Re: Keys 56tyghvb not functional


"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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