Service manual for LC-42SB45UT No Power Dead

Remove all your optocoupler jumps.

Then test DC voltage on ic903, pins 1,2,4. Using hot gnd.

Then also recheck your 5v on CN902 using cold (chassis) gnd..

what is voltage now on R976 with hot gnd?

In between your responses I found a way to test the optocouplers .

I took a 330 ohm resistor and connected it to pin 1 then connected the positive DC power supply to the end of the 330 ohm, and the neg clip
To pin 2 . Then the ohm meter to the collector and emitter of the chip, pins 3 and 4 . Then you increase the voltage and as it increases the ohm's reduce and as you reduce
The voltage the ohm's should increase. One behaved nice and smooth. The other two at a certain point went to OL then began to read again.

I need to order those as well.

Nashou

I had 1 volt, not close enough to 0 is it?

No Change after the jump of 3-4 ic909. Also lost the voltages on ic903 they went down. The 5.85 volts went down to 3.9 on pin 2 for example.

So something in the ic909 circuit might be causing it?

Athanasios

I was looking at that, there is some yellowing of the PCB on the underside where the pins are soldered.

Nashou

Ok, then Q922 is working as it should and when turned on, something past it on that line is shorted and pulling that line down. At least there is not a real lot on that line.

Connected to it is: C959,R987,R930,Q917,ic901,C920,ic902. You have to start removing parts until that line voltage comes back up to normal. Where would you like to start?