CZroe Posted May 9, 2017 Share Posted May 9, 2017 I bought my 800XL last year. It came complete in box and looked to be in great condition, but I somehow managed to mangle one of the pins in the cartridge slot within my first few minutes of testing (Pitfall II). As a result, I didn't know how bad my keyboard was until I desoldered and repaired the cart slot and I was well outside of the period where I had any recourse regarding the keyboard. There were several keys on the top row that didn't work (right side), several keys on the bottom row that didn't work (also the right side), several keys on the third row that didn't work (ASDFGH), and the space bar didn't work. I followed this guy's instructions to clean the mylar except I used 99.9% pure Electronics Cleaning Grade alcohol: https://youtu.be/iJHTJIx2Qgw It got the top row and spacebar working but I actually lost the Start button. There was no improvement with follow-up cleanings. I traced continuity from every internal contact to the connector and I know the mylar is intact. I've heard tell that a keyboard matrix encoder or decoder or something could be bad. How do I check that and what do I do if it is bad? If I have to buy a new keyboard, how can I prevent this from happening? If this happened while this specific unit was in storage, then shouldn't a new keyboard from Best Electronics be just as likely to do this? Quote Link to comment Share on other sites More sharing options...
Rybags Posted May 9, 2017 Share Posted May 9, 2017 External to the keyboard there's 2 x 4051 ICs that should be near the connector in slots U24, U25. These chips allow Pokey to use 6 pins to select the 8x8 matrix instead of 16. An easy way to test if one is bad - note which keys aren't working then swap the 4051s and startup again. If the bad keys change then one of the ICs is probably bad. 4051 is still a < $2 off the shelf part so no reason not to just buy a few spares if you find one's gone bad. Pokey itself might have a problem. Good idea to lift and reseat it as well as the 2 x 4051s as an early fix attempt. There's a big stock of Pokey's around, someone near to you might spare one under $15 posted. The key matrix diagram and schematics can help identifying what rows or columns might have a problem to narrow down further tracing... 800xl.zip 1 Quote Link to comment Share on other sites More sharing options...
Stormtrooper of Death Posted May 9, 2017 Share Posted May 9, 2017 I have 2 800XL and 1 130XE and all three have a non-working RESET key. could it be the keyboard matrix aswell, or something else ? Quote Link to comment Share on other sites More sharing options...
CZroe Posted May 9, 2017 Author Share Posted May 9, 2017 External to the keyboard there's 2 x 4051 ICs that should be near the connector in slots U24, U25. These chips allow Pokey to use 6 pins to select the 8x8 matrix instead of 16. An easy way to test if one is bad - note which keys aren't working then swap the 4051s and startup again. If the bad keys change then one of the ICs is probably bad. 4051 is still a < $2 off the shelf part so no reason not to just buy a few spares if you find one's gone bad. Pokey itself might have a problem. Good idea to lift and reseat it as well as the 2 x 4051s as an early fix attempt. There's a big stock of Pokey's around, someone near to you might spare one under $15 posted. The key matrix diagram and schematics can help identifying what rows or columns might have a problem to narrow down further tracing... 800xl.zip Thank you very much! Quote Link to comment Share on other sites More sharing options...
JoSch Posted May 9, 2017 Share Posted May 9, 2017 I have 2 800XL and 1 130XE and all three have a non-working RESET key. could it be the keyboard matrix aswell, or something else ? Reset as Option, Select and Start don't use the normal keyboard matrix and are separate signals. 1 Quote Link to comment Share on other sites More sharing options...
CZroe Posted May 9, 2017 Author Share Posted May 9, 2017 I have 2 800XL and 1 130XE and all three have a non-working RESET key. could it be the keyboard matrix aswell, or something else ?Reset as Option, Select and Start don't use the normal keyboard matrix and are separate signals.My 800 (original non-XL) had a bad Start key but it was the switch itself to blame. I flooded it with isopropyl and it worked great ever since. Hope this is similar. Quote Link to comment Share on other sites More sharing options...
Rybags Posted May 9, 2017 Share Posted May 9, 2017 Console keys Start, Option, Select are connected to GTIA and have their own dedicated lines on the ribbon. Reset is also has a dedicated line and is an entire circuit and feeds to various chips and points in the system. 1 Quote Link to comment Share on other sites More sharing options...
Paul Westphal Posted May 9, 2017 Share Posted May 9, 2017 Sometimes the keyboard multiplexors go out ( 4051's ) 2 Quote Link to comment Share on other sites More sharing options...
