LG 32LD450 shuts off after 15-25 seconds

[MisterD]

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

The power supply/inverter board mounting screws were loose and I believe by tightening them down I have resolved the problem, left this tv on for 5 hours yesterday and 3 hours today with no failure.
Since the backlights either flickered or went off and back on a few times right before the tv shut down, I think the inverter circuit having a poor ground (due to the loose screws)was the cause.

[MisterD]

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

If you look at post 4 at the PS picture you will see that there are four mounting screws but 3 of them are black and one is chrome, there are 2 flat ground tabs on top of the board as well as the solder type ones on the back of the board.
I put the chrome screw in the bottom right just as it was before I removed the board, the bottom left screw is marked black on the circuit board but both top and bottom right have the flat chrome tabs, I'm wondering if someone else has worked on this tv sometime and used coated black screws where they should be chrome to make good ground connections at the flat tabs.

[budm]

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

May be loose Ground of the circuit board mounting holes which are also used for Grounding the boards to the chassis, I hope that was it.

[MisterD]

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

Yes I lost both PS-on and Inv-on, but now after removing and reinstalling the PS board the tv is working normally, I have removed the resistor and battery, so I'm not forcing on the PS now but tv works like it should, has been on for 2 1/2 hours now.
Not sure what I did that fixed it. Could loose ground/mounting screws on PS board be possible?

[budm]

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

Bud, if the Inv on/off lost voltage to that connection only at the connector on the PS rail would that cause the TV to shut down like this one was doing?

Thanks for the help to all, I appreciate it.

The INV_ON signal is sepearated from the PS-ON (PWR-ON) signal, it seems to me that you lost both the PS-ON and INV-ON, isn't that correct.
Since you can force on the power supply and backlights and the TV keeps on working with that setup then that just about eliminates the power supply and backlights inverter problem.

[MisterD]

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

Bud, if the Inv on/off lost voltage to that connection only at the connector on the PS rail would that cause the TV to shut down like this one was doing?

Thanks for the help to all, I appreciate it.

[MisterD]

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

Not sure what I did but whatever it was is the reason the backlight stayed on during the last forced on of the power supply because now the tv has stayed on over 1 hour and 25mins without fail.
1. I removed and inspected the power supply board and re-installed it and tightened down ground/mounting screws. 2. Had my volt meter on the 20v range while hooked up across one of the main caps, I forgot to switch it back to HV range before turning on the tv, fried the meter( a cheap one)

3. Completely removed the wire harness that goes from main board to PS to seat 1k resistor in place in connector to jump 3.5v to Inv on/off for testing. 4.Removed test equip,re-assembled and tested the TV with the back on.
I'm not sure if the PS wasn't grounded good or if was a bad connection at Inv on/off since the backlights would either flicker or flash off/on 3 to 4 times prior to the tv shutting down.

[budm]

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

to get this straight. Since you have the psu "hardwired" everything is ok?

+1

[CapLeaker]

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

To get this straight. Since you have the PSU "hardwired" everything is OK?

[MisterD]

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

I had my meter hooked up monitoring the command signal and the backlights would flicker or flash on/off 3 or 4 times then go off first before the power on voltage dropped out but it did drop out immediately after backlights went off.

[budm]

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

I had the 1k resistor leads shoved into the rail connector where the wire leads go in, and must not have been making a good connection because now that I have shoved them in more, the backlight has NOT gone off at all with the PS forced on and running about 45-50 minutes.
So now I'm thinking the PS is good and the main board is the issue after all.

Lost of command signal is not the function of failed the power supply if the STBY is good.

[budm]

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

Bad caps can look normal.

[MisterD]

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

I had the 1k resistor leads shoved into the rail connector where the wire leads go in, and must not have been making a good connection because now that I have shoved them in more, the backlight has NOT gone off at all with the PS forced on and running about 45-50 minutes.
So now I'm thinking the PS is good and the main board is the issue after all.

[MisterD]

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

Bud, I have not changed any capacitors on the power supply board none of them are bulged out, could they be bad anyway?
They are Su'scon brand caps, main filter caps (there are two) both are marked sk 105 degree C 1021M all others are marked SG 105 degree C, the pair of main caps are stuck down on the board with the value and voltage facing into the glue. What should I do now? Order and change caps anyway? Do you think the main board is ok?

Thanks

[budm]

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

The backlights inverter circuit needs >360DVC to run so when that PFC Boosted Voltage drops down, then the inverter circuit will go into shutdown. The problem is that we do not know for sure if the PFC circuit drops out due to too much current demand by the inverter circuit or it drops down due to false in the PFC and cannot supply the needed current by the inverter circuits. Did you change all the caps on the power supply board? Inspect the main filter cap closely for the ESR and the capacitance.

[MisterD]

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

The voltage across the main cap drops to 167 VDC, when the backlights go out, I just checked it with my meter hooked up it dropped suddenly to 167v, then backlights went out immediately after that, I noticed the voltage across the main caps climbing and dropping while ps is forced on and backlights go out, went from 167 to 377 then drops keeps fluctuating.

It didn't do the fluctuating immediately, I just left the ps forced on even after backlights went out, then after a few minutes it starts the voltage fluctuation. The connector to the main board is unplugged.

[budm]

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

So when you do the force on using the resistors on the POWER ON PIN and on the INVERTRER-ON pin the backlights still goes out after 15 seconds. So does the PF VDC on the main filter cap also drops down or it still stays at 360VDC or so?

[MisterD]

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

On the power supply rail connector I jumped through a 1k resistor from 3.5 to inv on/off, used 3v battery connected to power on, voltages remain on power supply rail but backlights are going off after about 15 seconds just like it did when tv was shutting down, now I wonder if the PS board is the problem, shouldn't the backlights stay on as long as I have the necessary voltage to inv on/off?
Also if I unhook power and let it cool down the backlights stay on longer the first time then the cycle gets shorter after it warms up.
I have the connector from the PS board to main board unplugged at the main board during this test. I don't see any bulging caps on the PS board. Need Help to diagnose the problem.
Thanks

[CapLeaker]

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

Take the PSON pin out so you don't back feed power, then beige PSON with STBY voltage with a 500ohm resistor and the TV should be alive. You may also have to do that with the back lights BLon.

[MisterD]

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

Yes the INVR ON is disappearing too whenever the tv shuts down, only the 3.4 standby remains, I have 2 AA 1.5 v batteries wired up in series to equal 3 volts, do you see any reason why I should or shouldn't cut power on (brown wire) from main board to ps and hook 3v battery to power on at ps connector and see if the tv comes on and stays on while battery is hooked up? Or jumping from 3.4 standby with 1k resistor to power on (PSON) ?

Thanks Bud.