LG 42LB5600 standby light works but no picture and clicking sound

[jmandawg]

Hi all,

I have a LG 42LB5600 when plugged in the red standby light is illuminated. i can hear a faint clicking sound coming from the part# 14S-LM01 (transformer? in middle of the board) When i press the power button, the standby light turns off but the display does not turn on.

I do get voltages across the fuses and the large caps (did not check the small ones) but no voltage out the led power (top red and black wires).

Did not see any burn marks or bulging caps.

The faint clicking is only when the TV is turned off.

Any ideas?

[dick_barton]

Re: LG 42LB5600 standby light works but no picture and clicking sound

Can you give the voltages on the connector as shown on the circuit board
eg
Pin No. Name Voltage
Pin 1 GND 0V
Pin 2 ON/OFF 3.5V
PIn 3......etc


and what volatge do you have between the two legs of C610

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

i can only test the pins on the top without turning the board over. Here's what i got from top pins with tv turned on:

pin1 GND: 0
pin2 12v: 11.91
pin3 12v: 11.91
pin4 GND: 0
pin5 24v: when i touch the prob to it it's goes from a voltage around 17v and immediately drops to 1v
pin6 GND: 0
pin7 3.5: 3.5
pin8 3.5: 3.5
pin9 PWON: 3.3

[dick_barton]

Re: LG 42LB5600 standby light works but no picture and clicking sound

How about DRV_ON. There are two sets of pins running in parallel on that connector so I think you missed out some of the readings.

You need to check the diodes under the silver heatsink. Use your meter in diode mode.

If this is similar to your power supply can you check the two items identified

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

Here is a pic of the underside of the board. and here are the other set of pins:

pin1 GND: 0
pin2 NC: -
pin3 12v: 11.91
pin4 G: 0
pin5 24v: goes from around 17 -> 1v when touched with probe
pin6: NC: -
pin7 3.5: 3.5v
pin8 P-DIM: 1.2v
pin9 DRVON: 3.10

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

I check the 2 transistors in your image. I'm assuming i do it with the TV unplugged.

for the first one with the arrow: no reading between left and middle pin, but i got a reading between middle and right pin. (and same thing for the transistor right above it)

2nd one with the box around it. I got a voltage reading from left to middle and right to middle.

Please let me know if i'm testing them wrong.

[Diah]

Re: LG 42LB5600 standby light works but no picture and clicking sound

the 24V drops down after seconds.. mean you need to test the LED socket red probe on red and black on black then turn on.. i think it will goes high and drops down if there re shorted LED. TV will not starting.

[dick_barton]

Re: LG 42LB5600 standby light works but no picture and clicking sound

I check the 2 transistors in your image. I'm assuming i do it with the TV unplugged.

for the first one with the arrow: no reading between left and middle pin, but i got a reading between middle and right pin. (and same thing for the transistor right above it)

2nd one with the box around it. I got a voltage reading from left to middle and right to middle.

Please let me know if i'm testing them wrong.

What were the readings. Can you see the part numbers written on them?

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

the 24V drops down after seconds.. mean you need to test the LED socket red probe on red and black on black then turn on.. i think it will goes high and drops down if there re shorted LED. TV will not starting.

yes i just tested, when i turn the TV on the LED output jumps from 19v and then back down to zero. Do you think it's still worth trying to fix?

[Diah]

Re: LG 42LB5600 standby light works but no picture and clicking sound

its tell you have one shorted LED so the set went to safe shutdown.. take the screen apart and put it at safe place .. check which LED wont lid at start up and replace it... the set still can work with out LCD in place.. so the checking and repair easy.

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

its tell you have one shorted LED so the set went to safe shutdown.. take the screen apart and put it at safe place .. check which LED wont lid at start up and replace it... the set still can work with out LCD in place.. so the checking and repair easy.

the thing is even with the LED connector unplugged the voltage still goes from around 19v to 0v on startup. Shouldn't the voltage stay on when the connector is unplugged?

[Diah]

Re: LG 42LB5600 standby light works but no picture and clicking sound

the thing is even with the LED connector unplugged the voltage still goes from around 19v to 0v on startup. Shouldn't the voltage stay on when the connector is unplugged?

NO, the LEDs strings are parts from the circle circuit.

[budm]

Re: LG 42LB5600 standby light works but no picture and clicking sound

1) Post #2 ask about the Voltage on the main filter cap C610.
What do you get when measure the Voltage right between the two legs of the cap when TV is turned on?

2) What do you get when measure the Voltage right between the two legs of the cap C224 when TV is turned on?

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

1) Post #2 ask about the Voltage on the main filter cap C610.
What do you get when measure the Voltage right between the two legs of the cap when TV is turned on?

2) What do you get when measure the Voltage right between the two legs of the cap C224 when TV is turned on?

C610: 393v

C224: 193v

i took the panel apart only to realize i don't have a 24v power supply to test the LEDs.

[dick_barton]

Re: LG 42LB5600 standby light works but no picture and clicking sound

Are you certain that C224 reads 193V. The capacitor is rated at 160V ?

[Diah]

Re: LG 42LB5600 standby light works but no picture and clicking sound

C610: 393v

C224: 193v

i took the panel apart only to realize i don't have a 24v power supply to test the LEDs.

you can see them with eyes which one not lid.. you can record movies to see it correct as it is could for less second

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

What were the readings. Can you see the part numbers written on them?

the readings on the top one (with the arrow) was 532 (not sure of the units) on the middle and right pin.

the bottom one with the square was 180 arcoss the middle and top and also 180 across middle and bottom pins.

the part number for the top transistor is:
MD3752
F9004HGE

The bottom transistor though the hole i can read:
KMBRF20
U100CTA

[neilc6]

Re: LG 42LB5600 standby light works but no picture and clicking sound

I'll help with Diah's English translation. The TV will power on with the panel disconnected and you can watch the LEDs flash to see which one is not lighting up. You can record it on video and go frame by frame if it is too quick.

I will add with LED problems, it is better to replace all the strips with new. They all have wear and the ones still working are likely to fail. With the LB series, the heavy lenses also tend to fall off with age.

Here is a good analogy. My right side low beam burnt out on my car so I replaced it but bought a spare since I expected the left side to go as well. Sure enough, a couple of months later the left side went. My daytime running lights have more hours on them and use the same bulbs but I don't expect them to fail. Why not? Because they run dimmed around 40% of maximum. Same thing applies with LED backlights except of having 2 bulbs, you have a string of many.

[Diah]

Re: LG 42LB5600 standby light works but no picture and clicking sound

thx neilc6

[jmandawg]

Re: LG 42LB5600 standby light works but no picture and clicking sound

What were the readings. Can you see the part numbers written on them?

you can see them with eyes which one not lid.. you can record movies to see it correct as it is could for less second

i don't see any of them turn on at all.