LG 32LD550 won't turn on - HELP!

[yrn11]

Hi all,

I got my LG 32" LCD for couple of years now and out of the blue it went dead.
it started by having from time to time image freeze with vertical lines, thought it's a bad caps issue, so I've replaced them all (see attached pics), after that it worked for couple of days and now it won't turn on at all, only the red light is blinking, I've used a meter and saw that the "power on" voltage is 3.5 instead of 20v (all others have ok voltage).
Once TV is turned off it shows 0 volt and once on it shows 3.5V.

what could be the issue?

[Agent24]

Re: LG 32LD550 won't turn on - HELP!

The power connector is in a dual row configuration so one pin (the blue wire) is Power On and the other one next to it is for the 20v supply rail. The wires will be in the same physical layout as the names printed on the board next to the connector.

A Power On signal voltage of 3.5v is normal, 20v would be very abnormal.

But one thing I don't understand.. You said already "it worked for couple of days and now it won't turn on at all" then you said "once on it shows 3.5V" So does the TV turn on or not? I'm confused.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

Ok, so i've checked the one that says 'power on' but without voltage sign on it, I will try it on today.

and let me be bit more clear:
- Once I replaced the capacitor the TV was working OK (with image freeze from time to time).
- Now the TV won't turn on at all = trying to turn it on but only the red light is blinking, it on shows 3.5v but it doesn't turn on the TV.

[flocko]

Re: LG 32LD550 won't turn on - HELP!

Were low ESR capacitors used for replacements ?

[Agent24]

Re: LG 32LD550 won't turn on - HELP!

Sounds like something could be wrong with the power supply.

The mainboard will bring that Power-On line high to 3.5v as you see now, and that tells the PSU to come up into full operating mode - which it obviously isn't doing for some reason.

The first thing to check is that the PFC circuit is working OK. Measure the voltage across one of the main filter capacitors (the biggest ones lying on their sides). You should use clip leads or test hooks if you can to connect your meter, and be very careful not to let the probes slip or your fingers get anywhere near them!

With the TV in standby, you should see a DC voltage somewhat higher than your AC line voltage. When you press the power button, the voltage should rise to at least around 360v DC or so.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

Sounds like something could be wrong with the power supply.

The mainboard will bring that Power-On line high to 3.5v as you see now, and that tells the PSU to come up into full operating mode - which it obviously isn't doing for some reason.

The first thing to check is that the PFC circuit is working OK. Measure the voltage across one of the main filter capacitors (the biggest ones lying on their sides). You should use clip leads or test hooks if you can to connect your meter, and be very careful not to let the probes slip or your fingers get anywhere near them!

With the TV in standby, you should see a DC voltage somewhat higher than your AC line voltage. When you press the power button, the voltage should rise to at least around 360v DC or so.

I've measured the capacitors they are showing correct values.
also verified all fuses.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

Were low ESR capacitors used for replacements ?

The same uF was used and on some higher voltage value but never lower values.

[Agent24]

Re: LG 32LD550 won't turn on - HELP!

I've measured the capacitors they are showing correct values.

Correct value as in capacitance, or what?

Can you list all the output pins on the PSU by name and what voltage you measure on each of them, both when the TV is in standby and when you press the power button.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

Correct value as in capacitance, or what?

Can you list all the output pins on the PSU by name and what voltage you measure on each of them, both when the TV is in standby and when you press the power button.

See attached pic.

[budm]

Re: LG 32LD550 won't turn on - HELP!

Yo u have all the correct Voltages but the main board is not sending the INV ON/OFF command to turn on the backlights.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

Yo u have all the correct Voltages but the main board is not sending the INV ON/OFF command to turn on the backlights.

So what should be my next step?

[budm]

Re: LG 32LD550 won't turn on - HELP!

Did you check the DCV on the filer cap as requested on post 5 to see if the PFC Voltage booster is working or not. You need to follow the instruction.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

Did you check the DCV on the filer cap as requested on post 5 to see if the PFC Voltage booster is working or not. You need to follow the instruction.

Yes, it was around 308.

[Agent24]

Re: LG 32LD550 won't turn on - HELP!

Yes, it was around 308.

I'm not 100% sure but that seems a little low. What is your AC line voltage?

[budm]

Re: LG 32LD550 won't turn on - HELP!

If your AC is 230VAC, the cap should have 325~330VDC in standby mode, so if you are getting only 308VDC, that is not right.
BTW, this Voltage has no relation to the missing BL-ON signal. Are you sure your meter is OK first?

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

I'm not 100% sure but that seems a little low. What is your AC line voltage?

AC is 220, I've re tested the main caps.
Standby - 325
On - 389

[budm]

Re: LG 32LD550 won't turn on - HELP!

AC is 220, I've re tested the main caps.
Standby - 325
On - 389

So what happen to the 308VDC reading as shown in post 13? We are chasing the problem that is not there due to wrong information.
So right now your power supply is good and the problem is due to the main board is not sending the command signal.

[Agent24]

Re: LG 32LD550 won't turn on - HELP!

AC is 220, I've re tested the main caps.
Standby - 325
On - 389

OK, that sounds good to me for 220V mains.

[yrn11]

Re: LG 32LD550 won't turn on - HELP!

So what happen to the 308VDC reading as shown in post 13? We are chasing the problem that is not there due to wrong information.
So right now your power supply is good and the problem is due to the main board is not sending the command signal.

Ok, so what should I check on the main board.
The 308 was a wrong reading.

[Agent24]

Re: LG 32LD550 won't turn on - HELP!

We need a schematic at this point I think, I found 3 for your model on ElectroTanya but for different variants. It should be written probably on a sticker inside somewhere which one yours is.

Should say 32LD550-XX where XX may be UB or some such code, We probably need to know which one to get the right schematic. (I say probably, because sometimes they are all exactly the same and the code may only refer to something like the case colour or design which has nothing to do with the electrical design)