Agreed. Sounds like your probing flexed the PCB enough to correct an open solder joint...
Get out your soldering iron and reflow all of those power pins for starters. More troubleshooting if that doesn't work, possibly capacitors or power supply issues.
You should see the capacity / voltage ratings of the capacitors on the other side, facing the PCB. You'll have to lift them from the board.
The PS board is a single sided PCB, they are prone to bad solder joints due to thermal stress and old age. The ones you pictured are on a multi-layer board, these usually do not go bad.
Look for bad solder joints on the power supply PCB, especially at the pins of larger components (like the caps, transformers, power semiconductors).
+ pin of C2 , I would reflow ?
and of course check capacitors with an esr meter ...
Confirm if C12 is 224/50V [0.22uf] capacitor, check its value with a "proper" capacitance meter out of the circuit or simply change it.
This capacitor is near to U1 of the power supply board.
+ pin of C2 , I would reflow ?
and of course check capacitors with an esr meter ...
I do not see C12 (I also looked on the back at the smd caps near u1)
Is U1 a 8 Pin SO8 package device?. Confirm its a TEA1733. If Yes, then follow the Pin4 connected to a 2K resistor. After the 2K resistor is the C12 in series to it.
Edit: Sorry those are 0805 smd devices. Search on the copper side. Use a magnifying glass
Edit: You took photo on the component side, why no photo on the copper side?
Edit: At the same time, also check the capacitor connector to pin 6 to ground, measure ohms across it, just make sure it not shorted example high ohms [turn off power to measure it].
In general, with single sided PCBs, the THT solder joints of thermally or mechanically stressed components are prone to go bad over time. That might be the transformers, also the connectors and the heat sink mounted semiconductors.
With some experience you may be able to see the wear, it's like a ring around the pin where the solder is cracked. At some point, the pin totally looses electrical contact. Anyway, just re-soldering pins usually doesn't harm.
If a component gets really hot while in service, the solder joints also can go bad, on some boards you can see the discolouration of the PCB material, this is a hint to check the solder joints.
Electrolytic capacitors can dry out, often there's a small one on the primary side of the supply unit that is required to properly start the SMPS, from your description I would guess that's not the issue here, anyway, did you check all outputs of the supply?
OK, so the output (16V) of the PS gets active for a short time while the PS-ON voltage stays at 5V? Does the LED output the same?
To me this looks still like a fault on the PS board, located in the main SMPS. The 5V appears to come from another auxiliary SMPS, while the main SMPS gets enabled and disabled by the PS-ON control signal.
I skimmed through.
Have you been checking for shorts to ground?
I have a TV that is supposed to be putting out 24 volts to the backlight inverter.
I replaced the burned fuse on the inverter board.
It outputs 24v when unplugged. But when plugged into inverter it outputs 0v(good think it has short detection safety built into the power supply board).
I thought it was 1 of the 4 caps that was shorted.
After removing all 4 it was still shorted to the positive leg of the cap I suspected.
Turned out to be 1 or 2 of the 14 mosfets shorted to ground.
I'll be ordering them off Digi-Key for $0.50 a piece.
Oh, and what was the area you were poking around in when it decided to work?
If you can light up a diode by testiing with a multimeter then I assume the injection of like 1v @ 15ma(I don't know the real number) made a chip wake up. or it completed a circuit.
Yeap , cant see clearly, but you need to trace it and find the 2 capacitors. Its all 0805 mlcc caps.
take a close up when you find it.
For the 0.22 uF cap, you will need to take it out to measure its capacitance or simply replace it.
Just don't under-estimate small capacitors.
Edit: Just don't spend too much time on big caps. The area I asked you to search is the nerve center of everything.
Edit: From your photo It looks like Pin 4 is connected to R7 and then R7 is connected to C5. If so, this is the 0.22uf I was talking about. And Pin 6 is connected to C4. Can't see very clearly. Trace the Pins. Labelling may not be the same as your board.