LG 32LD450 shuts off after 15-25 seconds

[budm]

Re: LG 32LD450 shuts off after 15-25 seconds

OK, so we now know that the pfc is working but some how the Power ON (PS-ON) disappear and causes PFC and the rest of the switched power supply to turn off, but the standby 3.3V is always present, so something on the main board is going bad, it can be caps, IC, bad solder joints, etc.
You should also look to see if the INVR ON (BL-ON) also disappear or not too.

[MisterD]

Re: LG 32LD450 shuts off after 15-25 seconds

Deleted repeated reply.

[MisterD]

Re: LG 32LD450 shuts off after 15-25 seconds

Sorry Bud my meter was set on AC, measured across main filter caps got 360 VDC while set was on and working, It was on about 15 mins this time and shut down with flashing red light, while shut down voltage across main caps is 168 VDC.
After unplugging and letting caps bleed down to 30 volts, plugged back in and got same 168 VDC while off and 360 VDC while on and working.

[budm]

Re: LG 32LD450 shuts off after 15-25 seconds

"Voltage across main caps flucuates from 781 down to 481 V AC while set is on and working, then drops to 222V AC when backlights are flickering, set shuts down then voltage across main caps is 368V AC, power light is flashing red like a car turn signal everytime it shuts down, but I can power right back on and it may last only 15 secs to several minutes depending on how long it was left off. Any help is appreciated" You need to verify the DCV between the two legs of the main filter cap to see if the PFC Voltage circuit is working or not when TV is turned on. The Voltages you report are not right. Make sure to set the meter to DCV and measure right between the legs of the cap.

[MisterD]

Re: LG 32LD450 shuts off after 15-25 seconds

Here are some pictures of the boards and a drawing of the main rail connector on the power supply with voltages I read with volt meter, sorry but my camera will not take good close ups. The Brown colored wire is the power on 3.3VDC

Thanks in advance, your help is apprecitated

I hope budm will chime in, he is always very helpful.

[MisterD]

Re: LG 32LD450 shuts off after 15-25 seconds

The mainboard rail connector is Not labeled PSON but is actually labeled as power on, all voltages on the ps rail connector are normal As far as i know and all voltages drop to zero when the set shuts down, Except there are 4 pins with 3.4 volts and this voltage remains the same even when it shuts down.
Backlights either flicker or flash off then back on 3 to 4 times right before it shuts down.

Voltage across main caps flucuates from 781 down to 481 V AC while set is on and working, then drops to 222V AC when backlights are flickering, set shuts down then voltage across main caps is 368V AC, power light is flashing red like a car turn signal everytime it shuts down, but I can power right back on and it may last only 15 secs to several minutes depending on how long it was left off. Any help is appreciated

Also this TV stayed on this time with the back off for about 20-25 minutes before shutting down the first time then gradually had less time with each time I turned it back on, getting down to as low as only 15 seconds.

[CapLeaker]

Re: LG 32LD450 shuts off after 15-25 seconds

you got to figure out why your PSon signal disappears. No wonder the PSU is shutting down if there is no PSon voltage sent from the main board.

[MisterD]

The longer it sits off it may stay on longer, I have had it stay on up to 5 minutes after sitting several days unplugged, once it gets to the point where it only stays on 15 seconds it will shut down and go to flashing red light but can always be turned right back on and will go about 15 seconds every time.

normal power when it is on has blue light, I did measure the power on (pson) voltage on ps board rail at 3.3v but once it shuts down the 3.3v is gone, could I take two AA batteries and wire in series to get 3 VDC, and hook to the 3.3 rail on ps board to see if it stays on and if it does would that indicate the main board is the problem? And ps board is good?
Sorry my camera is not here at this time to take pics of boards.
Thanks for all replies