Re: Keys 56tyghvb not functional

I don't think the 81 cooked as well as the Spectrums did, and I also have a
feeling that the rubber keys of the Spectrum did make some membranes crack
where the key pads were, making of intermittent keys.

The worst of all was the + and 128 membranes which had more layers, had
connections made by plastic clamps and the keys damaged the membranes as
well as the sharp bend and heat issues.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email: briang1@xxxxxxxxxxxxxxxx
______________________________________________________________________________________________________________


"Simon Holdsworth" <susan.holdsworthNO@xxxxxxxxxxxxxx> wrote in message
news:bCAAe.29883$y86.8735@xxxxxxxxxxxxxxxxxxxxxxx
>
> "Ian Rawlings" <news05@xxxxxxxxxxxxx> wrote in message
> news:slrndd5gnn.ega.news05@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Hello peeps, any likely causes here? I've just bought an '81 on ebay
>> advertised as "fully working" only to find a third of the keys don't
>> work (am chasing the very incommunicative seller). I suspect a common
>> wire has gone green. The keys 56tyghvb are not functional, forming a
>> vertical-ish line down the keyboard.
>>
>
> The keyboard on the '81 (and on early Spectrum models) uses a matrix
> scheme with each row of keys being split in half, into groups of five,
> making 8 groups of 5. The wiring for the matrix is just conductive tracks
> printed on a flexible plastic backing. There are two strips that come off
> the keyboard matrix, one with 8 tracks, one for each group, and one with 5
> tracks, one for each key in each group. These strips have to be bent
> round to connect to the motherboard, and where they bend they eventually
> perish and crack. Looks like the strip with 5 tracks has cracked and
> broken the connection of one of the tracks, causing those keys on the end
> of each group to fail to work. This is an extremely common occurrence.
> The best solution (although not easy...) is to get a replacement "proper"
> keyboard, that has a ribbon cable connector that is not prone to the same
> sort of failure.
>
> Incidentally, I've seen proportionally a lot more Spectrums with duff
> keyboards than ZX81's - probably 75% of Spectrums and only anout 25% of
> ZX81s... I guess there was a different manufacturer, or different
> materials? Maybe the ZX81s got less use and therefore less heat, and so
> perished less on average?
>
> Cheers, Simon
>
>


.

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