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avatar_talrek

Keyboard or Mainboard problem

Started by talrek, 15:57, 21 October 14

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freemac

Quote from: gladders on 23:01, 21 October 15
Hey all :) so I have a CPC 464 which boots up seemingly pretty well to a small HDTV I have (although a slight image wobble which I'll leave for now)


But the keyboard isn't entirely working.


The Caps lock, c, b, n, m, /, \, plus 2 and + on the numpad won't respond. According to the technical specs, this makes sense - one of the lines on the matrix of the membrane has expired.


I've opened up the 464 and given everything a good clean and looked at the membrane. It all looks intact, so I guess a new membrane is needed.


Does anyone know where I can get one? :)


In motherboard keyboard connection, there is a sort of paper behind, pushing more the contact area, this paper does lose weight over time. Just add a paper more...

Bryce

Quote from: gladders on 23:01, 21 October 15
Hey all :) so I have a CPC 464 which boots up seemingly pretty well to a small HDTV I have (although a slight image wobble which I'll leave for now)


But the keyboard isn't entirely working.


The Caps lock, c, b, n, m, /, \, plus 2 and + on the numpad won't respond. According to the technical specs, this makes sense - one of the lines on the matrix of the membrane has expired.


I've opened up the 464 and given everything a good clean and looked at the membrane. It all looks intact, so I guess a new membrane is needed.


Does anyone know where I can get one? :)

464 Membranes are pretty robust. Check first whether it's really the membrane by bridging a wire between the non-working line (at the connector on the PCB with membrane dis-connected) to any of the contacts in the other keyboard connector. That way you can be sure where the problem actually lies. If the characters still don't appear, the problem is on the PCB (most likely the AY-3-8912).

Bryce.

gladders

Sorry Bryce I am not that technical...what do you mean by bridging a wire? :( I don't have any equipment, just a screwdriver and some pliers!

Bryce

No problem, no fancy tools or technical knowledge required. At the connector you need to take a piece of copper wire and connect it as shown in the picture below. Start at the top pin of the left connector and connect this pin to each of the contacts in the right connector one after another. Each time you touch them you should get a character on the screen (although not in all cases). Then move to the second contact of the left connector and go through all right pins again. If any of the characters you're missing (C,B,N,M etc) come up, then the mebrane really is the problem.

Bryce.




gladders

Thanks Bryce, I'll try to buy some wire from Maplins tonight and give it a go :)

VincentGR

I thought AY was controlling the keyboard on 6128 and on 464 was an intel chip  :-X
Can't remember correct.

TFM

Quote from: VincentGR on 15:12, 22 October 15
I thought AY was controlling the keyboard on 6128 and on 464 was an intel chip  :-X
Can't remember correct.


All CPCs have the same sound & keyboard chip, that way they are 100% compatible about that.  :)
TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

TFM

Quote from: Bryce on 10:32, 22 October 15
No problem, no fancy tools or technical knowledge required. At the connector you need to take a piece of copper wire and connect it as shown in the picture below. Start at the top pin of the left connector and connect this pin to each of the contacts in the right connector one after another. Each time you touch them you should get a character on the screen (although not in all cases). Then move to the second contact of the left connector and go through all right pins again. If any of the characters you're missing (C,B,N,M etc) come up, then the mebrane really is the problem.

Bryce.


I wrote an program to support this in an graphic way (see System Utilities), example here:




TFM of FutureSoft
Also visit the CPC and Plus users favorite OS: FutureOS - The Revolution on CPC6128 and 6128Plus

gladders

Quote from: Bryce on 10:32, 22 October 15
Bryce.


Hey Bryce, I haven't had the chance to test the keyboard as you suggest, but I have given the membrane a good clean and double checked everything else and it all looks fine, although I have noticed one of the connectors for the membrane's ribbons seems a very tiny bit loose on the motherboard, so I suspect it's that :(


Would you know who could repair it for me?

gladders

Actually, forget that - found a wire today and tested, and I can get those missing characters up! So it must be the membrane then?


Where do I find replacements, folks? :)

gladders

I think I have found the culprit having followed all the traces. All the faulty keys have one trace in common which gather into a single trace going into the ribbon that interfaces into the motherboard - and that trace has right at the end of the ribbon, a nasty scratch, on the black side.


How do I repair that kind of damage - silver paint as the other side, or something else?

VincentGR

I use "Silver Conductive Wire Glue Paste" to repair all kind of keyboards.
I even open a ZX+2 membrane in half to repair traces next to keys.
It works fine, it is elastic and drys almost instantly.

gladders

Quote from: VincentGR on 01:08, 26 October 15
I use "Silver Conductive Wire Glue Paste" to repair all kind of keyboards.
I even open a ZX+2 membrane in half to repair traces next to keys.
It works fine, it is elastic and drys almost instantly.


So do I apply it to either side of the membrane or just to the silver side? The damage that I see is on the 'black' side of the membrane ribbon, not the silver side...

Bryce

The black side is where the conductor is, it needs to be added there.

Bryce.

VincentGR


gladders

Thanks, sounds weird considering people are telling me to get silver conductive and I'm ignoring the silver side :p

VincentGR


Bryce

Explanation: The silver/carbon traces are black because they have oxidised. The other side still looks silver because the air can't get at it, you're looking at it through the plastic foil.

Bryce.

gladders

Ah I see!


So do I need to open up the whole thing to double check, risking tearing, or just worry about the ribbon?


Sorry for all the questions.

Bryce

Quote from: gladders on 16:12, 26 October 15
Ah I see!


So do I need to open up the whole thing to double check, risking tearing, or just worry about the ribbon?


Sorry for all the questions.

I'd just repait the crack you can see and then retest. If it works, then leave it at that.

Remember: If it's not broken, don't fix it.

Bryce.

gladders

I am glad to report that following a dab of silver conductant, another CPC 464 is back to full health :)


Thanks for your help!

Bryce

Congratulations, happy gaming.

Bryce.

VincentGR


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