ZX81 Video Mods and Hi-Res mods

Early home computers aren’t known for their crisp video displays. To save on costs and ensure maximum connectivity the majority of the home computers from the early 80’s used a RF modulator to connect to the TV’s of the day via their aerial / antenna socket. In fact most TV’s from this era only had a aerial / antenna connector. There was no composite video, no component video and no SCART video until much later.

Today thankfully, things are much different. Every modern TV is full with video interfaces and connectors. But not all modern TV’s are able to display video from these ancient computing devices. So a little help is needed from us to made these things work together. Here’s some links for the ZX81.

• ZX81 Video Composite modification:

Composite mod voltages
https://www.sinclairzxworld.com/viewtopic.php?f=10&t=622

ZX81-Composite-mod-PCB
https://github.com/gpimblott/ZX81-Composite-mod-PCB

Zx81_2_Composite
https://github.com/Th4nat0s/Zx81_2_Composite

ZX81 Video Conditioning
http://zx.zigg.net/misc-projects/ZX81_Video_Conditioning.pdf

ZX81 Video Conditioning
https://www.youtube.com/watch?v=1irH3KuGyl0

ZX81-Composite-Video-Mod
https://github.com/Alleged-Geek/ZX81-Composite-Video-Mod

ZX81 Composite Video Modification
http://blog.tynemouthsoftware.co.uk/2016/11/zx81-composite-video-modification.html

Composite Video Modification for the ZX81
http://www.breakintoprogram.co.uk/hardware/zx81-hardware/composite-video-modification-for-the-zx81

Adding composite video to a Sinclair ZX81
https://www.classic-computers.org.nz/blog/2016-01-03-composite-video-for-zx81.htm

ZX81 Hardare Hacking – Homebrew ZX8-CCB
https://www.evolutional.co.uk/post/zx81-homebrew-zx8ccb/

ZX81/TIMEX-SINCLAIR 1000 Composite Video Mod Part 2 – Plus Troubleshooting
https://blog.codesurfer.dev/zx81-composite-video-mod-part-ii/

ZX81CCP video output for ZX81
https://www.sinclairzxworld.com/viewtopic.php?t=840

TK85 A/V Reloaded – Saída de Vídeo Composto para o TK85
https://victortrucco.com/TK/TK85AVReloaded/TK85AVReloaded

ZX81 Video Signal
https://trastero.speccy.org/cosas/JL/ZX81-ULA/ZX81-video.html

ZX81 Video Conditioning Mods
https://www.evolutional.co.uk/post/zx81-video-conditioning-mods/

(ZX81) Composite mod voltages
https://www.sinclairzxworld.com/viewtopic.php?f=10&t=622

ZX81 video display system – A tutorial by wilf rigter – last revision 7 Sept 1996
https://8bit-museum.de/heimcomputer-2/sinclair/sinclair-scans/scans-zx81-video-display-system/

Video Signal ZX81 Old/New Version
https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=588&f=2&t=588

Wilf Rigter
https://timexsinclair.com/indiv/wilf-rigter/
http://web.archive.org/web/20201108114958/http://www.user.dccnet.com/wrigter/index_files/ZX%20Video%20Tutorial.htm

Circuitos de vídeo para el ZX81
https://trastero.speccy.org/cosas/JL/zx81%282%29/ZX81-video.html

• ZX81 back porch video mods:

Back Porch Tv Signal Generator
http://www.fruitcake.plus.com/Sinclair/ZX80/VideoGeneration/ZX80_BackPorchGeneration.htm

ZX81 Composite Video with Backporch
https://github.com/redhawk668/ZX81-Composite

ZX81 Composite PCB
https://www.bitwrangler.uk/2021/11/21/zx81-composite-pcb/

Saída de Vídeo Composto no ZX81
https://victortrucco.com/TK/ZX81Backporch/ZX81Backporch

**
Please check out my “8-bit Shack” retro computing channel
https://www.youtube.com/@8bit-shack

and my Tindie store.
https://www.tindie.com/stores/dtronixs/

Thanks

Advertisement

Building a Sinclair ZX81 PSU Lead

I had a ZX81 to test but no power supply or leads for it. So here some information on ZX81 power supplys and building a DIY power lead for the ZX81.

