c64 keyboard that's really a Vic 20 keyboard problem

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Avro707A
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c64 keyboard that's really a Vic 20 keyboard problem

Post by Avro707A »

Hello, I have a keyboard in which the following keys don't work, no matter the pressure (here is the staggered order so there seems to be a pattern, maybe)

___YU
_GH
VB

I took the keyboard apart but it didn't look like any of the c64 keyboards on you tube videos and sure enough, printed on the keyboard was vic 20. It has the rubber "cups". Anyway, found a good video on line, cleaned the contacts and the "cups" but still ave the same problems. Has anyone seen anything like this? The wires still seem soldered strongly unless the problem is in the connector to the c64's pcb. Thank you for any insights or ideas you have. I'm not a technical genius by any means but it'd be nice to save this keyboard.

Chris


banman
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Re: c64 keyboard that's really a Vic 20 keyboard problem

Post by banman »

Hi Avro707A,


I have KU style main board C 64 that's got a VIC 20 branded PCB keyboard too. I can confirm that it is original and came from the factory with this.

I think Commodore used whatever they had on hand at the assembly plants.

I would do a quick continuity test on the wiring harness and PCB to confirm that it's well and good.

Commodore VIC 20 and C64 keyboards are the same and use a matrix system so maybe a group of keys may become inoperable if there's anything wrong with one trace on the keyboard PCB. Even the tinyiest of breaks like corrosion can cause continuity issues. I've experienced that before. It wasn't visiable with the naked eye.

Here is a few diagrams of the C64 keyboard matrix. You could confirm the non functioning keys that lay along a predefined electrical path by studying these diagrams.



https://www.google.com/search?q=commodo ... e&ie=UTF-8



Check out Sven's website....

http://tech.guitarsite.de/conductive_rubber.html

He has got a very interesting way to rejuvenate the conductive carbon rubber parts.


Ray Charlsen has a very good article on keyboards too.....


https://cbm8bit.com/articles/ray-charlsen/article7

Hopefully you haven't got a broken VIA chip.


You also might swap the 2 VIA chips on the C64 mainboard around if they're socketed and observe if there are any changes to keyboard operation.

I hope this helps.....
levoman
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Re: c64 keyboard that's really a Vic 20 keyboard problem

Post by levoman »

The vic20 and C64 keyboards are exactly the same pinout .
I know this from my keyboard project on here!

viewtopic.php?t=15160
Avro707A
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Re: c64 keyboard that's really a Vic 20 keyboard problem

Post by Avro707A »

Hi banman and levoman, thank you both very much for your replies and guidance. Banman, the c64 keyboard matrix was incredibly helpful! Using that matrix I continuity tested known good keys (needle moved) and then the problem keys and sure enough with that grouping of keys the needle didn't move so it must be that trace I guess. The wires and connections from the pcb to the socket/plug look solid so I'm thinking it must be the pcb. I do have another keyboard and it works perfectly so the VIA chips must be alright, but batman, that was a genius idea to test if it had come to that. It must be like you said, something not readily visible.

Levoman, that's a pretty amazing project you've got going on there... ps2, now that is creative!

You both are too smart for me and I appreciate you taking the time to reply. I may try and find a vic20 pcb if it's cheap like the one I have. It's nothing that's holding me up from using my c64 but it always lingers in the back of my mind as an annoying problem to solve ;)

Best regards,

Chris
banman
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Re: c64 keyboard that's really a Vic 20 keyboard problem

Post by banman »

Hi Levoman and Avro707A,
levoman wrote: Sun Feb 06, 2022 11:32 am The vic20 and C64 keyboards are exactly the same pinout .
I know this from my keyboard project on here!

viewtopic.php?t=15160
Good point! ;)

You could always build one of Levoman's excellent keyboard adapters and connect it up to a IBM PS2 style keyboard. You would then be able to positively identify if the issue was coming from the keyboard or the C64 mainboard.

They are easy to build and cheap. Great for the toolbox. Most of the parts can be got off eBay or Aliexpress.
Levoman has found a source of OEM crosspoint IC's if you're that way inclined.

Here's the link to Levman's Keyboard adapter build.

https://www.levosretrocomputerprojects. ... rd-adapter


One important note to keep in mind with this project is that this current adapter will only accept PS2 keyboard type protocols, newer USB keyboards use a different protocol.

