ZX spectrum after 20 years in box

[fouracre]

Today I tried to use my ZX Spectrum after 20 years or more in it's box. After a little while I managed to get a TV tuned to it and get the Copyright message on the screen. And that's it. Pressing the buttons does nothing.

Is it as obvious as the keyboard is done, or is there something I can do to ressurect it?

[paul.brett]

This is nearly always due to the fragile keyboard membrane used by these early Sinclair computers. new membranes can be had from Ebay, and they are quite easy to fit.

Paul.

[JimmyDeath]

Mind you if it's the original spectrum with the rubber keys it is quite difficult to remove the aluminium cover and refit it without the end result looking as if it has been in a car crash. Don't suppose anyone re-manufactures them as well?

Regards, James

[G8VAT Wolfman]

If you need to get one of those ally covers off, heat it with a hairdryer until reasonably hot.

If this is a later Spectrum plus then the clamps for the keyboard tails wilt with age, remove them wipe the inner surfaces of the tails, and reclamp with an added piece of paper under the clamp.

[DragonForce]

Right, it depends on what you have there.

First thing to suspect on a non working keyboard is the membrane itself - you can get these from eBay for around a fiver, plus post. However, since you say that all the keys are not working, it could be the ULA that's at fault.

The keyboard membrane usually fails in a localised area, taking out just a row or a column of keys. For the whole thing to be dead suggests either a membrane cracked along all the connections (where it connects to the motherboard via a pair or contact strips) or the ULA isn't happy. Either way, it is a simple job to repair it.

First get a new membrane and try that - it's almost certainly down to that.

To remove the metal template, look to see if it's held on with small metal clips, or simply stuck down with single sided tape. Metal strips, just prise them up gently with a screwdriver and be careful not to bend or distort the metal template.

If it's held down with double sided tape, a hot hairdryer is the tool to use.

If you try a new membrane and it doesn't work, then you will need a new ULA chip. We will deal with that if and when the problem arises.

Just a few tips - once you have your Spectrum working again, recap it - those electrolytic capacitors are 30 years old now, and they can cause no end of problems, from random resets to a pretty lousy screen image being produced.

Measure the PSU output voltage - it will be more than the 9V it's rated at. I'd suggest that if it is much above 12 volts, open up the case and add a 3A diode (or maybe two) in series with the power lead - that will reduce the voltage down by .7 of a volt or so and save the 7805 chip from getting so hot. Hot regulator chips are not healthy for keyboard membranes, they go brittle and will crack - as you have probably just discovered. Whilst you have the PSU case open, swop the old smoothing cap for a nice new one.

If you have a Spectrum Plus machine, then you are talking a whole different ballgame as far as fitting a new membrane is concerned.

@Jimmy - yes, you can also buy a new keyboard template, they are almost identical with the original templates, and are very good quality. Ebay again....

Edited to add: On the Spectrum, the centre pin of the 2.1mm power jack is NEGATIVE - do not be confused by any tracer lines on the cable. I've seen a red tracer used on these things to signify the NEGATIVE lead, and it gets really confusing. This is true of the rubber keyed machine, the Spectrum Plus and the original Sinclair 128 (heatsink on the right hand side, looks like a toast rack) and the Amstrad grey +2. The BLACK +2 is a +2A, and is basically a +3 without the disk drive electronics - these two machines use a dedicated power supply and has a multi-pole connector plug.

[paul.brett]

There is a well known and fairly simple hack you can make to the Spectrum to convert the video output to go into a modern TVs Video-in socket, that gives a fantastic picture with no faffin around with 'tuning'.

[Refugee]

I once did it to a ZX81 for a mate many years ago.
The whole PCB was installed into a metal keyboard complete with a power supply and a BNC socket provided at the back. I think the modulator was removed. It was used on an old CCTV monitor.

[DragonForce]

Yes, the composite video mod works pretty well.

There is more than one way to go about it though, this one uses a small buffer amp.

http://www.dragonchat.net/Alchemist/...site_video.htm

[SiriusHardware]

One thing I'd suggest is: Take the lid off - careful lifting it off because the keypad ribbon is delicate - carefully ease the keypad membrane ribbons out of the sockets on the PCB. It is essential not to put sharp kinks or folds in the keypad ribbons.

Now: With power on, try using a low value resistor (say 47 or 100 ohms) to momentarily join randomly chosen pins on one keypad PCB connector to randomly chosen pins on the other keypad PCB connector.

Does that cause characters to be 'typed'?

If yes, your ULA is probably OK, go ahead and order a keypad membrane.

If not, there's no point in ordering a membrane, the problem is on the PCB.

[Mad Mal]

I would say the membrane keyboard has perished. The plastic film these were made of also tended to degrade, though more often than not it was the metallic conductors (Cracking in the tracks or oxidisation changing the resistance). Don't bin it, these machines are sought after by Tech Museums and TV/Theatre Prop companies.

[SiriusHardware]

I think the same outfit which supplies new Spectrum key membranes also had some aluminium keyboard legend / cover plates made as well, should you end up needing one. (Just realised: This is quite an old thread, but the information in it remains useful).