There were two ZX81 power supplies. The first was a UK700 which could provide a DC current of 700mA or 0.7A and the bigger UK1200 which could provide a DC current of 1200mA or 1.2A.

Pictures from https://popeymongames.co.uk

The ZX81 used a 3.5mm jack connector, this was a bit different to the more common 2.1mm DC barrel jack, but not that uncommon for the time.

So that means I going to build a power lead and to make a lead we have

• a 3.5mm mono jack plug,
• some red and black wire and
• a couple of banana plugs.

The 3.5mm jack connector has a tip and a sleeve

and for the ZX81 the tip was +9VDC and the sleeve was 0V.

Here’s my video building the power lead.

Building a Sinclair ZX81 DIY PSU Lead
https://www.youtube.com/watch?v=Yeu9cNu4X98

In addition I’ve put together some weblinks:

How Many Sinclair ZX81 Power Supplies Are There?
https://popeymongames.co.uk/2021/10/11/how-many-zx81-power-supplies-are-there/

Phone connector (audio)
https://en.wikipedia.org/wiki/Phone_connector_(audio)

ZX81 Repair Part 1. Power Supply
https://www.youtube.com/watch?v=CXPJPMD8bew

JoulesperCoulomb – ZX Spectrum Power Supplies
https://www.youtube.com/watch?v=qTRiS4isYGk

Power supplies of the 8 bit generation
http://blog.tynemouthsoftware.co.uk/2022/08/power-supplies-of-the-8-bit-generation.html

Please check out my “8-bit Shack” retro computing channel
https://www.youtube.com/@8bit-shack

and my Tindie store.
https://www.tindie.com/stores/dtronixs/

Dragon32 – Unboxing a 35-year old loft find

From my “8-bit Shack” retro computing channel

Dragon32 – Unboxing a 35-year old loft find

A rare beast of a Dragon 32 home computer. Found, lost in a loft for 35 or so years.

What will we find inside the box?
and will it still work after all these years?

websites

History
https://en.wikipedia.org/wiki/Dragon_32/64
https://de.wikipedia.org/wiki/Dragon_32,_Dragon_64
https://en.wikipedia.org/wiki/Dragon_Data
https://en.wikipedia.org/wiki/Mettoy

https://www.theregister.com/2012/08/01/the_dragon_32_is_30_years_old/
https://www.nostalgianerd.com/the-dragon-32/
https://archive.worldofdragon.org/index.php?title=Dragon_History
https://www.binarydinosaurs.co.uk/Museum/Dragon/dragon-history.php

Data
http://www.dragondata.co.uk/
http://archive.worldofdragon.org/index.php?title=Main_Page
http://www.archive.worldofdragon.org/index.php?title=Technical

Pin-outs

Power 9-Pin D
http://dragon32.info/info/psu.html

Video Monitor 5-pin DIN
http://dragon32.info/info/pinouts.html

Dragon Logo redrawn by Thomas Gutmeier from
http://www.8bit-homecomputermuseum.at/downloads/downloads.html

Please check out my “8-bit Shack” retro computing channel
https://www.youtube.com/@8bit-shack

and my Tindie store.
https://www.tindie.com/stores/dtronixs/

Thanks

Commodore C64 Rebuilds & Clones

Following on from my post about “Keeping your ZX Spectrum going” and other Spectrum posts here’s my first post for doing the same for the Commodore C64.

Diagnostic tools, replacement boards, PSU protectors, video improvements, cartridges

C64 Schematics
http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/index.html

Clones
https://github.com/KicadRetroArchive/Commodore64C
https://www.youtube.com/watch?v=TUZ7yFeUuvY
https://github.com/jgrip/open128/
https://www.uni64.com/en/p/atx64
https://www.uni64.com/en/p/64-tuning-board-v2
https://www.uni64.com/en/p/pulse64-alien-eliminator
https://c128.se/ C128 clone
https://github.com/jgrip/open128/ C128 clone
https://github.com/bwack/C64-250407-Replica-KiCad
https://diychris.com/index.php/commodore-64-replica-250407-04/

