by Klaas Robers » Fri Aug 13, 2021 9:01 pm
Firstly see that the "monitor" functions correctly on the built in test signal. See that you bend the disc such that it is almost flat. The disc when running should not touch the PCB and the paper "stroboscope" (sync) disc should keep clear from the opto sensor in the PCB.
If the "centerhole is not in the center, then the disc is faulty. I think that you should have a better disc if you complain about it. The edge of the disc should be constant within about one mm. Otherwise you will also have problems with the lines of the NBTV picture.
Again: concentrate on the built in test picture. Only if that is Ok try to look at the pictures of the CD.
The output of the CD-player gives you a few extra problems that you can solve only after the built-in test picture displays correctly. The problems are:
1. the polarity of the video signal,
2. the amplitude (strength) of the video signal,
3. the low frequency response of the CD-player.
Ad 1: the Mindset CD has the video signal in two polarities, try them both en use the one that works. Preferably use an old CD-player used in an audio sound system. They useally have a "Line output". Use that output. Originally this output should have a defined polarity and amplitude. This should solve all three problems.
Ad 2: unless audio sound, which may have all amplitudes (strengths), a video signal has a well defined optimal amplitude: 1 volt peak to peak. If you have an oscilloscope, look at that video signal and adjust the "volume" to at least 1 volt peak to peak. Quite some portable CD-players cannot reach this amplitude from their ear phone output. Adjusting potentiometer R7 on the PCB may also help you, but the n you loose the optimal setting for the test signal. Using the oscilloscope gives you also information about the polarity of the output signal. It should have sync pulses going negative.
Ad 3: Audio does not go lower than 20 Hz. NBTV video should go as low as 2 Hz. The old line output goes this low, ear phone outputs don't. However this does not affect the functioning of the picture display, 20 Hz should do. But the fidelity of the pictures is best with the 2 Hz output. So try different CD-payers. A CD-player good enough for sound may not be good enough for NBTV video.
Good luck, you may need it.