Dukes909 wrote: ↑Wed Oct 06, 2021 3:52 am
Does anyone know if the TFW8B Atari 2600 mod works well on the Sinclairs?
The TFW8B COMPOSITE VIDEO MOD V2.1 - ATARI 2600/7800 is a similar circuit, so if my design does not work, it’s likely that this will produce similar results.
Part of the problem is that the video signal from the ZX81/TS1000 is not to the broadcast standard. The computers were designed for use with black and white (monochrome) CRT televisions of the day. These being totally analogue designs, they were much more forgiving if the timing or signal levels were not quite right. Further more, most would work if the synchronisation signal included in the video signal was to the old standard. The ZX81/TS1000 video generation design only produces the bare minimum in terms of video signal complexity in order to work with black and white CRT televisions.
LCD televisions and monitors work completely differently. They sample the analogue video input signal, and convert it to a digital signal. Then it’s processed. It’s examined to find the sync part of the signal. The picture information goes to a frame buffer memory, so that the correct information can be supplied to the matrix grid of the LCD pixels.
Generally speaking, they are looking for a video signal that is to the established broadcast standard (the analogue standard that was current before analogue TV was switched off). Different designs of TV vary enormously in which 1980s computers they will work with.
You appear to have been unlucky in that you have two TVs that are not happy and won’t work.
Unfortunately it’s the luck of the draw on what works and what does not.
The grainy picture is possibly noise in the signal. Pokemon’s design fixes this, but he is as far as I know not producing them at the moment. And we don’t know if this will change.
It may be possible to improve the picture by using the brightness and contrast controls.
Mark