Alternatives to tapes and disc drives i.e as tapuino, pi1541

https://github.com/svenpetersen1965
https://github.com/boelle?tab=repositories
https://github.com/TMO2018
https://github.com/wagiminator/C64-Collection

https://github.com/StormTrooper/tapuinoCute32http://www.manosoft.it/

Tapes
https://github.com/KimJorgensen/tapecart
https://www.pcbway.com/project/shareproject/Tapecart_SD_is_a_Easy_to_Use_Commodore_64_SD_Card_Loader_.html
https://github.com/ttahsin-bey/TapeCart-PC-Adapter
https://github.com/arananet/Tapuino-Reloaded

pi1541
https://github.com/arananet/pi1541pcb
https://cbm-pi1541.firebaseapp.com/
https://github.com/tebl/C64-Pi1541-II
Pi1541 in 1541 Case & More (Bare Tapuino, Audio & Composite LCD power) – Part 1
https://hobbytronics.home.blog/2019/05/12/pi1541-in-1541-case-more-bare-tapuino-audio-composite-lcd-power-part-1/
Pi1541 in 1541 Case & Tapuino – Part 2 (Board Etching and Build)
https://hobbytronics.home.blog/2019/07/07/pi1541-in-1541-case-more-board-etching-and-build-part-2/
Pi1541 in 1541 Case & Tapuino – Part 3 : Schematics and a bit
https://hobbytronics.home.blog/2019/10/15/pi1541-in-1541-case-tapuino-part-3-schematics-and-a-bit/

Cartridges
https://github.com/SukkoPera/OpenC64Cart
https://github.com/KimJorgensen/KungFuFlash
Remaking Commodore 64 Cartridges
https://hobbytronics.home.blog/2020/12/06/remaking-commodore-64-cartridges/

Power Supplys

C64-replacement-PSU-230VAC
https://github.com/svenpetersen1965/C64-replacement-PSU-230VAC-

C64-PSU-Global
https://github.com/svenpetersen1965/C64-PSU-Global

Bwack’s C64 saver designs.
https://github.com/bwack/C64-Saver-bwack

Building a new C64 Power Supply
https://janbeta.net/c64-power-supply/
https://www.youtube.com/watch?v=IpuKz0TTB2I

Building a DIY C64 Power Supply (The Lazy Way)
https://www.youtube.com/watch?v=wWOU2sZv_ng

GWB#1 – Commodore 64 / 1541-II PSU
http://greisisworkbench.blogspot.com/2017/03/hi-here-is-my-design-for-c64-and-1541.html
https://www.youtube.com/watch?v=oY6ycn7qmzo

Video
https://github.com/Jaystonian/ClearVideo
https://retrotinkerer.wordpress.com/2018/07/11/poors-man-c64-s-video-mod/

PLA/PAL
https://github.com/desaster/c64-dodgypla
https://github.com/Jaystonian/C64-250469-SuperPLA
https://github.com/CrackenDesigns/PLASGEN

Repairs
C64
https://www.youtube.com/watch?v=eEDCsCpShtY
https://www.youtube.com/channel/UCE5dIscvDxrb7CD5uiJJOiw
https://retrocomputerverzamelaar.nl/commodore-64-problems/

1541
https://www.youtube.com/watch?v=Gl_WRg6jDR8
https://www.youtube.com/watch?v=yAIMBAZaL6E
https://www.youtube.com/watch?v=EfL9Yv0wZg4
https://www.youtube.com/watch?v=FBmBzirEgCY
https://www.youtube.com/watch?v=-gDKl15WYuc
https://www.youtube.com/watch?v=FBmBzirEgCY

Chips
https://github.com/DL2DW/EasyGate1541-II

Please check out my “8-bit Shack” retro computing channel

and my Tindie store.

Thanks

Dragon32 PSU Testing

This is my first repair videos. Its testing a Dragon 32 PSU from a 35-year old loft find.

