I got a broken TV in my hands. It was clear from the first time the issue was in the power supply.
There is no power at all on any secondary. Checked secondary diodes first, all tested good
No power in the secondaries
Went back to the primary side. Transformer is good (~2ohms)
Mains rectifier and HV capacitor seems to be good (storing 320 volts of DC for a long time) (it runs on 220V)
So it all seems to be pointing at the electronics between the capacitor and the primary.
I can hear a super low, "twich...twich"...very very low. Aprox 0,5 -> 1 Hz
Checked switching Mosfet (2N70), tested good with the multimeter diode "trick" that charges the internal capacitor and starts conducting
Checked the 100Kohm parallel-series resistors that feed the mosfet's source and is good. Checked all diodes around and look good
I downloaded the datasheet for the controller (LD7575, attached) and after reading everything, I can't see what's causing all this switching.
I checked RT, CS, COMP and they are all swinging up and down at the same rate (once every 1-2 seconds)
Vcc for the LD7575 is swinging from 10 to 16volts.
HV (startup) is correctly fed to pin 8.
Should I suspect bad LD7575?
Im attaching my PS schematic along with the controller IC:
https://www.elektrotanya.com/lien-chang_aivp-0026_for_vestel_20inch_lcd_tv.pdf/download.html Link to power supply (give it some time and a download link will show up below the preview image. It works...)
https://lib.chipdip.ru/923/DOC000923326.pdf Link to LD7575 (PS managing IC)