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avatar_ervin

6128 keyboard woes *** SOLVED ***

Started by ervin, 07:24, 07 April 12

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ervin

Hi all.

Recently I got myself a 6128 - a dream come true after all these years!

However, there were a few things wrong with it, like a dodgy disk drive and some dead keys.

Well, the drive was easy enough to sort out thanks to a new drive belt, but the keys are a different matter.
I've been doing a lot of research, and Gryzor and 00WReX (cheers guys!) have been providing a lot of advice and suggestions, but so far we are out of luck.

The following keys are dead:
DEL SPACE Z X V , .
and on the numeric keypad 0 and .

Of course most of you will recognise these as being on the same line on the keyboard membrane.

Now, I've gone over the membrane lines with a microscope, under a bright light, and I can't find any breaks or fractures.
I've cleaned the keyboard contacts both on the motherboard keyboard connectors and on the keyboard ribbon.
I've removed all the dust and grime I could find.

But nothing has helped. The same set of keys are still dead.  :'(
I've even pressed the contacts on the membrane directly while the cpc was on, and that same set of keys were the only ones that didn't work.

Does anyone have any suggestions?
Is there some way of checking where the break is using a multimeter (is that what it's called?) or something like that?

I learned from 00WReX that both the AY chip and joystick logic passes through the keyboard connector circuits, and those all work fine, so the connectors on the motherboard must be ok.

Could there be a fracture in the ribbon in the bit that plugs into the motherboard?
(ie. the part of the line hidden behind the thin bit of plastic)

Could I (should I???) perhaps trim the ribbon and check if the newly exposed lines will work?
:o

Thanks for any help.

00WReX

#1
Definately good to get others input...but just to clarify, I mentioned that the keyboard connector circuits go off from the connector into both the AY sound chip as well as the 74LS145 decoder chip.

You mentioned that you get no "X" from the keyboard but the Joystick fire button produces an "X". So my thought is that hopefully this indicates that the AY chip & decoder chip are actually OK.

But the actual keyboard ribbon cable connector socket on the motherboard could still be the issue...even a dry solder joint, etc.

Just for reference, attached is the keyboard switch matrix and the keyboard connector component of the schematic diagram.

Ervin's 6128 has lost all the keys off connector no.10 in the switch matrix...

Cheers,
Shane
The CPC in Australia...
Awa - CPCWiki

protek

Don't know if this is of any help but I had a fracture in my Spectrum +3's keyboard ribbon, rendering some of the keys inoperative. I simply applied some graphite over the fractured point with a pencil and the keys started to work.
You said that you didn't see any fractures but I suppose it wouldn't hurt to try to apply graphite on the exposed part of the ribbon on to the suspected line.

ervin

I may as well give it a go!
Thanks.

Bryce

Even if you can't see the fracture, it's good to go over the track with some conducting silver paint, which you can get in most good electronic suppliers. That usually solves most problems.

Bryce.

ervin

Quote from: Bryce on 19:23, 07 April 12
Even if you can't see the fracture, it's good to go over the track with some conducting silver paint, which you can get in most good electronic suppliers. That usually solves most problems.

Bryce.

Thanks Bryce. I'll try that.

Just wondering though, on the 6128 keyboard membrane, the tracks themselves aren't accessible. They have a black coating over them inside the membrane. Will tracing over those with conducting paint work?

In any case, this means that I have to take the dual-foil membrane apart, doesn't it?  :o

00WReX

I think what Bryce is talkng about is described & shown in pictures quite well here (but Bryce may want to confirm this)...

http://www.migman.com/eq/saitek/pc-dash-repair.php

Not a CPC but the idea can be for any connector of this type.

Cheers,
Shane
The CPC in Australia...
Awa - CPCWiki

ervin

Quote from: 00WReX on 05:57, 08 April 12
I think what Bryce is talkng about is described & shown in pictures quite well here (but Bryce may want to confirm this)...

http://www.migman.com/eq/saitek/pc-dash-repair.php

Not a CPC but the idea can be for any connector of this type.

