Introduce yourself to your fellow forum members - what was your journey into the Sinclair world?
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Gary C
Posts: 1
Joined: Tue Jun 05, 2018 9:22 pm


Post by Gary C » Sun Jun 24, 2018 3:34 pm

Hi everyone.
Just getting back into 80's computers and trying to put together a collection of the machines I wanted at the time.

Had one of the first zx81's back in the day but gave it away many years ago. I then ended up working in a nuclear power station, writing reactor control software in CUTLASS and maintaining Honeywell DPS 6 supermini's and 8086/80286 target control computers. The amazing thing is, they are all still there and working !

Have a issue 1 zx81 needing repair, so may ask for some help. ULA is giving a clock signal and a blank video signal, but the processor isn't running :)

Also got

BBC B (fully working)
Spectrum (now fixed)
Apple ii eruoplus with z80 second processor (in need of tlc)
TRS80 series 4 (currently on shelf at work where it's been for 35 years, in process of being liberated)
3032 commodore PET (fully working, case needs a spray job)

RM-380Z (pipe dream ?)
Memotech MTX-512

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Andy Rea
Posts: 1530
Joined: Fri May 09, 2008 2:48 pm
Location: notts UK

Re: Hello

Post by Andy Rea » Sun Jun 24, 2018 8:36 pm

Hello Gary C,

welcome to our crazy club... bear in mind some of us are crazy also :lol: anyway you've come to the right place for some help with the hunble 81.

you say the ULA is giving a clock signal but is it getting to the cpu? check pin 6 at the cpu, it is an inverted signal from the ula , been inverted by tr2.

regards Andy
6 x ZX81, 1 x TS1500 , 1 x +3e, 1 x timex 2040 printer, 1 x timex 2020 cassette deck, siclair printer and some spectrum

Posts: 241
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: Hello

Post by McKlaud » Sun Jun 24, 2018 10:58 pm

Hi Garry C.

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Posts: 367
Joined: Tue Nov 01, 2011 12:16 am
Location: Hengelo, NL

Re: Hello

Post by RetroTechie » Wed Jun 27, 2018 7:08 pm

Welcome, Garry! ;)

For fixing your ZX81, what tools you have available? Scope or even a simple logic probe would be very helpful. Any other ZX81's in your possession that you could swap parts with?

Usually ZX81's are easy to fix, with 2 exceptions:
  • ULA itself. If that's dead (or its video output blown), there isn't much you can do. Some modern ULA replacements are out there, though.
  • Keyboard. But you can buy replacement keyboard foils. And some die-hards like on here have built their own keyboard for the Zeddy.
In other words like a classic car: if you want it enough, it CAN be fixed. :D

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Posts: 2330
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Hello

Post by 1024MAK » Thu Jun 28, 2018 8:53 pm

Hello Gary

Welcome to our forum :D

Please take a look around. There are gems of information everywhere. And if you have a question, please ask.


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