ZX81 rebuild

Discussions about Sinclair ZX80 and ZX81 Hardware
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Lardo Boffin
Posts: 662
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Fri Nov 17, 2017 9:54 pm

Diodes and transistors.

503CDB09-BE8B-4092-8263-1CFE73108DBB.jpeg
503CDB09-BE8B-4092-8263-1CFE73108DBB.jpeg (952.42 KiB) Viewed 187 times
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 662
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Fri Nov 17, 2017 10:31 pm

Some big bits added.

93A0A507-6923-4E83-B1B4-BA50DA8EB61B.jpeg
93A0A507-6923-4E83-B1B4-BA50DA8EB61B.jpeg (935.92 KiB) Viewed 176 times
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 662
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Fri Nov 17, 2017 10:41 pm

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.

0D32F08F-AEC4-47F5-B9C6-BDB555D07956.jpeg
0D32F08F-AEC4-47F5-B9C6-BDB555D07956.jpeg (896.11 KiB) Viewed 170 times

Now - where do I start with sorting this out? :?: A beer and then bed I think. Worry about it tomorrow.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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sirmorris
Posts: 2699
Joined: Thu May 08, 2008 4:45 pm
Location: oxon, uk

Re: ZX81 rebuild

Post by sirmorris » Sat Nov 18, 2017 12:03 pm

Maybe an address line stuck? All fine until you hit a certain place in the program?
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

Lardo Boffin
Posts: 662
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Sat Nov 18, 2017 12:50 pm

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
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 662
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Sat Nov 18, 2017 4:42 pm

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?
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

User avatar
sirmorris
Posts: 2699
Joined: Thu May 08, 2008 4:45 pm
Location: oxon, uk

Re: ZX81 rebuild

Post by sirmorris » Sat Nov 18, 2017 4:50 pm

It's not polarised, any way is fine.
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

User avatar
1024MAK
Posts: 1804
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 rebuild

Post by 1024MAK » Sat Nov 18, 2017 5:55 pm

sirmorris wrote:
Sat Nov 18, 2017 4:50 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

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Andy Rea
Posts: 1268
Joined: Fri May 09, 2008 1:48 pm
Location: notts UK

Re: ZX81 rebuild

Post by Andy Rea » Sat Nov 18, 2017 6:39 pm

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
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

Lardo Boffin
Posts: 662
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 rebuild

Post by Lardo Boffin » Sat Nov 18, 2017 6:40 pm

1024MAK wrote:
Sat Nov 18, 2017 5:55 pm
sirmorris wrote:
Sat Nov 18, 2017 4:50 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.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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