Only backlight is working, neither image nor audio, 55PUS6162/12
Overnight our Philips TV (55PUS6162/12) started behaving badly.
When plugging the TV in it turns on by itself. But only the backlight will turn on, the screen will stay completely black and no sound will play. It’s also not possible to turn off the TV via the remote (there’s no power button on the TV itself).
When contacting Philips customer support (after giving a couple power cycles a try) they gave us a software upgrade that we should install via a USB stick, but given we don’t have any image we don’t know if it actually worked. Only thing we know is that it didn’t fix the issue we had, but maybe we have new software on the main board now :D
Given the current situation I would have to ship the TV to a repair shop, which is ridiculously expensive where I live, so I decided to open up the TV instead and give it a try at manually fixing it.
Unfortunately neither the power supply board nor the main board have any visible damage like bulging capacitors or burned components.
I did a couple checks on diodes and transistors in the circuit, some of which behaved weirdly, but I guess measuring in circuit is not really reliable. Before unsoldering anything I wanted to get a second opinion though.
I also tried to measure standby voltage, but it’s not clearly labeled. But I guess it is the 3.5V label, aka the lowermost pin. Measuring the voltage on that I saw a steady and really quick drop. Plugging in and positioning my multimeter it already was at ~2V and within 5 to 10 seconds it’s down to 8mV, which might as well be 0V in the context. The behavior is the same with the Main Board and/or backlight unplugged.
Which component could cause that behavior?
What other measurements could I do before unsoldering anything?
Ist dies eine gute Frage?