This happens because of the color decoder in the TV. A TV color decoder has a switch that makes the TV image black and white when the received signal does not have sufficient power. Your TV color decoder switch remains in the black and white position (the TV receives weak signal or the TV color decoder is damaged).Replace the TV antenna, try an antenna amplifier or a digital receiver before the TV.
Most power conversion devices contains coils, such as transformers or inductors. These components use electromagnetism to convert AC main power to low-voltage DC power. The varying magnetic fields generated by these components can cause them to physically vibrate at high frequency, resulting in a high-pitched noise.
https://www.howtogeek.com/200466/why-do-some-ac-adapters-and-power-supplies-make-a-whining-noise/
sansui tv code for service menu press menu button on remote ,then channel-, then enter 1947 code services mode will open.
rimot par sarvis menoo pres menoo batan ke lie sansui teevee kod, phir chainal-, phir 1947 kod darj karen seva mod khul jaega.
I'm guessing a power surge from the returning power burned something up. You should have all your electronics plugged into surge protectors at a minimum. The best protection is a UPS (uninterruptable power supply).
