ZX81 rebuild

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

Re: ZX81 rebuild

Post by Lardo Boffin »

Diodes and transistors.

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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 »

Some big bits added.

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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 »

Switched it on and sadly nothing. Well, nearly - after a couple of seconds i get a brief flash of white and then it goes black again. :cry: :cry: The time delay between switch on and flash and death roughly corresponds to how long it takes to work out that it has 16k of RAM.

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Now - where do I start with sorting this out? :?: A beer and then bed I think. Worry about it tomorrow.
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
sirmorris
Posts: 2811
Joined: Thu May 08, 2008 5:45 pm

Re: ZX81 rebuild

Post by sirmorris »

Maybe an address line stuck? All fine until you hit a certain place in the program?
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin »

Thanks sirmorris. Although not sure how to test that...

I need to make sure the ZX8-CCB is correctly tuned. Although it works fine / reasonably on all the zeddies i have tried it with.

My plan is to double check what i ordered and how I labelled the bags and then triple check the soldering and for shorts. After that it is :?: time!

Lardo
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 got the 6.5mhz resonator from sell my retro:-

https://www.sellmyretro.com/offer/detai ... ck%29-3469

What is the correct alignment for this? Does it matter? I went with the same as an installed one (lettering facing the ULA). The zeddy assembly guide doesn’t specify a way round, unless I missed it?
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
sirmorris
Posts: 2811
Joined: Thu May 08, 2008 5:45 pm

Re: ZX81 rebuild

Post by sirmorris »

It's not polarised, any way is fine.
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK »

sirmorris wrote: Sat Nov 18, 2017 5:50 pm It's not polarised, any way is fine.
Except upside down :lol:

If you have a 'scope or logic probe, check Z80 address lines A14 and A15.
Also is you have a 'scope, test the video/TV output pin to see if it is switching between the three levels (high = white, "mid-way" = black and low= low part of the sync pulses).

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

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Andy Rea
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Re: ZX81 rebuild

Post by Andy Rea »

I would check for shorts near the data pins of the cpu, the track clearances are quite close around there, also the diodes near the keyboard connector some.of the traces run very close to the diode pads.

Other than it not working it looks very nice, good job so far.

Regards Andy
what's that Smell.... smells like fresh flux and solder fumes...
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 rebuild

Post by Lardo Boffin »

1024MAK wrote: Sat Nov 18, 2017 6:55 pm
sirmorris wrote: Sat Nov 18, 2017 5:50 pm It's not polarised, any way is fine.
Except upside down :lol:

If you have a 'scope or logic probe, check Z80 address lines A14 and A15.
Also is you have a 'scope, test the video/TV output pin to see if it is switching between the three levels (high = white, "mid-way" = black and low= low part of the sync pulses).

Mark
I managed not to go for the Australia fit...

I don't have a scope or probe. I never really intended getting this involved with hardware - it just kind of happened! Things have certainly moved on from ‘can I fit a ZX8-CCB?’ :o Is there a reasonably priced probe i can get? I don’t want to spend loads as it probably won’t get a huge amount of usage.
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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