CZroe Posted May 10, 2017 Author Share Posted May 10, 2017 An easy way to test if one is bad - note which keys aren't working then swap the 4051s and startup again. If the bad keys change then one of the ICs is probably bad. Pokey itself might have a problem. Good idea to lift and reseat it as well as the 2 x 4051s as an early fix attempt. There's a big stock of Pokey's around, someone near to you might spare one under $15 posted. Thanks again! My meter was dead when I got home because I left it on again (cheap meter). I have work all day again today so there was no way I was putting this off again. I made a trip to the gas station for a 9v battery and stayed in their parking lot checking continuity on the keyboard until almost 2AM! I used the diagram to confirm continuity for the majority of keys that didn't work, showing that the issue was elsewhere. First thing after the sun was up, I reseated the POKEY, GTIA, and 4051 shift registers making sure to switch the position of the 4051s. Sure enough, the bad keys switched from pins 1, 6, and 7 to pins 9, 16, and 17. Mystery solved! All in all, I was only 2 minutes late for work (luckily, my board was socketed). Unfortunately, I still have a problem with some of the keys on the right including Start. Though they originally worked, they quit working during all this and the problem persists through two cleanings/reassemblies and reseating the GTIA. I don't get continuity off the ribbon cable but I assume that's because of the components I see in the diagram (though I don't recall seeing them on the mylar). My LED does work and at least one of the other keys (Reset, IIRC, which seems to have a resistor instead of that other unidentified component). Any advice for these? I hate to imagine that it was such a simple fix until I ruined these somehow. Quote Link to comment Share on other sites More sharing options...
CZroe Posted May 11, 2017 Author Share Posted May 11, 2017 (edited) Don't know what I did but the keys on the right are working again. A 5-pack of 4051 shift register encoders is on the way! Thanks to the sockets, this is going to be even easier than swapping the 4021s to fix a bad NES dogbone controller. Thanks, guys! Edited May 11, 2017 by CZroe Quote Link to comment Share on other sites More sharing options...
CZroe Posted May 25, 2017 Author Share Posted May 25, 2017 External to the keyboard there's 2 x 4051 ICs that should be near the connector in slots U24, U25. These chips allow Pokey to use 6 pins to select the 8x8 matrix instead of 16. An easy way to test if one is bad - note which keys aren't working then swap the 4051s and startup again. If the bad keys change then one of the ICs is probably bad. 4051 is still a < $2 off the shelf part so no reason not to just buy a few spares if you find one's gone bad. Pokey itself might have a problem. Good idea to lift and reseat it as well as the 2 x 4051s as an early fix attempt. There's a big stock of Pokey's around, someone near to you might spare one under $15 posted. The key matrix diagram and schematics can help identifying what rows or columns might have a problem to narrow down further tracing... 800xl.zip I gotta say thanks again. I got my replacements (5x for $0.99) last night and minutes later the keyboard was working 100%. Thank you! It's not the first time I've ordered shift register/encoder chips to DIY repair a device but you did save me a lot of expense. I would have ordered another keyboard before troubleshooting further... and was about to! Now, any idea what I can do about loose keycaps? Some will fall right off if I turn the keyboard upside-down and others can tilt on their post and jam. They can be "rolled"right off with seemingly no snaps holding them in, though they don't look broken or anything. Luckily I haven't lost any. 1 Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted May 25, 2017 Share Posted May 25, 2017 Now, any idea what I can do about loose keycaps? Some will fall right off if I turn the keyboard upside-down and others can tilt on their post and jam. They can be "rolled"right off with seemingly no snaps holding them in, though they don't look broken or anything. Luckily I haven't lost any. If you look closely at the plungers (the hollow plastic parts that the base stem of the keycap slides into), you'll see that all or nearly all of them will have split along the corners. Contraction of the plastics over the years seems to have made this a near-universal issue with 800's. I don't know if a definitive "fix" has ever been found but I've seen numerous suggestions: mixing some epoxy to individually repair each plunger, lining the inside of each plunger with a piece of thing heavy duty tape like Gorilla Tape maybe (at least between the two sides bracketing the cracked corner) ... If someone here hits the $275M Powerball jackpot this weekend, they ought to fund development and manufacture of a new replacement keyboard assembly. Quote Link to comment Share on other sites More sharing options...
CZroe Posted May 25, 2017 Author Share Posted May 25, 2017 If you look closely at the plungers (the hollow plastic parts that the base stem of the keycap slides into), you'll see that all or nearly all of them will have split along the corners. Contraction of the plastics over the years seems to have made this a near-universal issue with 800's. I don't know if a definitive "fix" has ever been found but I've seen numerous suggestions: mixing some epoxy to individually repair each plunger, lining the inside of each plunger with a piece of thing heavy duty tape like Gorilla Tape maybe (at least between the two sides bracketing the cracked corner) ... If someone here hits the $275M Powerball jackpot this weekend, they ought to fund development and manufacture of a new replacement keyboard assembly. LOL! I guess I can live with it. I remember that office stores once sold kits for getting custom fitted keyboard covers made regardless of your keyboard model. I believe that you sized up some kit pieces, marked down some selections, mailed it off and they would send you back the cover. The best part is that you were expected to use the keyboard with the cover in place. If such a service still exists then it seems that their cover could partially hold the keys in place or at least keep me from losing key caps when I transport it. Quote Link to comment Share on other sites More sharing options...
a8isa1 Posted May 25, 2017 Share Posted May 25, 2017 Probably not the case with your keyboard but if you pull the mylar cable out of the socket enough times the traces rub off the end of the cable. Quote Link to comment Share on other sites More sharing options...
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