Now, having said this I have tested a few USB keyboards and they all work fine. I suspect that the keyboards I have reviewed utilize the PS2 type protocols. Your mileage may vary.

I believe PS2 style Keyboards and mice are big in the PC gaming community.

I picked up a very nice retro 'in box' PS2 Compaq keyboard from eBay recently for $20AUD. So there is stuff out there still.

You may have an old PC keyboard laying around the house.

I am not sure if you are a casual C64 user of want to go down the rabbit's hole. A hobby like this can take you to new places. I do recommend this keyboard adapter project as something a beginner an easily handle.
banman
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Re: c64 keyboard that's really a Vic 20 keyboard problem

Post by banman »

Hi Avro707A,


No worries, I'm glad to have helped in a small way. Apologies for the disjointed reply. I think I was sending you a post as you were replying to a previous post. I take forever to type something. :oops:

I actually am not all that bright, but thank you very much for the compliment. :D


I have a question for you. I am an inveterate inspector, I can't help myself.
What is the revision Number of the C64 main board you have? It will be lower right side of the C64 mainboard. Take a pictures if that's easier. It might be a KU-14194HB style revision.

https://www.c64-wiki.com/wiki/Motherboard


Have a look at this thread to see how small the break can get on a PCB for it to cause an issue. It was absolutely tiny, the pictures are magnified heaps. I could not see it all with my naked eyes.

viewtopic.php?t=12931&start=40



I only added the smallest amount of a solder ball to the corroded area and the problem was fixed. Not my finest hour but it did the trick.

I think from memory it was a section of the PCB that had a small copper dot test pad. The trace leading to it and away from it had the smallest of breaks. This caused the same matrix discontinuity issues you are experiencing on your keyboard.
I only discovered it by accident when I pressed multiple keys at the same time on the remote control the button that was not working would come back to life again.

I am positive if you look and track back very carefully you will find the broken trace.

I used a free app on my aging smartphone called 'Cozy magnifier and microscope'. It can use the phone's flash as an additional light source. It is without a doubt not the best app tool out there, however it suits my simple needs.I am sure there are plenty of similar magnifying tools out there either for Android or IOS.
I suggest you pick something you feel comfortable with. Or a plain old magnifying glass might do.
This app tool helps me to look closely at the traces from all angles to see if there is anything unusual that requires further investigation and testing.

Rule out the areas that have good continuity. So for example check the keyboard connector socket to the keyboard PCB and make sure it is good. Use your meter and eyes as well as a magnifying tool together.
Then check the keyboard socket to a bare metal contact point close to where the connector wires attach to the PCB to rule that section out. Try not to damage the green paint on the PCB (that's solder mask and is used to help prevent solder bridges in manufacture and also importantly corrosion of the copper tracks in the life of the part).
Keep working your way around the PCB until you think you can identify a section that might be a likely cause of problems. Use your eyes, meter and any magnifying tools you have. Look all around the area, move the part in your hands in good lighting to attempt to expose a problem. If it is corrosion it will be the very smallest of breaks, probably not even visible to the naked eye. Use your meter and magnifying tools here.
Corrosion can occur under the green paint (solder mask). Though it will most likely attack the bare exposed copper parts that don't have this green paint first. Remember the remote control repair I referred to earlier in this post? I actually pulled the SMD IC off before discovering the small break due to corrosion on the PCB. That was a complete was of time for me. It was like the copper trace wasn't layered down on the PCB around the copper test dot during manufacture. However it must have been, the neighbour said it worked at some earlier time.

If you do find the break, great!

You can do several things to fix it up. If it's small, just a dube of solder will do (like I did on the remote control). If it's bigger you might consider laying down a jumper wire. One could do a jumper wire from a near by solder joint to a another solder joint spanning across the known break on the PCB trace. It will look a little ugly, however the repair will not ater the PCB so the repair can be reversed easily at a later stage if a 'better you' can do a tidier job.
Alternatively, one could cut in a very small strand of copper wire at the break. To finish the job a small amount of laquer to cover the repair and to protect against further corrosion. This of course will do some damage to the pcb. This of course might not be what one wants to do.


I hope this helps. Let us know how you go at finding the issue.

Send us some pictures please. :D
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