There is a lot of speculation as to why this error occurred – either the transistor type was swapped to 2N3904 at some point and the silkscreen was not updated, or the designers were working with an incorrect version of the 2N3904 datasheet. TR4 is part of the composite video circuitry, TR5 is responsible for generating the RGB vertical sync, and TR7 is responsible for generating the ULA IOREQ signal, so having all of them reversed causes serious video problems. Spectrum 128k+2 composite video output from factory (yuck!).įirstly, the Z70500 ISS3 mainboard has a major design fault where three 2N3904 transistors (TR4, TR5, and TR7) are marked incorrectly on the PCB silkscreen and, as such, were installed backwards at the factory.

The ZX Spectrum 128k+2 (and upon extension the 128k+, its predecessor) suffer from various design flaws which affect their video quality. #4: Replace all the electrolytic capacitors on the mainboard and tape board.

#3: Replace the original connectors with new parts. #2: Fix the audio balancing issues associated with the factory ZX Spectrum 128k+2. #1: Fix the video output issues associated with the factory ZX Spectrum 128k+2. There are several steps which I like to take when performing a complete restoration on a Spectrum, which include fixing factory or age-related problems, and future-proofing.Īs such, I planned out the servicing, preventative maintenance, and upgrades that I wanted to perform, as follows: Initial testing – computer boots normally, with noticeable artefacts on composite video. ZX Spectrum 128k+2 interior before restoration.Īfter checking that the PSU was working OK, I did a quick power-on test plugged into the composite video port and the computer seemed to boot up fine. The Spectrum seemed to be all original, and featured a 1986 Z70500 ISS3 mainboard with 128 KB of factory-installed RAM – the ULA, CPU, and ROM were socketed. Sinclair ZX Spectrum 128k+2 before restoration. The Sinclair ZX Spectrum 128k+2 was the first machine produced by Sinclair following their takeover by Amstrad, and was a replacement for the ZX Spectrum 128k+ – the 128k+2 was a quick and crude redesign of the 128k+ hardware but in a larger and re-styled grey case, featuring an internal tape deck similar to the Amstrad CPC 464. The machine was in good condition and came with several accessories and its original box, however it was sold as “untested”. A while back I got my hands on my first Sinclair ZX Spectrum 128k+2 (grey), yet another 1980s 8-bit computer to add to my collection.

Sinclair zx spectrum rom set