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2nd ZX Spectrum repair

This Spectrum had taken a few knocks - but at least it booted. The keyboard was dead however. Apparently it had been dropped some point in its past and the faceplate was being held on by black PVC tape.

An interesting point you can see in the photo is how the spectrum stripe is made up. The red has worn away and you can see that it was painted on top of a larger strip of yellow. I did consider repainting this stripe - but the faceplate was in poor condition so I was hoping to replace it.

ZX Spectrum in non working state

The keyboard membrane proved to be completely cracked so it would need replacing. I also noted that it had suffered a memory fault in the past as one of the upper memory chips was now socketed.

Issue 4B Spectrum motherboard with socketed RAM chip

Again the first job was to modify the video for composite video. This time I tried the single transistor fix. I had previously tried it on my other Spectrum without success - but it proved to be an issue with the TV and not the fix.

The top is prised off the modulator and the wire to the central pin of the phono connector is cut.

The 2 connections going into the modulator box (bottom of photo) are also cut.

A wire (in the case yellow) is soldered to the Emitter of a small NPN transistor. This yellow wire is fed through the spare plastic surrounded hole nearest the phono plug and soldered to the phono plug’s central pin.

The transistor’s Base is soldered to the video connection on the PCB (this was the wire that was cut which went through the ‘middle’ hole in the modulator).

The transistor’s Collector is soldered to the PCB connection for the other cut wire - on the right in this photo. This is the 5V line which originally powered the modulator.

I found this info on Youtube - and will hopefully put together a better page on it when I have some more time.

Modulator after transistor composite video fix

The keyboard membrane was beyond repair - but I had another - the one from my original 16K ZX Spectrum from 1982. This membrane had a fault but I thought it was worth trying to fix it. Anyway I trimmed the obvious damage off the end and tried reinserting it. All keys did respond but the ‘0’ key kept getting stuck down. This is a rather different and rarer problem - so I decided to use one of the spare new membranes I had bought on

Membrane tail trimmed to remove damage

The membranes tails can crack when being inserted unless they are stiffened. Neither my old membrane nor the one which came with this Spectrum had the small plastic stiffers attached so I could not reuse them. I cut new ones from an old business card and stuck them on with double sided sticky tape.

Membrane tail fitted with a cardboard stiffener

Another thing I noticed was that the faceplate had once been fitted with the small brass tabs designed to hold it in place. They were completely missing - also indicating that it has been worked on in the past.

Evidence of brass fixing tabs

As I write it is possible to buy brand new replacement faceplates on SellMyRetro - but I was fortunate to find a decent one cheaply on ebay. In the picture below you can see the double sided sticky tape applied to stick it in position. I had also thoroughly cleaned the case and the keyboard mat.

Fitting the keyboard

Once I had fitted the keyboard I was able to test the memory which fortunately was okay. There are still a few cosmetic things I can do - but it has turned out as a functional and clean example.

Finished and re-assembled


All text and images Copyright © 2000-2014 Roland Givan, unless otherwise stated. All Rights Reserved. Game artwork copyright their respective publishers.

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