Dragon 32 (from Wikipedia)
https://en.wikipedia.org/wiki/Dragon_32/64

Dragon 32 Power 9-Pin D Pin-outs
http://dragon32.info/info/psu.html

“8-bit Shack” my retro computing YouTube channel

Whilst I’ve been writing this blog for over 10-years I’ve never found time to document the many retro computer repairs and their modifications I’ve done during this time. Which I feel is a big neglect on my behalf.

So in an effort to address this I’ve started a Youtube channel called the “8-bit Shack” where I hope to share videos of any future computer repairs and modifications.

On the “8-bit Shack” channel you will find videos of retro computer repairs, teardowns, modifications, reviews and also a little retro computing history along the way as well.

If you like any of these things, please consider leaving a comment or feedback either here or on my Youtube channel or even becoming a subscribing to the “8-bit Shack” retro computing channel.

Thank You.

Replacement ZX Spectrum ULA’s

Following on from my post about “Replacement ZX81 ULA’s” I thought I would look at the ZX Spectrum ULA.

If you want a excellent technical archology on the ZX Spectrum and its ULA check out Chris Smith’s “The ZX Spectrum ULA – How to design a Microcomputer”. It is a masterclass in technical forensics on the ZX Spectrum ULA.

Technical Background:

ZX Spectrum ULA Types
https://spectrumforeveryone.com/technical/zx-spectrum-ula-types/

ZX Spectrum 48K ULA differences
https://www.bytedelight.com/?p=41

ZX Spectrum and ZX81 ULA gallery
https://www.bytedelight.com/?page_id=2678

Yellow screen
https://spectrumcomputing.co.uk/forums/viewtopic.php?p=71331#p71331

Replacement ULA’s:

ZX Spectrum 16/48K:

Nebula (16/48K)
https://www.retroleum.co.uk/zx-spectrum-chips

SLAM ULA (versions for 48K and 128K): get one on SellMyRetro

VLA82 (16/48K)
https://vdrivezx.com/vLA82

ZX Spectrum 128K:

SLAM ULA (versions for 48K and 128K)
get one on SellMyRetro

vLA128
https://vdrivezx.com/vla128/

Please check out “8-Bit Shack” my retro computing youtube channel.

Finally, if you know of any other websites with ZX Spectrum ULA information please leave a comment.
Check out my Tindie store.

Replacement ZX81 ULA’s

One of the most difficult things about servicing and repairing retro computers is finding parts. Early computers would use standard logic chips such as 74 TTL or 74LS TTL or 4000 CMOS but in a drive to make cheaper computers most computer manufacturers would eventually use custom chips to get component costs down. “Classic” Standard logic is still available(-ish) but custom chips are not. To fill this need, many ingenuous makers have spent time and effort to design alternative and replacement custom chips using more modern FPGA chip technology.

The Sinclair ZX81 was one of the first computers to use a custom chip to keep its cost down. It the case of a Uncomitted Logic Array (ULA) chip from Ferranti and later from other manufacturers.

This allowed Sinclair to reduce the ZX81 selling price to £69.95 from the previous selling price of £99.95 for the Sinclair ZX80. This was achieved by reducing the chip count from 21 chips for the ZX80 to 4 chips for the ZX81.

Technical Background:

ZX81 ULA
https://www.sinclairzxworld.com/viewtopic.php?f=8&t=2928

Query on a Issue 1 ZX81
https://www.sinclairzxworld.com/viewtopic.php?f=7&t=1387

ZX81 ULA-in-a-CPLD
https://www.sinclairzxworld.com/viewtopic.php?f=6&t=871

Sinclair SCL/ULA
https://www.sinclairzxworld.com/viewtopic.php?f=7&t=4853

Exploring the Timex/Sinclair 1000’s Sinclair Logic Chip (SCL)
https://www.sinclairzxworld.com/viewtopic.php?p=48485#p48485

ZX81 Versions/Issues
https://www.sinclairzxworld.com/viewtopic.php?f=7&t=762

ZX Spectrum and ZX81 ULA gallery
https://www.bytedelight.com/?page_id=2678

ZX81 ULA Replacement.
https://oldcomputer.info/8bit/zx81/ULA/ula.htm

Houston, we have an image!
https://sinclairzxworld.com/viewtopic.php?t=653

Replacement ULA’s

VLa81
https://vdrivezx.com/vla81/

zx81ula-vhdl
https://github.com/jjmz/ula-vhdl

ZX81 Bodo Wenzel ULA
https://trastero.speccy.org/cosas/JL/ZX81-ULA/ZX81-ULA.html

New Old Stock (NOS)

BRAND NEW ZX81 2C210E ULA with Heatsink @ £49.95
https://www.mutant-caterpillar.co.uk/shop/product_info.php?products_id=2901

If you know of any other websites with ZX81 ULA information please leave a comment.

