ZX81 rebuild

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin »

Putting in Andy’s ULA solved the screen jump issue I was having in hi res games. Nice one Andy!

Original parts left:-

Motherboard - can’t do much about that
6.5 MHz resonator
Case - might try and make a custom one

I still need to get hold of a UHF modulator for less than £20 and put in an ear and mic socket.

C74D30EF-8958-4951-BC8A-D2DCD9E63829.jpeg
4671F3CC-FD40-4099-9021-B4FA522B5513.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
McKlaud
Posts: 337
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: ZX81 rebuild

Post by McKlaud »

Good work. :mrgreen:

BTW I’ve got a few RF modulators in my spare parts drawer. Some of them should work fine, the others are broken. If you need one drop me a line.
Claudius
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User avatar
1024MAK
Posts: 5102
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK »

McKlaud wrote: Tue Nov 20, 2018 12:21 pm Good work. :mrgreen:

BTW I’ve got a few RF modulators in my spare parts drawer. Some of them should work fine, the others are broken. If you need one drop me a line.
Go on, send him a broken one. He loves fault finding on this Zeddy :mrgreen: :lol:

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.
McKlaud
Posts: 337
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: ZX81 rebuild

Post by McKlaud »

Hi Mark ;)

Now you can laugh out loud, because Lardo asked me for a faulty unit :mrgreen: :mrgreen: :mrgreen: :mrgreen:
Claudius
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Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin »

1024MAK wrote: Tue Nov 20, 2018 4:21 pm
McKlaud wrote: Tue Nov 20, 2018 12:21 pm Good work. :mrgreen:

BTW I’ve got a few RF modulators in my spare parts drawer. Some of them should work fine, the others are broken. If you need one drop me a line.
Go on, send him a broken one. He loves fault finding on this Zeddy :mrgreen: :lol:

Mark
I aged 5 years in the time it took me to get this one working! :shock:

I only need a broken one for the case. 8-)
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: ZX81 rebuild

Post by Lardo Boffin »

I just got one of these off eBay, possibly from someone on here?

733632C1-0559-4558-B954-A604D17E48F9.jpeg

Loving the keyring! Nice bonus. 8-)
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: ZX81 rebuild

Post by Lardo Boffin »

In place and working but I need to add the switch so I can play with the other ROM options.

D850C639-0B20-4AFB-909F-8E0D2A72BDB6.jpeg

ROM options:

Bugged ROM (the earliest official Sinclair ZX81 ROM with mathematical errors)

Standard ROM (the normal Sinclair ZX81 ROM that was fitted to almost all models)

Standing on the Shoulders of Giants ROM (improved 'Standard' ROM by Geoff Wearmouth, 2003)

Husband Forth (The Forth programming language for the ZX81 by David Husband, mid 1980s)

ASZMIT (Assembler ROM)

ZX81x2 (an improved and faster ROM AKA 'Big Bang' from 2018 by Zsolt Gaal)
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
Moggy
Posts: 3231
Joined: Wed Jun 18, 2008 2:00 pm

Re: ZX81 rebuild

Post by Moggy »

A most excellent zeddy you have there Lardo. :D
Just for clarity there is at least one known maths operator bug in the h4th ROM which may or may not be present in your ROM depending on who programmed it. If it come from the German lads then it's probably not present, a thread here for clarity.

viewtopic.php?f=3&t=2632&p=28741&hilit=h4th+bug#p28741


The manual for the Azmic ROM can be found here.

viewtopic.php?f=7&t=1503&hilit=azmic+rom&start=10
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin »

Moggy wrote: Fri May 15, 2020 5:55 pm A most excellent zeddy you have there Lardo. :D
Just for clarity there is at least one known maths operator bug in the h4th ROM which may or may not be present in your ROM depending on who programmed it. If it come from the German lads then it's probably not present, a thread here for clarity.

viewtopic.php?f=3&t=2632&p=28741&hilit=h4th+bug#p28741


The manual for the Azmic ROM can be found here.

viewtopic.php?f=7&t=1503&hilit=azmic+rom&start=10

Thanks for the links Moggy!

Forth up and running. 8-)

66E9231C-6CEC-472D-8823-F7B71963AF43.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: ZX81 rebuild

Post by Lardo Boffin »

Soldering the wires to the switch was an absolute nightmare.

Z80 for scale....
38408AA7-D70C-490D-BB7E-9AB5495AE19F.jpeg
My eyesight is nowhere near good enough any more.
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
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