Bingo! It was a bad MC14051B in the 2nd socket (farthest from the PIA). When replaced, all keys work. Thanks for the help all! 7 Quote Link to comment Share on other sites More sharing options...
Beeblebrox Posted April 9 Share Posted April 9 Seen this one a lot. Great that it's such an easy fix, (4051 chips are cheap and all 800's are socketed). Well done. Quote Link to comment Share on other sites More sharing options...
Like us on Facebook
Follow us on Twitter
AtariAge on Instagram
Watch us on YouTube
Chat on Discord
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.