Plus Model Keyboard Membranes

[terriblefire]

Hi,


Seems my 6128+ keyboard is starting to go. Several keys have stopped working. Does anyone know if there are replacement membranes available.


I guess if not i could look a project to make a replacement.

[Skunkfish]

Try cleaning the socket where the membrane connects to the main board. That solved the issues with my Plus's keyboard that even a new membrane didn't fix.

[terriblefire]

Will give that another try.

[gerald]

Hi,


Seems my 6128+ keyboard is starting to go. Several keys have stopped working. Does anyone know if there are replacement membranes available.


I guess if not i could look a project to make a replacement.

Have a look there : http://quasar.cpcscene.net/doku.php?id=electronique:reparation_clavier_cpc_plus
Basically just remove the resistor network that pull-up the keyboard rows.
It is not needed with the AY8912 which is usually monted on the Plus (it IS needed with the AY8912A)

[Skunkfish]

Wow, thanks Gerald. I didn't realise that was the cause of all of the 6128 Plus keyboard issues!
My issues had started to return, I will give this a try ASAP!

[gerald]

Wow, thanks Gerald. I didn't realise that was the cause of all of the 6128 Plus keyboard issues!
My issues had started to return, I will give this a try ASAP!

Well, the resistor network is not directly responsible for the issue, but it worsen it.
The ageing keyboard membrane get its resistance increasing with time, which makes a voltage divider with the pullup up to a point where the AY is no more able to make the difference between a keypress and no keypress.
Removing the network make the matrix parasitic resistance relatively far lower compared to the AY integrated pull up, and make the detection by AY possible again.

As said on the linked page, the resistor network is not needed when a AY8912 is mounted.
And removing it does not solve cracks related issues 

[Skunkfish]

Wonderful, I can now control+shift+escape to reset for the first time in a while! 

[GUNHED]

Is it enough to cut one wire of the network? If yes which one?

[Bryce]

Is it enough to cut one wire of the network? If yes which one?

You would need to remove the network completely. Technically removing the common ground of the network might seem like the solution, but then you are just giving the electrons an alternative path to ground which may have unintentional consequences.

Bryce.

[GUNHED]

Well, then it needs to go completely. Did you remove yours too?

[megachur]

just to share with you my experience this morning with the 6128+ (version G) keyboard issue :

at first, no key are responding.

disconnection / cleaning / reconnection of the 2 keyboard cables
-> some keys work again but not all
for example : the keys 't' gives several keys 'tyuio '.


But if I press a key for a while, we have the combination of keys + a key that is repeated ...t -> give 'iyt' and wen pressed for a while : 'iyttttttttttttttttttttttttttt'

I removed the NR02 resistance... nothing better


I disassembled the mechanical keyboard, wiped a cloth on both sides of the membrane ... I then reassembled it, being careful to align the 2 holes with those of the metal plate ... everything works once connected !  

[GUNHED]

Well, then I dare to do this kind of surgery too...