Spectrum 128K +2A RF sound issues

Post Reply
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Spectrum 128K +2A RF sound issues

Post by Lardo Boffin »

Hi all

I have an otherwise lovely +2A that does not produce sound on the RF out to the telly (well, it produces a hiss as though not tuned in, which it is). If I use a SCART then I get a great picture and sound. It is the later revision of the +2A that has the corrected sound circuit.

I have recapped it (including the tape drive which was fiddly) and done the RGB ghosting fix (from https://spectrumforeveryone.com/technic ... compliant/) which just involves changing a resistor.

Any idea what might be wrong? Its not a big deal as I can use scart but I am curious!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
User avatar
1024MAK
Posts: 5102
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Spectrum 128K +2A RF sound issues

Post by 1024MAK »

Maybe someone has previously removed the ceramic capacitor (C24) that feeds sound to the RF output?

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum 128K +2A RF sound issues

Post by Lardo Boffin »

Thanks Mark - will have a look when I get chance.

Here is the PCB after a clean up and recap:

F7D8DC3E-A23D-49CB-A1B9-FEBC9067D728.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum 128K +2A RF sound issues

Post by Lardo Boffin »

I found C24 intact:

2A33153D-B02C-4AAF-9832-D4F18D12C40F.jpeg

But while hunting for C25 I noticed C53 has been snipped off. :shock: Is that anything to do with sound or just a coincidence?

15F6C05D-B7C4-4FD2-B6C1-DD84DA511D2D.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Post Reply