New to Vic 20. Keyboard not working. Need help!

alortegac

New Member
Jul 9, 2019
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I recently purchased a vic -20 to recue it from the recycling. I have cleaned it well and all appears to work fine except for the keyboard. At the beginning, it was totally unresponsive. I swapped a 6522A ic I purchased from ebay (supposedly tested) and now I get few characters but not all to work and a mysterious "I". I have checked the keyboard for continuity, cleaned it. and made sure the connector is ok. All seems ok. it is in good condition inside and out.
I am waiting to get another 6522 from the same vendor to swap the second 6522 to try with 2 different IC sets.

The following pictures are:

1) With new 6522 in Ub1, I always get an "I" in front of the cursor see pci 1 pic. When I type some letter work but I also get an "I" every time. See pci 2

2.- When I remove both 6522, I get no cursor. see pci 3

3.- When I remove the keyboard too, I get a cursor correctly without an "I", see pci 4


You assistance to my recue project will be greatly appreciated. Thanks a lot in advance.

Al
 

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May 22, 2019
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I'd suggest taking the keyboard apart and thoroughly cleaning the PCB. While you have it open, you can also check the state of the rubber pads on the plungers with a multimeter.
 

alortegac

New Member
Jul 9, 2019
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I'd suggest taking the keyboard apart and thoroughly cleaning the PCB. While you have it open, you can also check the state of the rubber pads on the plungers with a multimeter.
I did. I checked everything with multimeter. The fact the cursor appears with the “I” indicates it is a logic issue, imho

Thanks a lot for your input.
 
May 22, 2019
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I did. I checked everything with multimeter. The fact the cursor appears with the “I” indicates it is a logic issue, imho
However, with the keyboard removed, you don't get the "I". That tells me that there's a shorted trace on the keyboard that is closing the circuit on the "I" key itself or the row or column that "I" is connected to.

I'd check the keyboard connector and specifically look at pins 11 and 16, based on this diagram:



(credit: https://www.waitingforfriday.com/?p=470)

The way this works is when you press a key, it connects two pins together. The "I" key connects row 1 and column E, which are pins 11 and 16.

My guess is you'll find some continuity between 11 and 16 all of the time.
 

alortegac

New Member
Jul 9, 2019
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Thanks a lot! I will look for this issue tonight. Thanks for posting the keyboard matrix too. It is very strange the cursor appears correctly without a keyboard connected and I appears in front of the cursor and each letter with the keyboard connected.
thanks a lot!
 

alortegac

New Member
Jul 9, 2019
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Hi! YOU WERE RIGHT ON!! There was a short between the 11 and 16. The short was invisible as it was in the board itself, in a crossing point between the 2 circuit lines, in a thick and thin intersection. I very carefully fixed it. I used an exacto knife to cut off the circuit, drilled a tiny hole, and soldered a pass through micro bridge to bypass the short altogether.

The good news is the keyboard is ALMOST working. After I put it back together and fully tested it, I realized few keys still do not register well. The faulty keys do not follow any pattern , and some sometime work. My guess is the carbon tips in the plungers do not make good contact anymore (even though are clean and look in good shape) or the connector J1 is not making good contact anymore with the pins in the board due to all the manipulation, in and out. Not sure on what to do next, any suggestions? If this is the best I am going to get, sadly I think I may be able to live with it.....but hopefully there is a know solution for this issue.


thanks a lot for your help! Greatly appreciated.

Al
 
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May 22, 2019
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I'm glad to be of help.

It seems like the conductive rubber tips do wear out and eventually stop working as well. I've seen similar results with my 64's. One of them (thankfully, the one I use the least), is bad enough that the keyboard is not useful to me at all.

I've seen a couple of methods of renovating those conductive pads; Perifractic showed one method on his recent Commodore 116 restoration video, and I think I've seen something involving a paint-on conductive material. I'll try to dig up that information.

Perifractic's video:


And electric paint:

 

alortegac

New Member
Jul 9, 2019
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Hi, Just to let you know I managed to fix the keyboard. I applied cooper adhesive tape perpendicularly (180%) to each of plungers covering the tips. The tape adapts to the shape of the carbon tip and does not cause any issues with sticky keys. Since I do not plan to do heavy typing, I think this solution will last very long time. Now the keyboard works great. I "retrobrited" the case with saloon cream and it looks excellent, all yellowing is gone.
I will post a picture of the final assembly. My SD2IEC is its way too.

I have another non working VIC 20, from the same lot. This one turns on, but has garbled characters. Any leads on how to fix it will be greatly appreciated.

thanks a lot!
Al