Having bought a few ZX Spectrums - it was only a matter of time before I found one in need of some serious attention.

This one wouldn’t boot properly, just displaying a pattern of multicoloured blocks in the main screen area. On one occasion it seems to jump into the load/save routine and the border started flashing with the accompanying noise from the speaker. Pressing a key caused the sound to stop momentarily. These symptoms were enough to convince me that the CPU and ULA were working fine - and it was likely that the fault was in the lower 16KB of memory.

First job was to modify the video for composite video. There is a very well known simple fix which is shown in the picture below.

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 PCB where the left connection used to be. This is fed through the spare plastic surrounded hole nearest the phono plug and soldered to the phono plug’s central pin. Thats it! There are other possibly better solutions which I will try when I get a chance.

Next job was to remove the faulty 8 type 4116 RAM chips from the PCB. Rather than buying replacement 4116 chips I opted for a brand new memory board which was being advertised on “Sell My Retro” website (search for “spectrum 4116”).

Next - I soldered in the replacement DIL sockets. The memory board can be soldered direct to the motherboard PCB - but if sockets are used they need to be these type and not the more expensive turned pin variety.

After that I just had to press in the new memory board. The machine booted up just fine and after reattaching the keyboard I was able to check that all 48K was working properly.

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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