ADAM keyboard issue -- membrane available?

[allansim]

Hi everyone, got out my old ADAM from storage, cleaned it up, it seemed to work ok.  Then I noticed some keys not working on the keyboard.  It was the one part I didn't clean so i opened it up, cleaned the plastics...same issue.  Looking at the traces on the membrane it seems that some keys along a given trace don't work.  V, F, E, 4, III key, +, and [

I looked the whole plastic membrane over including where it joins the controller board and don't see an issue.  Also got out my multimeter to test continuity on the non-working keypads but couldn't determine much.  My question is: does anyone make replacement keyboard membranes?  This model is 2410KB.

 

Bonus: had to laugh when I saw my full name remembered in the high score table from like 25 years ago after I played Super DK again.  Glad you guys are here!

[allansim]

Thanks for the reply.  I'm been doing some research on this, the big chip on the controller board for it is a motorola 6801.  Since I didn't see any issues with the membrane I'm going to do some continuity testing from the membrane and its connector to the pinouts on the chip to see if they are good, also the other components.  I got the schematic so that'll help, just will have to set aside some time to look at it again.  It looks like if i need to replace any component it shouldn't be too difficult to find them (other than the membrane which I could repair using your link if needed.)  Thanks again!

[allansim]

Oh no, that's a bit disappointing if there's anything wrong with it.  But given that all the keys that aren't working appear to be on the same circuit on the membrane, it's likely there isn't an issue with the 6801 and more likely an issue with contact between an input pin on the 6801 and the membrane circuit, or possibly one of the resistors on that input line (assuming its one that has a resistor, looks like a few don't) so that's more hopeful.

[phattyboombatty]

I have this same problem on one of my Adam keyboards. I haven’t had much luck with the silver conductive pens in the past. There is a YT video out there which I found helpful (I believe it was Milli’s), so maybe I’ll give it a try. 

[allansim]

On 12/1/2021 at 6:43 PM, phattyboombatty said:

I have this same problem on one of my Adam keyboards. I haven’t had much luck with the silver conductive pens in the past. There is a YT video out there which I found helpful (I believe it was Milli’s), so maybe I’ll give it a try. 

Same keys as mine or just all on the same membrane circuit?  I've been thinking about this some more and looking at the schematics, will try to open it up again this weekend.  The video i watched for taking it completely apart was:

 

Adam Keyboard Disassemble

 

So many tiny screws and rubber domes...

 

[NIAD]

Besides the schematics made available by Coleco, Archer provided this Matrix with the keyboards sold thru Radio Shack that some hobbyists used for other electronics projects.

 

[allansim]

This matrix is great help!  Looks like I should be looking at #4 lead on the cable pinout.  Sadly ran out of time on the weekend to sit down with this but this matrix should save some effort when I can get to it again.  Thank you!

[allansim]

I tested this further.  Continuity is good between slot connector 4 and the correct pin on the 6801.  Part of the track that leads to 4 on the membrane appears deteriorated and if i test low enough on it from the main ribbon lead, there's no continuity.  So i ordered a conductive trace pen and hopefully i'll be able to fix it.  Thanks, all!

[allansim]

Just a little update, the conductive ink pen did not work at all.  Testing with a multimeter showed it wasn't conductive despite the name. So if you have a similar problem, go with a car rear window defogger repair kit which I will try next.

[allansim]

Last update.  Happy ending!  I tried the conductive pen again and I got it to work -- all the keys work correctly.  During application though, the 'ink' bleeds out everwhere onto the plastic membrane and the conductive solution plus its solvent gets absorbed into any tape which you may have put down to protect the other tracks/spaces, and it also ends up under the tape too.  I tried with a very small thin paint brush as well as the pen tip but it made no difference.

 

So 2 things: just apply the ink as best you can, remove any tape you used, then clean the excess ink solution away with a fine edge, like an exacto knife blade.  Once its more or less a new track with no more bled out solution touching the other tracks that you can see, you have to let it dry for a very long time, like 8 hours or more before trying it or testing with a multimeter.  If you do get cross-conduction then it should still be possible to scrape away any excess dried ink bridging the tracks using the exacto blade.  That area of my keyboard membrane looks like a mess now but at least it conducts the signal properly and will be good enough until when/if membrane reproductions are made like those smug ZX Spectrum and Atari computer users get to enjoy.  I have a 500XJ Epyx joystick with a similar issue I may try to fix another time in a similar way but I expect that to be even more difficult.