50pg20 Power Cycling When Power Applied

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I really appreciate your time and effort with this problem.. it's hard to believe that the two main boards may have the same problem... I've taken up enough of your time on this... Your great at what you do ! If you have any other suggestions I would love to hear them.. I'll try to contact LG to see if they may have a solution, although the TV is no longer supported... Thanks again! Vladas

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Thanks again for your help with this standby power issue!

[tom66]

Re: 50pg20 Power Cycling When Power Applied

I thought you changed the Z-sustain?

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Sorry about the delay.. Yes I did change out the Zsus board... if I unplug it the TV still cycles on the relay... Would you happen to know what the component labeled TH203 next to the 5v voltage regulator is? One side is 5V the other very low (@10 mv)... Thanks!

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Can I have a pic of TH203? It sounds like a thermistor.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

To the left of the 5V voltage regulator on heat sink...

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Interesting -- looks like a temperature sensor. I don't know what that is doing there, other than just measuring overall ambient temperature of the set.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

OK, there is three LED's I believe that indicate system temperature... It could be measuring this temperature from next to this regulator.. Interesting though , when I tried to measure resistance across it, it did a high pitch scream and arc'd slightly..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

OR... perhaps... it may be thermal compensation for the diode to avoid failure from hot spot localised heating... potentially.
I would focus on what you have and don't have:
- You most likely have stable 5V standby as TV attempts to power on and off
- Since control board LEDs are firing, 5V main is probably good.
- How are Vs, Va with and without Y- and Z-sustain removed?

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Yes, 5V volt is good, M5V is jumping to 3.2V in Run, and cycling back to zero, on and off... Vs is good at 193V and Va is good at 65V...

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Is it possible that the 5V regulator is faulty and under load it isn't supping enough turning the circuit on and off?

[tom66]

Re: 50pg20 Power Cycling When Power Applied

M5V is definitely a problem. What's it do when the control board is unplugged?

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

A Training manual I'm using as reference...

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

No power cycling when Main board is unplugged, though no power to other circuits, other then led on small green control board... When just small green control board is unplugged and main board is connected -still cycles..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

What's M5V measure with control unplugged?

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

On page 50 #3 of the manual it says that M5V vcc is shorted when cycling is present.. There is no short that I can find..

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

M5V measures 0V with control board (main) unplugged.. Cycling 3.2 volts when plugged in..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Odd....

Can you get a hairdryer to heat up the board, then see if the cycling stops, or if the voltage increases?

Also, how is the 12V and 16V line?

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

That's a great idea... Now am I looking for 5V on M5V (Board plugged in) with heating of the board?.. Its 3.2V and cycling when plugged in..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Yes, but before you do that, please also measure the 12V and 16V lines.