"Different" ZX81's

Discussions about Sinclair ZX80 and ZX81 Hardware
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mrtinb
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Re: "Different" ZX81's

Post by mrtinb » Sat May 27, 2017 12:43 pm

Fwapp wrote:
Sat May 27, 2017 10:42 am
Wooo - nice!! The kludge fix ones are really nice to have in a collection. It amazes me that they could fix a software bug in the ROM by plonking hardware on the CPU - amazingly clever (at least from my point of view!)
That sounds interesting. Any description / explanation of it somewhere?
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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Fwapp
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Re: "Different" ZX81's

Post by Fwapp » Sat May 27, 2017 1:04 pm

mrtinb wrote:
Sat May 27, 2017 12:43 pm
Fwapp wrote:
Sat May 27, 2017 10:42 am
Wooo - nice!! The kludge fix ones are really nice to have in a collection. It amazes me that they could fix a software bug in the ROM by plonking hardware on the CPU - amazingly clever (at least from my point of view!)
That sounds interesting. Any description / explanation of it somewhere?
There's a good discussion here :) viewtopic.php?f=7&t=95&start=10
ZX80, ZX81 - 2C158C Bugged Rom iss.1, 2C158C "kludge fix" iss1, 2C184E iss1, 2C210E iss3, US NTSC iss1 "straight traces", US NTSC iss3 TS1000

Moggy
Posts: 1514
Joined: Wed Jun 18, 2008 1:00 pm

Re: "Different" ZX81's

Post by Moggy » Sat May 27, 2017 1:10 pm

Fwapp wrote:
Sat May 27, 2017 1:04 pm
mrtinb wrote:
Sat May 27, 2017 12:43 pm
Fwapp wrote:
Sat May 27, 2017 10:42 am
Wooo - nice!! The kludge fix ones are really nice to have in a collection. It amazes me that they could fix a software bug in the ROM by plonking hardware on the CPU - amazingly clever (at least from my point of view!)
That sounds interesting. Any description / explanation of it somewhere?
There's a good discussion here :) viewtopic.php?f=7&t=95&start=10


OOO thanks for finding that Mr Wappy I was about to dig that one up,seen the PM by the way very interesting and will be replying. :D

A little bit of info here as well.
http://www.binarydinosaurs.co.uk/museum ... /index.php

Lardo Boffin
Posts: 664
Joined: Sat Nov 26, 2016 1:42 am

Re: "Different" ZX81's

Post by Lardo Boffin » Sun May 28, 2017 10:35 am

mrtinb wrote:
Sat May 27, 2017 12:43 pm
Fwapp wrote:
Sat May 27, 2017 10:42 am
Wooo - nice!! The kludge fix ones are really nice to have in a collection. It amazes me that they could fix a software bug in the ROM by plonking hardware on the CPU - amazingly clever (at least from my point of view!)
That sounds interesting. Any description / explanation of it somewhere?
If you are looking to get one they are obviously the early ones so look out for ZX80 power supplies, UK700 supplies, larger spongy feet rather than the newer small and more solid ones. They also sometimes have different cassette cables. If you get the angle of the photo right you can see the extra board sat on top of the ROM from outside.

Assuming you don't know all that already of course!

I don't have any photos to hand but can add some later.

I've bought nearly 15 zeddys so far (many have been composite modded and sold on) and ended up with a kludge fix as well as a still bugged one! Patience may be required....

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
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Joined: Sat Nov 26, 2016 1:42 am

Re: "Different" ZX81's

Post by Lardo Boffin » Fri Jun 09, 2017 2:32 pm

Well I just bought two more zeddys and guess what? One of them is a kludge fix! And appears to be working nicely as well!
IMG_6077.JPG
IMG_6077.JPG (2.53 MiB) Viewed 246 times
There I was saying they were fairly rare!

I was going to refurb these and stick them both back on eBay (profit goes to Cancer Research) but if anyone is looking for a kludge fix let me known via PM and I will happily pass it on for cost plus p&p to a forumite. After some more thorough testing of course.

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

Moggy
Posts: 1514
Joined: Wed Jun 18, 2008 1:00 pm

Re: "Different" ZX81's

Post by Moggy » Fri Jun 09, 2017 4:27 pm

Hells teeth Lardo are you buying the whole bloody stock of UK zeddies!? :lol:

Seriously though a cracking example there and total kudos for the Cancer Research donation nice one sir. :D

Lardo Boffin
Posts: 664
Joined: Sat Nov 26, 2016 1:42 am

Re: "Different" ZX81's

Post by Lardo Boffin » Fri Jun 09, 2017 4:46 pm

Moggy wrote:
Fri Jun 09, 2017 4:27 pm
Hells teeth Lardo are you buying the whole bloody stock of UK zeddies!? :lol:

Seriously though a cracking example there and total kudos for the Cancer Research donation nice one sir. :D
If I'm being honest I enjoy the process of buying them, refurbing them and then selling (or trying to) them for a few extra quid. This specific charity thing is relatively recent after someone I knew succumbed to 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

Moggy
Posts: 1514
Joined: Wed Jun 18, 2008 1:00 pm

Re: "Different" ZX81's

Post by Moggy » Fri Jun 09, 2017 4:53 pm

Understood Lardo, they seem to be at just the right amount of complexity to have a mess around as opposed to say a pc motherboard.

Lardo Boffin
Posts: 664
Joined: Sat Nov 26, 2016 1:42 am

Re: "Different" ZX81's

Post by Lardo Boffin » Fri Jun 16, 2017 10:33 am

So I bought a cheap zeddy as a ULA donor recently and luckily it was socketed and working. It also has a nice aftermarket modification going on...

IMG_6151.JPG
IMG_6151.JPG (2.06 MiB) Viewed 193 times

Apparently it was connected to a battery when the previous owner took it to their caravan. Now there is dedication to the cause!

It's also nice to see someone who's soldering was messier than mine! :D

IMG_6152.JPG
IMG_6152.JPG (2.43 MiB) Viewed 193 times

Not sure about the regulator though - looks a bit broken.

I have not tried to see if it works as I didn't want to risk it killing the ULA. When I have a new one from the 5 Euro ULA thread I will give it a go.

May remove the battery mod first though...

As an aside would I just need to connect it to a 9V battery to make it go (assuming it works of course)? Would be nice to have a zeddy laptop! :lol:

Oh and another nice clean board! The edge connectors look unused.

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

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1024MAK
Posts: 1805
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: "Different" ZX81's

Post by 1024MAK » Fri Jun 16, 2017 12:39 pm

If as I suspect, the 7805 voltage regulator has a chunk missing out of the middle of the plastic case, then it has been seriously abused :evil:
Given that they can take a wide input voltage range, it's most likely due to reverse voltage (incorrect input polarity) damage :(

Oh, and any Zeddy on it's own can operate from a regulated or battery supply of 7.5V to 12V DC. If a switching DC/DC converter/regulator is fitted (or a larger heatsink to the 7805) it can run from even higher voltage DC supplies.

Mark

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