Quadro LED-40TN42S2T2HEVC

[Guerilla3]

Hello.

PS Vestel 17IPS62
MB Vestel 17MB140

TV died while in standby mode. Doesn't react to remote, or onboard on button in any way. No backlight. Standby light is off. Transformer buzzes silently.

Quick visual inspection; no burn marks, caps look ok.

Multimeter check unpowered; fuses are ok, electrolitic caps near or at rated capacitance, diodes ok.

Multimeter cold side all boards disconnected from PS;
mb connector 12v - 2.03v, stby - (-)2.96v, bkl and pwm 0v
inverter connector 24v line is 6v

all boards connected; 12v and 24v same as above, no easy access to other pins.

Guessing the issue is the PS, but I have no idea what to look for next. Considering just buying a new board, but would like to confirm its the PS and find the exact problem if possible. Thanks.

[dskall]

Re: Quadro LED-40TN42S2T2HEVC

What is voltage across main capacitor?

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

I am assuming you mean the 2 400v capacitors, they are ~315v.

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

OK, on second measurement I'm getting 12.3v on 12v, and 35v for inverter now.

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

0v for stby, bkl and pwm

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

Now everything works. I'm guessing cold joints or something where the culprit, as I tested the voltages multiple times, with different board setups, and also I waited overnight to confirm the symptoms before opening it up. Now I will leave the tv disconnected overnight again, check if it works tomorrow and report back.

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

TV works well today. At least I can confirm the problem was the PS.
For future reference the working voltages when only the PS was plugged in without any other boards were: 35v for the Vled pins, some volts for the CH_1,2,3,4, 12v on 12v pins, and 0v for stby, bkl and pwm.
Thanks dskall for replying.

[dskall]

Re: Quadro LED-40TN42S2T2HEVC

If you have problems again you will need to resolder things like the transformer and connectors.

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

Will do, thanks again.

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

TV stopped working again. Tried reflowing most of the hot side, also transformers and electrolytic caps. DC voltages same as before for 12v and bkl. Main caps at 300+v.

[Guerilla3]

Re: Quadro LED-40TN42S2T2HEVC

Tried reflowing FETs, ICs and optocoupler.
Current situation is same as before; 12v line is 2v, and 35v line is 6v, both are lower by about 6x the needed voltage.
Main AC caps, and diodes before transformer are 300v+.