Posted By
TLC
on 2022-10-02
16:39:48
|  Re: Video interferences
A friend of mine has experienced similar problems when he powered one of his computers from a cheap modern wall-outlet SMPS.
The story probably goes like this. The SMPS produces some amount of periodic high frequency noise, which (the HF components, that is) would be superponed to the signals inside the computer, including video out. Modern displays have inputs of very high bandwidth, picture properties are only controlled by particular sampling frequency and later (post-A/D, digital) stages, but not analog input bandwidth limit filters. Some of the high frequency noise content gets past the A/D stage undersampled (i.e. spreading then over the entire useful video band), and ends up displayed as an interference-type noise.
I believe that this case here should probably be similar to that one. The SMPS of the RPi adds some HF interference. The devices are grounded together, consequently, the HF noise should be found everywhere in the whole system.
(No particular safe bets from me to solve that, sorry. If I had problems like that, I'd try to get rid of the HF noise off the power supply voltage. Maybe I'd look for some solution to filter the PSU voltage of the RPi, a different RPi PSU, maybe, an old linear (non-SM) PSU, which is known not to produce HF interference.)
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