UK Vintage Radio Repair and Restoration Discussion Forum

UK Vintage Radio Repair and Restoration Discussion Forum (https://www.vintage-radio.net/forum/index.php)
-   Vintage Computers (https://www.vintage-radio.net/forum/forumdisplay.php?f=16)
-   -   Zx81 (https://www.vintage-radio.net/forum/showthread.php?t=164648)

julie_m 4th May 2020 3:59 pm

Re: Zx81
 
The ZX81 keyboard was never very highly regarded as a keyboard, and one of the most popular upgrades was a "proper" keyboard.

You can easily build something better with tactile switches and copper-strip breadboard.

The ZX cursor keys are 5, 6, 7, 8, 0 (in the same order, left-down-up-right as vi) not 6, 7, 8, 9, 0, and therefore span two half-rows of the matrix. But you should be able to use 4016 / 4066 bilateral switches to simulate keystrokes.

SiriusHardware 4th May 2020 4:12 pm

Re: Zx81
 
I stand corrected - I was thinking in any case that by indulging in my usual fetish for optocouplers, the stick could turn on the five opto leds fed from a common supply and through a common return, and the opto outputs could be across any key / row intersection desired, no matter whereabouts in the row / column matrix they might be. Add a bit of switching and you can 'set' the output matrix to match the keys used on a few different games.

I can't remember if the '81 ever came to have a de facto standard joystick, in the way that the 'Kempston' became one of two standards - the other being the Interface 2 standard - on the Spectrum.

My 'Other' ZX81, the one which is suffering from weak UHF output, is in a full sized third party 'Dktronics' enclosure / keyboard - in fact I 'rescued' it from a fellow forum member precisely because it had that rather uncommon form factor. It's in really nice condition as well.

The modern replica replacement keyboard membranes are apparently a lot better than the originals, in so far as any membrane keypad can ever be good, of course.

John Earland 5th May 2020 8:38 am

Re: Zx81
 
Quote:

Originally Posted by SiriusHardware (Post 1242629)
I stand corrected - I was thinking in any case that by indulging in my usual fetish for optocouplers, the stick could turn on the five opto leds fed from a common supply and through a common return, and the opto outputs could be across any key / row intersection desired, no matter whereabouts in the row / column matrix they might be. Add a bit of switching and you can 'set' the output matrix to match the keys used on a few different games.

I can't remember if the '81 ever came to have a de facto standard joystick, in the way that the 'Kempston' became one of two standards - the other being the Interface 2 standard - on the Spectrum.

My 'Other' ZX81, the one which is suffering from weak UHF output, is in a full sized third party 'Dktronics' enclosure / keyboard - in fact I 'rescued' it from a fellow forum member precisely because it had that rather uncommon form factor. It's in really nice condition as well.

The modern replica replacement keyboard membranes are apparently a lot better than the originals, in so far as any membrane keypad can ever be good, of course.

I have one of those replica keyboards and they are very responsive.

SiriusHardware 5th May 2020 7:45 pm

Re: Zx81
 
The replacement arrived today, but when I peeled off the original membrane all of the incredibly sticky backing remained on the casing instead of coming off with the old membrane as I rather hoped it would.

I don't want the new membrane to get off to a bumpy start, so I'm going to have to have a think about how to get the old sticky stuff off. IPA barely makes a dent in it. What did you do?

John Earland 5th May 2020 7:59 pm

Re: Zx81
 
Quote:

Originally Posted by SiriusHardware (Post 1243094)
The replacement arrived today, but when I peeled off the original membrane all of the incredibly sticky backing remained on the casing instead of coming off with the old membrane as I rather hoped it would.

I don't want the new membrane to get off to a bumpy start, so I'm going to have to have a think about how to get the old sticky stuff off. IPA barely makes a dent in it. What did you do?

I was really lucky-most of the glue came off with with membrane. The bits that did stubbornly remain I rubbed with my fingers, pushing them until they rolled into little balls of glue and then I picked them off. I only used alcohol once everything was clear just to be sure it was absolutely clean.

McMurdo 5th May 2020 8:12 pm

Re: Zx81
 
hair dryer set to high and a used razor blade

SiriusHardware 5th May 2020 8:55 pm

Re: Zx81
 
John, yes, that's kind of how I saw it going. Unfortunately it didn't happen that way.

Quote:

Originally Posted by McMurdo (Post 1243099)
hair dryer set to high and a used razor blade

Sounds like a plan: I'm a bit worried about the possibility of melting an irreplaceable bit of 40-year old plastic, though.

Refugee 6th May 2020 1:04 am

Re: Zx81
 
That sounds like roley poly glue. Just roll it up into little balls and pick them off.
A cloth dampened with solvent will get any finger marks off before you apply the new keypad.

SiriusHardware 6th May 2020 11:13 am

Re: Zx81
 
I change button membranes all the time at work and I agree that is how it usually goes, but this one was exceptionally resilient. I had to soak it in IPA and use a brass scruffle pad (normally used for cleaning soldering iron tips) before it would really start to break up so I could remove it in the usual fashion.


All times are GMT +1. The time now is 9:09 pm.

Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.