ZX81 ULA

ZX80 / ZX81 hardware and software offered for sale or swapping
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mrtinb
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Joined: Fri Nov 06, 2015 5:44 pm
Location: Denmark
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Re: ZX81 ULA

Post by mrtinb » Tue Jul 03, 2018 9:22 pm

Mine arrived today.

The ULA was for repair of my first ZX81 imported from the Danish company ZXdata.

I have had it working and shortly after joining this forum it broke with white screen. The conclusion back them was the ULA must be broken. I had a digital probe to test with. Since then I used a lot of energy to desolder the ULA and finally broke it to pieces to get it off. For a novice it's impossible to remove an IC without a desolder gun.

So tonight I repaired the PCB which had been damaged in the ULA removal process. And added the 1K resistor and ground to the ULA to get it working through the modulator.

Unfortunately it's an unstable gray screen so something has changed. Debugging will continue when I receive my cheap oscilloscope from China.

Image
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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

Re: ZX81 ULA

Post by Andy Rea » Tue Jul 03, 2018 9:33 pm

Hi Martin,

A little late now but the easiest and safest way to remove a DIP IC is to cut all the pins with a fine pair of side cutters and then remove each pin one by one using soldering iron and tweezers, then with plenty of flux and some desolder braid removes solder form holes ( you may need to flip board and go from both sides) do not dwell too long n any single hole, if difficult move on and allow that area to cool a little and return later, sometimes more flus and fresh solder can also help.

anyway i really hope you fitted a socket and didn't solder te module in directly :|

i would first get a multi meter and check continuity from all the pins of the ULS to the respective parts of the circuit

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

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

Re: ZX81 ULA

Post by Andy Rea » Tue Jul 03, 2018 11:12 pm

on your marks....

get set...

GO...

to Link in first post 8 more up for grabs.


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: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 ULA

Post by Lardo Boffin » Wed Jul 04, 2018 8:55 am

Argh! Missed out again! These things go faster than hot cakes.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

roganjosh
Posts: 8
Joined: Thu Jun 14, 2018 12:59 pm

Re: ZX81 ULA

Post by roganjosh » Wed Jul 04, 2018 9:23 am

Lardo Boffin wrote:
Wed Jul 04, 2018 8:55 am
Argh! Missed out again! These things go faster than hot cakes.
If it's any consolation I was looking at the sellmyretro entry last night and this morning. From the 8 made available there were still four left when I hit the sack and at 06.00 today there were still two. So at least you've not got much competition from people across the pond.

Under circumstances of limited supply "Mine arrived today" posts might not do much to improve your mood, though I prefer to think that it's just elation rather than an attempt to make you paranoid.

Alan

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 ULA

Post by Lardo Boffin » Wed Jul 04, 2018 10:59 am

roganjosh wrote:
Wed Jul 04, 2018 9:23 am
Lardo Boffin wrote:
Wed Jul 04, 2018 8:55 am
Argh! Missed out again! These things go faster than hot cakes.
If it's any consolation I was looking at the sellmyretro entry last night and this morning. From the 8 made available there were still four left when I hit the sack and at 06.00 today there were still two. So at least you've not got much competition from people across the pond.

Under circumstances of limited supply "Mine arrived today" posts might not do much to improve your mood, though I prefer to think that it's just elation rather than an attempt to make you paranoid.

Alan
I’m not paranoid. They are out to get me. :? :D
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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1024MAK
Posts: 2539
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 ULA

Post by 1024MAK » Wed Jul 04, 2018 3:51 pm

I only posted details of mine's arrival so members could see how quick Andy is at posting them out Image

Mark

Moggy
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Joined: Wed Jun 18, 2008 2:00 pm

Re: ZX81 ULA

Post by Moggy » Wed Jul 04, 2018 4:51 pm

I wouldn't worry too much, Knowing Andy as I do I predict he won't stop till we all have at least one each and kudos to him for giving up the most important thing there is,that's his time and considering he's hand assembling the buggers himself it must be lengthy.

Lardo Boffin
Posts: 1073
Joined: Sat Nov 26, 2016 2:42 am

Re: ZX81 ULA

Post by Lardo Boffin » Wed Jul 04, 2018 7:27 pm

Moggy wrote:
Wed Jul 04, 2018 4:51 pm
I wouldn't worry too much, Knowing Andy as I do I predict he won't stop till we all have at least one each and kudos to him for giving up the most important thing there is,that's his time and considering he's hand assembling the buggers himself it must be lengthy.
Absolutely and well said.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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RetroTechie
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Location: Hengelo, NL
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Re: ZX81 ULA

Post by RetroTechie » Thu Jul 05, 2018 9:22 pm

mrtinb wrote:
Tue Jul 03, 2018 9:22 pm
For a novice it's impossible to remove an IC without a desolder gun.
Nope. Practice! Plain iron & solder pump go a long way. I rarely damage IC OR board. But it really takes practice to remove IC's without damaging a board. If that practice is lacking, safest method is to cut pins (and take destroyed IC as the cost of doing business ;) ).

And with the right tools & procedures, you can do this kind of thing a loooottt faster.

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