This machine was probably build in 1983/Q1 as 16K ZX Spectrum, and was upgraded by Sinclair to 48K around 1983/Q4.
Instead of a serial number, the word “Upgraded” is embossed into the case. It means that the board was originally inside a ZX Spectrum “rubber keys” case. The system was then upgraded to a “ZX Spectrum Plus” in 1984 or later. This would explain why I found an “Issue Two” board (with a twisted heatsink) in a ZX Spectrum Plus case. Sinclair sold upgrade kits, but this machine had a German warranty sticker, so the upgrade was done by Sinclair.
Known Issues
Speaker is very silent.
Cannot load from tape, signal is too weak.
Restauration Works
Restauration was carried out in January 2023.
-5V and 12V were missing. Fixed by replacing TR4 and D16. Strangely, the system was still starting without these voltages.
Recapping, Traco DC/DC converter, Composite Mod.
Case cleaned.
Membrane connector was broken off, so the membrane was replaced with a new replica.
Display had a greenish tint and a strange horizontal raster. Repaired by replacing IC14 and VR1.
Applied a heatsink to the ULA.
Perfect calibration of video quality and crystals.
History
2023-01-22:
Replaced IC14 with a socket and a NOS LM1889N. Image quality was slightly improved.
Replaced VR1, which finally fixed the issue with the discoloration.
Reset wire was too short after recapping. Replaced with a new wire.
On the keyboard, the “ASDFG” keys did not respond. Replaced D3, but that didn’t help. Fixed the issue by putting some tape behind the membrane contacts.
Applied a heatsink to the ULA.
Reassembled the system. Refurbishment is now completed.
2023-01-21:
Cleaned the case
New keyboard membrane, as the connectors of the old one were broken off
Composite mod
Replaced 7805 with Traco Power DC/DC converter
-5V and 12V were bad, fixed by replacing TR4 and D16
Recapped
Diagnostics detected a 16K model. Checked all chips related to upper RAM, but eventually found a drop of solder as cause. IC16, IC17 and IC21 were detected as faulty by the Retro Chip Tester, but seem to work fine in the machine, so I kept them.
Display has a greenish tint and horizontal disturbances. Tried to fix it by replacing D15, TR1, TR2. Also swapped ULA, but it didn’t change anything.
Cleaned in IPA bath. Broke off speaker when I tried to bend it up so it won’t have contact to IPA, and resoldered it after the bath.
