Issue 3 Spectrum 48K dodgy output

User avatar
Tiger
Posts: 88
Joined: Tue Sep 01, 2020 10:37 am

Re: Issue 3 Spectrum 48K dodgy output

Post by Tiger »

As you described the fault in my humble opinion there is something with IC 14 (LM1889) or the parts around this: X2 (may age and therefore be out of tolerance), R43-47 (R43 -3K- and 44 -5K1- must have low tolerance -2%), C37-39, C65, C40, C72 (16pF 5%), C52-53, R76-R77. Sometimes it is only a little bad soldered connection but sometimes it is really IC 14.
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Issue 3 Spectrum 48K dodgy output

Post by Lardo Boffin »

I have ordered an X2 and IC14 so will fit them and see if that helps.
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: Issue 3 Spectrum 48K dodgy output

Post by Lardo Boffin »

Well, progress of sorts.

I have replaced X2, no change so was probably Ok.

I then replaced IC14 and no immediate change but after about 20 seconds the TV that showed diagonal stripes resolved into a pretty reasonable picture.

I tried this on my HD LCD TV (that was colour changing) and it is much better but still not right. The background is consistently white now but the text alternates between blue and black and there are interference patterns every few seconds.

If I let the computer cool down for a few minutes it takes a while (20 seconds or so) before the stable picture comes back.


Argh!
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: Issue 3 Spectrum 48K dodgy output

Post by Lardo Boffin »

I just plugged in SmartCard and loaded Manic Miner.

No sound! I don’t think me and this Spectrum and destined to get along.

Manic Miner actually looks ok if you can get past black being blue…
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: Issue 3 Spectrum 48K dodgy output

Post by Lardo Boffin »

1024MAK wrote: Mon Nov 08, 2021 10:21 pm
Lardo Boffin wrote: Mon Nov 08, 2021 10:05 pm Me too! I will try the ULA from the dodgy speccy in the good one to see if it works there - should have done that first time around. :oops:
Maybe we’ll make a fault finder out of you yet! :lol:

If you have a spare working machine, it’s alway worth thinking about moving the suspect chip by swapping it into the known good machine, then if the fault moves with the chip…

Mark
I moved the ULA from the dodgy Spectrum to the known good one and the picture is fine and it produces sound ok. Not the ULA then!
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: Issue 3 Spectrum 48K dodgy output

Post by Lardo Boffin »

Thanks to this post I now have sound!

viewtopic.php?p=37745#p37745

I changed the socket of the ULA but still a rubbish picture. :evil:
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: Issue 3 Spectrum 48K dodgy output

Post by 1024MAK »

I’ve put some test results in this post which may help ;-).

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: Issue 3 Spectrum 48K dodgy output

Post by Lardo Boffin »

1024MAK wrote: Tue Nov 30, 2021 6:15 pm I’ve put some test results in this post which may help ;-).

Mark
Thanks! I will have a look and measure when I get chance.
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