Thread: Zx81
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Old 15th Mar 2020, 7:19 pm   #76
John Earland
Join Date: May 2013
Location: Middlesbrough, North Yorkshire, UK.
Posts: 442
Default Re: Zx81

Okay - an update! I have two ZX81s now, both with 16k RAM packs. Both with their own PSUs and both with their own TV cables.

My original ZX81 (the subject of this thread) works on the RF of both the portable crt TV and the LCD - though poor picture quality in both cases. I will be modifying the ZX81 to hopefully improve this. It works on about channel 36 but with wobbly picture as discussed on both the LCD and CRT TVs.

I have tried powering this ZX81 with the two different PSUs without any discernible difference in the quality of the video output on either of the two TVs.

I have also tested the ZX81 with the Sinclair RAM pack and the MEMOPACK RAM pack. Using either of these RAM packs results in the same very distorted video output which can’t be corrected with fine adjustments to either of the two TVs. I’ve tested these RAM packs on the second ZX81 and its video output remains steady and is totally unaffected by them. This ZX81 is an early model unfortunately which generates a dark screen. However, from what I can see, the picture is quite stable no matter which PSU or RAM pack I use with it. If the picture was white it would be perfect!

My assumption that the ZX81 would not save or load programs was (potentially) false because I have been using stereo cables (mono ones ordered) so I do think that this will be okay.

So, I can deduce that:
1. There is nothing wrong with either of the PSUs.
2. There is nothing wrong with either of the RAM packs.
3. There is nothing wrong with the RF leads.
4. There remains a problem with the original ZX81. Not only is the video output poor it is affected by the attachment of the RAM packs which it shouldn’t be of course.

I will of course be testing this when I have undertaken the modification. I would be grateful for any comments, advice and guidance.

Thank you all so much for your input thus far. I really do appreciate you taking the time to help me.
John Earland is offline