Vestel 17IPS12

[An-klamm]

Hello!
I am in despair with a Vestel 17IPS12 power supply.
With the TV, the backlight just stays off.
( Backlight tested with backlight tester = IO)
12V on the secondary side are there and constant. Voltage of the backlight is when switching on once briefly at about 60-70V and then drops slowly. (up to about 36V I have observed it whether it then drops further I do not know).
But I am sure that the problem is on the primary side, because the DC high voltage is only at 295V. I expected about 330V (with an input of 230V 50Hz).
I checked the mosfet in the component tester and it seems OK. Tested optocoupler for feedback pin (feedback is also pulled down to about 0.3V).
About 16V is coming from the winding (I don't know what it's called. Secondary winding?) to supply the quasi-resonant control (1Q001).

What else can I check?
What voltage should be on which pin of the 1Q001 for it to start and switch the mosfet?

[Diah]

Re: Vestel 17IPS12

you wrote you have 12V...... what about 5V STBY ? and 24VCC ???

what did the front LED indicator do when you power the TV on ?

did you disconnect the MB from Power boards and tested the Power boards as stand alone to see if it produce all V above ???

and what V give you the LED tester for all Groups?

[arizanotlari]

Re: Vestel 17IPS12

Dont touch primary side. psu working good. check c113 and replace led strips.

[An-klamm]

Re: Vestel 17IPS12

One leg of the optocoupler probably had no contact. Now the TV is working again.
So it was probably only the optocoupler. The old one had a voltage drop of 0,5V, although the datasheet says maximum 0,2V. With the new one it is about 0.1V and now everything works fine again.

[nomoresonys]

Re: Vestel 17IPS12

Good work, good thing you stuck with verifying the powerboard and didn't jump to any conclusions, good troubleshooting is about not assuming anything.