[old_tv_nut]

I left comments under your video, copied here:

Dark band on channel 2 with no signal - this is probably a slight oscillation coming from the power supply - nothing to worry about, should disappear when you have a normal signal.

Snowy picture with a signal - needs to be diagnosed and fixed. Could be anywhere from a broken antenna wire, or something in the tuner; not likely to be the IF though there is a tiny possibility.

Range of the brightness control with picture completely black may be normal due to sloppy design.

Change of picture size with brightness or fine tuning bringing up stronger image - probably normal. Just make the vertical size a bit bigger to hide the black edges.

Vertical collapse when changing channel - big noise in the signal momentarily kills the vertical - needs to be diagnosed and fixed.

Where you point to color at the bottom, all I see is reflections from the table.

Not sure what the squirmy noise is from, probalby some other nearby equipment? You may have a bad signal connection, as I said above.

The color interference you point at (which I can't see very well) could be an interfering signal of some kind just like the squirmy noise - need to get a good strong noise-free RF connection before going further.

The coarser, stronger interference on channel 8 with no signal is unknown, but again, no use trying to chase something that likely occurs only in a no-signal condition, until you can show that it occurs with a good signal.

In summary, on channels with no signal, you should expect to see snow and hear white noise. You do see snow, so don't worry about it until the strong signal problems are fixed. However, if you don't hear audio white noise, there is something wrong with the sound section.