Hi there!
I got a broken TV in my hands. It doesnt power on at all. It was clear from the first time the issue was in the power supply.
I checked secondary diodes first, all tested good
No AC power in the secondaries
Went back to the primary side. No AC getting to the primary. Transformer is good (~2ohms)
Mains rectifier and HV capacitor seem 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 HV 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. 0,5-1 Hz
HV (startup) is correctly fed to pin 8, 320 volts there...
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)
Thanks!!
I got a broken TV in my hands. It doesnt power on at all. It was clear from the first time the issue was in the power supply.
I checked secondary diodes first, all tested good
No AC power in the secondaries
Went back to the primary side. No AC getting to the primary. Transformer is good (~2ohms)
Mains rectifier and HV capacitor seem 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 HV 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. 0,5-1 Hz
HV (startup) is correctly fed to pin 8, 320 volts there...
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)
Thanks!!