ZX81 Repair

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ZX81 Repair

Postby Jman on Sun Jan 17, 2016 2:27 pm

Hi

I thought I would share my experience in getting a ZX81 going
I purchased an untested ZX81 with 16K ram expansion module
When I eventually got around to testing it I soon discovered the untested unit
was in fact faulty. No or extremely weak video was the issue and this meant a
new ULA was required the original ULA was a 2C184E (1st gen i believe) as these are no longer
available a 2C210E was ordered. Once this was fitted the ZX81 was back in action
not having a CRT TV i decided to fit a ZX8CCB at the same time. The picture quality
on my Sony LCD is surprisingly good with this mod. Of course it never ends there.
The keyboard membrane had a crack in the normal spot (under the ram chip).
I know new membranes can be purchased but this meant more delays and more $$.
The pictures show how i fixed this problem and the cool raised keyboard that came with the machine.
First remove the Molex connectors from the PCB then make 2 extensions using ribbon cable
and cut a 16 pin IC socket cut to size(8 pins and 5 pins). Cut the membrane below the crack and fit to the original
connectors these then plug into the IC sockets making removal a lot safer next time.

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Regards
Jman
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Re: ZX81 Repair

Postby tezza on Mon Jan 25, 2016 2:10 pm

Good stuff! Interesting to read about the membrane fix. Thanks for posting.
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Re: ZX81 Repair

Postby kevman3d on Sun Jan 31, 2016 10:35 am

tezza wrote:Good stuff! Interesting to read about the membrane fix. Thanks for posting.

Ditto. Nice post! Good solution! Didn't think about doing that... :)

I ordered a new membrane - though I decided to try remove it in anticipation I might have needed one anyway. Not quite as easy as it seemed, and it split the layers so the top/bottom were loose and separated - so I had no choice anyway...

Also have the ZX8CCB - that (and the membrane) is the project for today or tomorrow since its a long weekend. However given the heat here, its hard to be motivated to do anything when its almost 30 degrees inside the house... That might be left a few more weeks, but we'll see if things cool down later in the day. :roll:

Jman wrote:available a 2C210E was ordered.


Does anybody know where to get small heatsinks btw? Its not such a bad idea to dissipate some of that ULA heat... I guess you ordered that from mutant-caterpillar? I know they mention that they attach heatsinks (according to their site).

That said, it never needed one originally - but I'm talking a couple of decades ago, and the chip was a little "newer" back then... :D

I have one of those plastic keyboards - but I never really used it back in the day as it got so frustrating to use (heavier press needed, and sometimes the keys would slip inside and stick, etc) I ended up removing it. But we're talking 25+ years ago now. lol! :lol:
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