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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 5th Aug 2010, 10:52 am   #1
dishmaster
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Default Sinclair Spectrum ZX

I need help to fix this. It all works apart from the 1, 2, 3, 4 and 5 buttons. So I can't get it to do anything. Please help.
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Old 5th Aug 2010, 11:21 am   #2
julie_m
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Default Re: Sinclair Spectrum ZX

Sounds like a faulty keyboard membrane. 1, 2, 3, 4 and 5 are all in the same scan group. Check the 8-way connection. If you're very lucky, it will be nothing more than a dry joint where the connector meets the motherboard; if you're unlucky, it will be a crack in the membrane.

Replacement membranes do exist, but it's hardly worth sourcing one when you can make up an improved keyboard using tactile switches (available at very reasonable prices from the usual place).
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Old 5th Aug 2010, 7:54 pm   #3
G8VAT Wolfman
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Default Re: Sinclair Spectrum ZX

If it's the part of the membrane that goes in to the board connector that's worn away, you can trim a little off the end of the membrane strip to enable a new part to reach into the connector.
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Old 5th Aug 2010, 8:40 pm   #4
David G4EBT
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Default Re: Sinclair Spectrum ZX

As has been said, the membranes were notorious for cracking across the tracks - they'e only conductive silver paint deposited onto plastic - and unless someone has already shortened the membrane connection before, you can trim a bit off with a pair of scissors.

But if that fails, new membranes for the original rubber-keyed spectrum aren't exhorbitant - eg, £8.50 and £2.75 P&P from this source, which can supply bits for other Sinclair PCs (ZX81, QL etc) and other makes:

http://www.rwapsoftware.co.uk/membranes.html

I'm not recommending this supplier, with whom I've had no dealings - I'm just pointing out one of many sources, and putting the cost of a DIY replacement membrane into perspective.

Hope that helps.

David.
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Old 6th Aug 2010, 10:38 am   #5
dishmaster
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Default Re: Sinclair Spectrum ZX

Thank you for all your replies I will try this out and let you know.
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Old 7th Aug 2010, 11:56 am   #6
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Default Re: Sinclair Spectrum ZX

Quote:
Originally Posted by ajs_derby View Post

Replacement membranes do exist, but it's hardly worth sourcing one when you can make up an improved keyboard using tactile switches (available at very reasonable prices from the usual place).
So do I solder the wires from the membrane to the tactile switches?
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Old 7th Aug 2010, 1:42 pm   #7
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Default Re: Sinclair Spectrum ZX

You can't solder to the membrane. But you should be able to force an offcut of Veroboard into the motherboard connector where the membrane plugged in.

What you'd have to do is, cut a piece of Veroboard to the right size and mount the switches on that at the correct spacing so you can use the original rubber keys to press on them (it's easiest to work "upside down", soldering them to the track side). The way these switches are made, they have two terminals connected to each switch contact, which makes the design a bit easier. There are 8 scan groups of 5 keys (half a row) each, and the column matrixing is done from outside to inside. The leftmost keys on each left-hand half-row are common with the rightmost keys on each right-hand half-row and so on, working inwards.

If you need a diagram, I'll sketch one and scan it in.
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Old 10th Aug 2010, 9:57 am   #8
dishmaster
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Default Re: Sinclair Spectrum ZX

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Originally Posted by ajs_derby View Post

If you need a diagram, I'll sketch one and scan it in.
Could you do that for me please? it would be a great help. I forgot to tell you that mine is a 48k + with the hard keys.

Last edited by Darren-UK; 10th Aug 2010 at 11:03 am. Reason: FSK.
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