Sinclair ZX Spectrum 128 +2B: Part 1
24It's about time I checked if this machine worked. I think I originally obtained it in 2021 but had no way to output video at that time ... no little GBS8200 boards, no RGBS cables.
I did confirm the PSU was working: +5VDC and ±12VDC ... I replaced the 7812 with a modern, switching version apparently in April 2021.
So first thing today was to create an RGBS cable for the 8-pin DIN interface ... once I obtained some 8-pin DIN plugs. If pin 8 wasn't used for the "blue" signal that I could've gotten away with using a 7-pin DIN plug instead.
The case says "Spectrum +2" but it's actually a +2A (at least) ... this is indicated by the black, rather than grey, case and the +2A stamped on the bottom case. However I believe this is actually a Spectrum +2B as it contains a Z70833 motherboard instead of a Z70830.
It is important to confirm which model because the video pinout differs between the original 128/+2 and the later +2A/2B.
The 8-pin DIN on the +2A/2B includes RGBS + mono audio as well as two sources of 12V.
I just made a cable up for the RGBS signals (pins 2/4/6/7/8) and connected a speaker to the separate sound jack:
Pin 1 = 12V (not used)
Pin 2 = ground
Pin 3 = audio (not used)
Pin 4 = composite sync
Pin 5 = 12V (not used)
Pin 6 = green
Pin 7 = red
pin 8 = blue
I confirmed the orientation of the plug by checking where the 12V levels were ... pins 1 & 5.
And yes, the machine does work! However no response from the keyboard.
I dismantled the keyboard, pulled the two halves of the membrane apart and wiped down with some IPA (isopropyl alcohol, not the beer). Carefully matched the two halves back together, reassembled ... and the keyboard was working!
I loaded a game via the built-in Datacorder and it loaded fine ... although kept playing after the game started ... ?
So far, so good.
There are additional improvements that apparently can be made - I'll look at those next:
[1] Improve sound output quality
[2] Convert TV modulator to composite output
[3] Convert Sinclair joystick ports to Atari standard
[4] Try to get my DivMMC to work
https://spectrumforeveryone.com/technical/
https://zxnet.co.uk/spectrum/+3sound/
https://www.retrocomputershack.com/SCART-DESIGNS/Spectrum+3/index.html