Single key (space bar) not working on CPC6128 renovation. Mechanical problem?

[jknams]

Hello all - this is my first posting on this forum...

I am 'reviving' a CPC 6128 which I have been given. I am fairly knowledgable in electronics etc. and have done a fair bit of reading beforehand. The machine is question seems to be mostly working but I have a keyboard question (different from the usual I think)

Almost all of the keys seem to be working, except for: the Space key.

Given the matrix nature of the wiring, I originally thought that this means a membrane problem. However, I have managed to source a new membrane ... and the problem remains!

This makes me think that it must be a mechanical issue. I will start to investigate further along these lines, but I am looking for suggestions from those more experienced with this machine. Is it the small spring 'inside' the underside of keycap which forces the membrane layers together? Do these deteriorate? Or should I be looking elsewhere?

    Thanks for any ideas
    Jon N

[Bryce]

Hi Jon,
      my first question would be, does it feel right. ie: if you press it at one end, does it still go down evenly along the whole length or does it jam. If not, the metal clip under the key might be missing or wrongly installed. The outer springs raise the key, the small inner spring is what pushes the membrane.

Bryce.

[jknams]

Hi Bryce
    yes, the key presses evenly.

On close examination it does look as though the small underside spring for this key might be a bit compressed compared to others. I am going to take a look at stretching it a little...

I am a bit surprised that I have not seen this mentioned as a possible failure mechanism before though. If the reliability of the keypresses relies on the length of those springs (give or take 0.5mm, say) I would have thought this would be a big issue.

Thanks, J^n

[Bryce]

Hi Bryce
    yes, the key presses evenly.

On close examination it does look as though the small underside spring for this key might be a bit compressed compared to others. I am going to take a look at stretching it a little...

I am a bit surprised that I have not seen this mentioned as a possible failure mechanism before though. If the reliability of the keypresses relies on the length of those springs (give or take 0.5mm, say) I would have thought this would be a big issue.

Thanks, J^n

It's not something that happens that often, but I did once encounter a similar problem, because the CPC had been stored for a long time with something (a heavy book) placed on top of the keyboard.

Bryce.

[jknams]

Hi Bryce
    yes, the key presses evenly.

On close examination it does look as though the small underside spring for this key might be a bit compressed compared to others. I am going to take a look at stretching it a little...

I am a bit surprised that I have not seen this mentioned as a possible failure mechanism before though. If the reliability of the keypresses relies on the length of those springs (give or take 0.5mm, say) I would have thought this would be a big issue.

Thanks, J^n

It's not something that happens that often, but I did once encounter a similar problem, because the CPC had been stored for a long time with something (a heavy book) placed on top of the keyboard.

Bryce.

Hi Bryce - that is an interesting thought, thanks. It is possible that that is what has happened to this CPC 6128.

Hopefully given this understanding I will be able to sort it out.

Regards, J^n