Cheers,
Shane

That's a fantastic link!
Thanks (once again!) Shane. I can't wait to give it a go!
Can't do it tonight though - family Easter duties.  ;D

ervin

Alrighty, I'm now a bit confused!
(Sorry about all of this, but I don't know very much about electronics)

Here is one side of the connector containing the non-working line.


Here is the other side:


Am I supposed to be tracing over the black line in the first picture?
(The black line corresponding to the faulty line).
:-[

Badstarr

Yup the black line!    :)
Proud owner of 464 GTM64 6128 GTM65, GX4128 and a 464/6128 Plus Hybrid a 20 year long ambition realised! :-)

Bryce

Yes, that's exactly what I meant, but just the first centimetre of the track. Sand the tracks with a very fine sandpaper first, it will give you a more reliable result.

Bryce.

ervin

#11
Quote from: Badstarr on 17:46, 08 April 12
Yup the black line!    :)

Cool, thanks.  :)
That's exactly the sort of confirmation I need, to stop me being scared!

ervin

Quote from: Bryce on 22:06, 08 April 12
Yes, that's exactly what I meant, but just the first centimetre of the track. Sand the tracks with a very fine sandpaper first, it will give you a more reliable result.

Bryce.

Fantastic, thanks Bryce.
I'll go and get some fine sandpaper today, and give it a go!

The thought of ruining the ribbon is making me paranoid, but with all the information that you guys have given me, I'm feeling a lot more confident.

00WReX

Remember to be very gentle with the sandpaper, you don't want to rub the contact away or damage the cable...just a light buff is all.
Just like the person in the link mentions...

And definately make sure you have nothing coarser than 800 grade sandpaper...remembering that the lower the number the coarser the sandpaper.

Quick chart - Sandpaper

30 grit
60 grit extremely coarse
80 grit

100 grit
120 grit recommended for general purpose, drywall patches, furniture re-finishing
180 grit

220 grit
240 grit recommended for general purpose, furniture
320 grit

400 grit recommended for fine finishing, polishing, gilding
600 grit

800 grit
1000 grit recommended for fine polishing, hand rubbed finishes and gilding
1200 grit

1600 grit extremely fine. Polishing, jewelry


Cheers,
Shane
The CPC in Australia...
Awa - CPCWiki

Badstarr

If you have a multimeter you will be able to check the continuity on the lines once the fluid has dried. Just be careful you dont scratch the traces with the probes. A cheap and cheerful multimeter will do and will prove useful for many CPC repair projects. If your repair does not solve the problem you can easily use it to check the connections to the AY sound chip and the decoder chip to make sure the problem doesn't  reside there. Either way good luck with the repair!
Proud owner of 464 GTM64 6128 GTM65, GX4128 and a 464/6128 Plus Hybrid a 20 year long ambition realised! :-)

ervin

Quote from: Badstarr on 11:20, 09 April 12
If you have a multimeter you will be able to check the continuity on the lines once the fluid has dried. Just be careful you dont scratch the traces with the probes. A cheap and cheerful multimeter will do and will prove useful for many CPC repair projects. If your repair does not solve the problem you can easily use it to check the connections to the AY sound chip and the decoder chip to make sure the problem doesn't  reside there. Either way good luck with the repair!

Thanks Badstarr. That's exactly the sort of thing I need to know.
I hope it isn't anything other than the membrane ribbon though. If it is, I'll probably be well and truly stuck.  :'(

ervin

#16
Well, looks like I won't be needing this thread any more.
:'( :'( :'(

Thanks everyone for your input and advice.

May I direct everyone's attention to this thread instead?
WTB: 6128 keyboard membrane

Failing that, is it possible to hook up an external keyboard to the 6128 somehow?
I know of the CPCKey project, but there's no way in hell I'd be able to construct something like that.