Please check out “8-Bit Shack” my retro computing youtube channel.

Check out my Tindie store.

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ZX81 Mods and Repairs

Some more links for your retro computer repairs, this time for the Sinclair ZX81:

ZX81 Motherboard
http://www.breakintoprogram.co.uk/hardware/computers/zx81/hardware

Fixing a poorly ZX81
http://www.breakintoprogram.co.uk/hardware/fixing-a-poorly-zx81

ZX81 Video Conditioning
https://www.youtube.com/watch?v=1irH3KuGyl0

ZX80/ZX81/TS1000 composite video mods
https://www.bytedelight.com/?page_id=3560

Le Sinclair ZX81
http://fetrmartin.free.fr/ZX81/

Timex Sinclair 1000 Part 1: Multi Region Composite Mod
https://hobbytronics.home.blog/2019/12/15/timex-sinclair-1000-part-1-multi-region-composite-mod/

ZX81/TIMEX-SINCLAIR 1000 Composite Video Mod Part
https://blog.codesurfer.dev/zx81-timex-sinclair-1000-composite-video-mod/

ZX81/TIMEX-SINCLAIR 1000 Composite Video Mod Part 2 – Plus Troubleshooting
https://blog.codesurfer.dev/zx81-composite-video-mod-part-ii/

Sinclair ZX81 Repair & Composite Mod
https://www.youtube.com/watch?v=5OQuJ-GMwF4

vLA81 – A ZX81 ULA replacement
https://vdrivezx.com/vla81/

Timex Sinclair 1000 Part 1: Multi Region Composite Mod
https://hobbytronics.home.blog/2019/12/15/timex-sinclair-1000-part-1-multi-region-composite-mod/
Timex Sinclair 1000 Part 2: Recap and 16k Internal Ram
https://hobbytronics.home.blog/2019/12/16/timex-sinclair-1000-part-2-recap-and-16k-internal-ram/

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C64 SD2IEC & Tapuino

SD2IEC is a very popular SD-Card loading interface of the Commodore C64 computer. It has been evolved, been reimaged and reworked over the years. Teaming it up with a fast loader such as EPYX makes a great combo.

So here’s a list of some of those boards:

sd2iec file dump
https://www.sd2iec.de/
C64 SD2IEC SW SMD

https://oshwlab.com/wagiminator/y-c64-sd2iec-smd

SD2IEC – C64 SD Card Adapter
https://oshwlab.com/wagiminator/y-c64-sd2iec-smd_copy

Commodore C64 Collection
https://github.com/wagiminator/C64-Collection

SD2iEC & EPYX FAST LOAD
https://www.pcbway.com/project/shareproject/_DIY__SD2iEC___EPYX_FAST_LOAD_CARTRIDGE_FOR_COMMODORE_64.html

Epyx Fast Load
https://en.wikipedia.org/wiki/Epyx_Fast_Load

FreeLoad
http://www.sys64738.net/ddifl/ddifl.htm

Designer Stefan Wagner has been busy over the years and has his latest offerings:

Tapuino – Commodore Datasette Emulator based on ATmega328P
https://hackaday.io/project/186894-tapuino

TapeDump64 – Simple Commodore Datasette to USB Adapter based on ATtiny412
https://hackaday.io/project/186237-tapedump64

TapeBuddy64 – Advanced Commodore Datasette to USB Adapter based on ATtiny814
https://hackaday.io/project/186238-tapebuddy64

DiskBuddy64 – Commodore Floppy Disk Drive to USB Adapter based on ATtiny412
https://hackaday.io/project/186239-diskbuddy64