How bad was the wobble on the zx81

General Chit Chat about Sinclair Computers and their Clones
Crayon21
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How bad was the wobble on the zx81

Post by Crayon21 » Tue Nov 06, 2018 11:19 pm

I've heard a lot about the wobbling issue with the ZX81. how bad was it? did it really wipe out everything?

also, as far did anyone ever use this keyboard:https://archive.org/details/syncmagazine-v3_n6/page/n21 (page 23, right side), was it better, worse?
zx81: great yet flawed
Zx spectrum: masterpiece that keeps on giving

(wish it weren't so expensive) :o

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gammaray
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Re: How bad was the wobble on the zx81

Post by gammaray » Wed Nov 07, 2018 12:27 am

It was untenable. After losing patience, I bought a DK'tronics keyboard so at least pushing a real key on a heavier case would not break connectivity on the rampack.

;)
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mrtinb
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Re: How bad was the wobble on the zx81

Post by mrtinb » Wed Nov 07, 2018 5:26 am

The keyboard you link to would not help you with the wobble.

I did not have a ZX81 back in the day. The first project for my current ZX81 was to build an external keyboard.
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

Crayon21
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Re: How bad was the wobble on the zx81

Post by Crayon21 » Wed Nov 07, 2018 5:46 am

mrtinb wrote:
Wed Nov 07, 2018 5:26 am
The keyboard you link to would not help you with the wobble.

I did not have a ZX81 back in the day. The first project for my current ZX81 was to build an external keyboard.
they are two separate questions, perhaps I should rephrase:
1. How did the wobble effect the zx81 and how was it fixed
2. was the keyboard that I linked to better or worse than the original keyboard (did it have actual keys instead of pressure sensitive ones?)
zx81: great yet flawed
Zx spectrum: masterpiece that keeps on giving

(wish it weren't so expensive) :o

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TMAOne
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Re: How bad was the wobble on the zx81

Post by TMAOne » Wed Nov 07, 2018 6:17 am

Crayon21 wrote:
Wed Nov 07, 2018 5:46 am
1. How did the wobble effect the zx81 and how was it fixed
Yes, the wobble was really bad, and it could and would easily wipe out your laboriously pecked-in program in an instant, leaving you with only The White Screen of Death. :evil:

I think there were almost as many "solutions" to this problem as there were ZX81's. Myself, I tinned the edge connector of the motherboard to make the contacts thicker and softer. I have heard of people using a wad of Blue-tack between the cases, or mounting both the computer and the RAM pack on a piece of plywood to keep the connection stable.
Crayon21 wrote:
Wed Nov 07, 2018 5:46 am
2. was the keyboard that I linked to better or worse than the original keyboard (did it have actual keys instead of pressure sensitive ones?)
I was lucky enough to pick up one of these recently. It is simply an overlay that pushes a plastic dimple into the original keyboard underneath. I find it an improvement, but a marginal one.

SAM_1330.JPG

It does give you some tactile feedback and a more positive feel than the membrane, but pales in comparison to a real keyboard. I'll never give up the one I got back in the day.

Hal Up Close.JPG

Moggy
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Re: How bad was the wobble on the zx81

Post by Moggy » Wed Nov 07, 2018 2:10 pm

The wobble ,speaking for myself, was only apparent with the Sinclair packs. I switched to the snug fit Memotech units and wobble was never a problem for me from then on likewise with the xpand.

As for the Filesixty keyboard pictured above I still have this one which is made of hard plastic and frankly rubbish, the later neoprene made replacement was better(similar to rubber keyboard mat in the Spectrum )but the keys lost their elasticity after time causing stuck keys when pressed.

these days I use a mixture of Memotech, kaydee or the superior action Fuller keyboards for daily use although at the time I found the original membrane keyboard easy to use and could shuffle around it quite quickly and unlike some found the keyword entry system quite useful.

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1024MAK
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Re: How bad was the wobble on the zx81

Post by 1024MAK » Wed Nov 07, 2018 3:57 pm

The wobble of the Sinclair RAM pack was and still is a real pain.

Vibration or slight movement of the computer or whatever you have it placed on (table, desk) causes the RAM pack to move slightly, breaking one or more of the contacts on the edge-connector (breaking, as in momentary disconnection of an electrical contact, which then reconnects again).

With a RAM pack plugged in, the ONLY RAM available to the system is in the RAM pack, so any disruption to the signals between the Z80 CPU in the ZX81 and the RAM pack will cause the Z80 CPU to read the wrong information, and then it will become confused and the system will crash. At this point, control is lost, so say bye bye to any program you may have been working on, or any game you may have been playing :twisted:

It should be noted that some third party RAM packs were less likely to experance this problem, but “RAM pack” wobble is possible with any expansion for any of the Sinclair computers (including the ZX Spectrum).

Mark

Lardo Boffin
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Re: How bad was the wobble on the zx81

Post by Lardo Boffin » Wed Nov 07, 2018 6:30 pm

I often wondered why nobody built a bus extender with a socket for the zeddy side, a piece of flexible ribbon cable and then another socket. Instant isolation of most things. Certainly overly enthusiastic keyboard mashing anyway.
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Re: How bad was the wobble on the zx81

Post by Moggy » Wed Nov 07, 2018 7:28 pm

Lardo Boffin wrote:
Wed Nov 07, 2018 6:30 pm
I often wondered why nobody built a bus extender with a socket for the zeddy side, a piece of flexible ribbon cable and then another socket. Instant isolation of most things. Certainly overly enthusiastic keyboard mashing anyway.
They did.

A few people offered such a cable I seem to recall and there was a tower system available at the time which consisted of stacked units joined to the zeddy with the cable as you describe.

Not that it is a true solution in my opinion, I have the Zxpand ribbon extender kit for the ZX80 and it crashes if accidently touched more than any ram pack I ever owned for the 81 did(yes my experience only I know),which as said earlier after switching to Memotech, I never had a problem.
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Lardo Boffin
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Re: How bad was the wobble on the zx81

Post by Lardo Boffin » Wed Nov 07, 2018 8:59 pm

Wow. I have absolutely no use whatsoever for a zeddy with 1MB of RAM but I really want one! :shock:
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
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TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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