Badstarr

Still not working?? Is it possible that your CPC has the wrong keyboard installed? I know there are a few different layouts for the CPC, its just a hunch really, maybe someone with a bit more knowledge in this area can advise you. All the CPCs I have, have the same layout apart from my first generation 464 which has different connectors anyway.


Another thing that may be worth trying is to jump the connections from the keyboard connectors on the main PCB to check if the missing letters come up on screen. If they do then you know all you need is a working keyboard, its just a mystery as to why your keyboard doesn't work. Have you checked the membrane inside the keyboard unit?
Proud owner of 464 GTM64 6128 GTM65, GX4128 and a 464/6128 Plus Hybrid a 20 year long ambition realised! :-)

Bryce

There are no other keyboard projects for the CPC and due to the way the CPC reads the keys, all other/new keyboard projects would be as complicated as the CPCKey project.

So what exactly went wrong? Do you have pictures? How about sending the membrane to someone who has experience doing this type of repair? Or have you really destroyed it?

Bryce.

00WReX

What happened ?? This does not sound good at all...
The CPC in Australia...
Awa - CPCWiki

ervin

Well, let's just say I was a bit too thorough, when I gave the connector on the non-working line a "gentle" sanding.

I thought I was exposing the line under the black stuff. Unfortunately, I was actually exposing the plastic ribbon material itself, through the black stuff. And the worst thing is that I did it to all 8 lines. When I realised what I had done, I panicked, and "cleaned" it all up by neatly sanding off the lines from the end of the connector.

I really cannot begin to explain what the heck I was thinking.

Since then, I've tried using a conductive silver pen on the original dead line, and that didn't work.
I haven't tried that on the other lines yet (i.e. the lines that originally worked).

I also tried cutting a long, thing piece of aluminium foil, and sticking it to the good part of one of the other lines, and then into the keyboard connector. The good news is that it made that line of keys work! The bad news is that the same technique didn't work on the originally-dead line. Which of course means that the originally-dead line has a problem elsewhere.

I wish I had just let it be, and put up with my mostly good keyboard!

I reckon this calls for more gratuitous use of the "Cry" smiley:
:'( :'( :'( :'( :'(

Bryce

A bummer, but not the end of the world. I'm sure a replacement can be easily sourced.

Bryce.

ervin

Quote from: Bryce on 15:21, 10 April 12
A bummer, but not the end of the world. I'm sure a replacement can be easily sourced.

Bryce.

I really hope so.

I know that in the grand scheme of things, this is one of those "meh, so what?" kind of things, but it is indeed a bummer, as I've wanted a real CPC for such a long time, and now that I've got my hands on one, I've messed up.

Anyway, I won't give up.
8)

00WReX

 :o :o :o

Ahhh...nooooo...


:( :( :(


Don't beat yourself up too badly (easier said than done, I know), these things do happen though...It will all turn out OK.

I will definately keep a good eye out for one...my 6128's are functional, so a bit reluctant to dismantle a worker, but one will definately come up that's for sure...


Trouble is, I suppose it's still not 100% proven that it's the membrane that's the issue...well, it is now but you know what i mean.


Shane.
The CPC in Australia...
Awa - CPCWiki

ervin

Quote from: 00WReX on 15:36, 10 April 12
:o :o :o

Ahhh...nooooo...


:( :( :(


Don't beat yourself up too badly (easier said than done, I know), these things do happen though...It will all turn out OK.

I will definately keep a good eye out for one...my 6128's are functional, so a bit reluctant to dismantle a worker, but one will definately come up that's for sure...


Trouble is, I suppose it's still not 100% proven that it's the membrane that's the issue...well, it is now but you know what i mean.


Shane.

Yep, I'll keep my eyes pealed for one!

Ironic isn't it? In trying to fix what *may* have been a small problem, I've created a much bigger one.

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