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Re: ZX81 ULA

Posted: Tue Jul 03, 2018 9:22 pm
by mrtinb
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

Re: ZX81 ULA

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

Re: ZX81 ULA

Posted: Tue Jul 03, 2018 11:12 pm
by Andy Rea
on your marks....

get set...

GO...

to Link in first post 8 more up for grabs.


Andy

Re: ZX81 ULA

Posted: Wed Jul 04, 2018 8:55 am
by Lardo Boffin
Argh! Missed out again! These things go faster than hot cakes.

Re: ZX81 ULA

Posted: Wed Jul 04, 2018 9:23 am
by roganjosh
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

Re: ZX81 ULA

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

Re: ZX81 ULA

Posted: Wed Jul 04, 2018 3:51 pm
by 1024MAK
I only posted details of mine's arrival so members could see how quick Andy is at posting them out Image

Mark

Re: ZX81 ULA

Posted: Wed Jul 04, 2018 4:51 pm
by Moggy
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.

Re: ZX81 ULA

Posted: Wed Jul 04, 2018 7:27 pm
by Lardo Boffin
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.

Re: ZX81 ULA

Posted: Thu Jul 05, 2018 9:22 pm
by RetroTechie
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.