LG 32LD550 won't turn on - HELP!

[budm]

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

"Error pin and?" Error pin and GND pin (or Chassis GND) of the POWER SUPPLY BOARD connector.
"Are you talking about IC1002?," No, the PWM IC P/N BD9270 is on the bottom side of the power supply board. Look at the pictures of the power supply board bottom side, the service manual does not give any info for the power supply board, you will have to trace out the power supply board yourself, it will be very time consuming since you will not going to find the diagram for that power supply board.

[MisterD]

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

Make sure all of the mounting screws are tightened down on both the power supply and main board, this is how these boards get there ground connections to the chassis.

I just repaired a LG 32LD450, would shut off after 15 seconds, had blinking red light, problem found slightly loose ground/mounting screws on power supply board that looks just like yours, get them good and tight.

[yrn11]

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

"Error pin and?" Error pin and GND pin (or Chassis GND) of the POWER SUPPLY BOARD connector.
"Are you talking about IC1002?," No, the PWM IC P/N BD9270 is on the bottom side of the power supply board. Look at the pictures of the power supply board bottom side, the service manual does not give any info for the power supply board, you will have to trace out the power supply board yourself, it will be very time consuming since you will not going to find the diagram for that power supply board.

Well I've checked it up, it's close to 0 Ohms.
as for Q405 & R419 as I've written above -
R419 resistance - is very close to 1k Ohms, it's about 0.9k Ohms.
Q405 C - E resistance - is also very close to 1k Ohms, 0.95k Ohms.

Make sure all of the mounting screws are tightened down on both the power supply and main board, this is how these boards get there ground connections to the chassis.

I just repaired a LG 32LD450, would shut off after 15 seconds, had blinking red light, problem found slightly loose ground/mounting screws on power supply board that looks just like yours, get them good and tight.

Sounds very similar but I've checked them all...nothing..

[Agent24]

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

R419 is a 1k resistor so your measurement of 1k across it is good.

1k across the transistor may be a problem. From what I saw on your photo, your board does not have R451 or R425 so the only path in parallel between Q405's collector and emitter\ground may come through the PSU board itself.

Try disconnecting the PSU board and measuring across Q405 collector and emitter again. What is the resistance then?

[manoftheyear]

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

Hello

Might I borrow this thread a bit. I have a TV of the same brand and with many similarities although the model is not the exact same. The layout and the components are pretty much the same, the IC on this on is BD9240F.

TV goes on and blue led lights on for 5 seconds, then the tv switches off and red led comes. Screen stays black all the time.

I believe this has something to do with the backlights. Should the backlights light up if I put a jump wire from the 3.5V rail to the PWR_ON and INV_ON? PSU starts but no backlight comes. Does this tell the mainboard is OK?

How come there's a rail on Power supply marked 20V but on the mainboard it's 24V? Anyway with DMM it is 20V, all the other voltages seem to be within the spec too as far as I know.

I also tested the R419 that can be found on this one too and it is 1K, which is OK.

When the TV is on for the 5 seconds. measuring the voltage between the collector, base and emitter of Q405 and the ground I get C = 3.2V, B = 0.62V and E = 0V but all the voltages go up and down like it's trying to start the inverter a couple of times. What might cause this, anyone?

Here should be the service manual for this one: https://cdn.badcaps-static.com/pdfs/...b64fd020f0.pdf but like I said that one has the IC BD9270, mine was BD9240F.

[Agent24]

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

You should start a new thread for a different model or it will just add confusion to the thread already here.

[yrn11]

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

R419 is a 1k resistor so your measurement of 1k across it is good.

1k across the transistor may be a problem. From what I saw on your photo, your board does not have R451 or R425 so the only path in parallel between Q405's collector and emitter\ground may come through the PSU board itself.

Try disconnecting the PSU board and measuring across Q405 collector and emitter again. What is the resistance then?

Hi,

I've managed to get some time to verify it again, i'm getting almost 1K between C & E once PSU board is disconnected.

what do you suggest?

[Agent24]

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

Unless I have misread the schematic, then in that case I would suspect that Q405 is bad, or that the schematic is wrong and R418 is not 6.8k as they say it is.

Do you have soldering equipment and skill to safely remove\replace Q405?

At this point I would test it out of circuit to see what it measures across C\E, or you could measure the corresponding pads on the PCB with it removed to see if there is any change in the resistance measured.

[yrn11]

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

Unless I have misread the schematic, then in that case I would suspect that Q405 is bad, or that the schematic is wrong and R418 is not 6.8k as they say it is.

Do you have soldering equipment and skill to safely remove\replace Q405?

At this point I would test it out of circuit to see what it measures across C\E, or you could measure the corresponding pads on the PCB with it removed to see if there is any change in the resistance measured.

Yes I have, can you please point me to the name of the transistor?
I've looked it up on aliexpress and couldn't find anything similar.

[Agent24]

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

It's a 2SC3052, and going by the 'LF' on the package, it's the -F variant (2SC3052-F)
I see them on eBay for example http://www.ebay.com/itm/2SC3052F-SMD...item2ede6625a8
There are many other transistors you could probably use too though, like the MMBT3904 or MMBT2222A, which may be easier to get.

Of course, you should verify if it's actually bad before buying a replacement.

[yrn11]

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

It's a 2SC3052, and going by the 'LF' on the package, it's the -F variant (2SC3052-F)
I see them on eBay for example http://www.ebay.com/itm/2SC3052F-SMD...item2ede6625a8
There are many other transistors you could probably use too though, like the MMBT3904 or MMBT2222A, which may be easier to get.

Of course, you should verify if it's actually bad before buying a replacement.

will this do the job?
http://www.aliexpress.com/item/2SC30...375273839.html

[Agent24]

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

will this do the job?
http://www.aliexpress.com/item/2SC30...375273839.html

It's the correct part number, so if that seller is reputable and the parts are genuine, then yes.

Assuming of course Q405 is bad. You have not told us if you removed and tested it out of circuit yet.

[yrn11]

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

It's the correct part number, so if that seller is reputable and the parts are genuine, then yes.

Assuming of course Q405 is bad. You have not told us if you removed and tested it out of circuit yet.

well in order to validate it, I've ordered a soldering tip that is small enough...so it will have to wait a bit.

[Agent24]

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

Have you ever done SMT soldering before? The smallest tip is not always the best. 1mm chisel is good for parts about this size, but I sometimes use my larger 2.5mm chisel tip sideways, as it's only about 1mm thick. The worst are those long and very thin 'needle' point tips.

There are a number of good videos on YouTube if you haven't done SMT parts before.

[yrn11]

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

Have you ever done SMT soldering before? The smallest tip is not always the best. 1mm chisel is good for parts about this size, but I sometimes use my larger 2.5mm chisel tip sideways, as it's only about 1mm thick. The worst are those long and very thin 'needle' point tips.

There are a number of good videos on YouTube if you haven't done SMT parts before.

Well I finally got all the stuff and replaced it, but got nothing.
same V readings are there on Q405 (0.67, 0.04) as for resistance it's now 0.
as for resistance I got
R419 - 0.9
QR05 (C-E) - 0.9

Any idea?

[darlaw]

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

possible reason is broken core drive transformer, there are two the same type.