LG 55LS4500 No Standby light will not power on

[RFITTS46]

Original owner, several years ago lost audio but used analog outputs.
No other problems and currently has no standby light and will not power on.
The Pwr On (3.5V signal back from main brd) is erratic, sometimes there sometimes not. sometimes when connected to mains it is there and 12V and 24V present and across the big caps 380V present. There is a green LED on psu board and it sometimes blinks 5 times repetively.

Sometimes when connected to mains no 3.5V Pwr On from main board. The 2X 3.5V present from psu board but no 12V or 24V and it reads 179V across the big main caps.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

when mains connected and no Pwr On present from control board....jumpered 3.5V Std By and the psu board seems to have all voltages present. the big filter caps have 380V across them. I measured 56V leaving the top of the psu board P201 and P203. this must be supplying the LED strips? the board has marked on 78V?

just looked at what was marked on the board for Pwr On (P201) and it has 24V. Is this the signal sent back from the control board and it should be 24V and not 3.5V?

[diif]

Re: LG 55LS4500 No Standby light will not power on

Start on page 13, troubleshooting.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

3.5V present P403 pin 9
3.5V present Micom Voltage

measure X201 clock
will Fluke 83 be able to measure 24mhz?
If so this is a two leaded component assume one probe on each should read 24mhz?

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

okay looks like the Fluke max's out at 200khz. I have an analog 20mhz oscilloscope?

[R_J]

Re: LG 55LS4500 No Standby light will not power on

just looked at what was marked on the board for Pwr On (P201) and it has 24V. Is this the signal sent back from the control board and it should be 24V and not 3.5V?

There are two rows of pins on P201
pin #1 = PWR-ON
pin #2 = 24v
pin #3 = 24v
pin #4 = 24v
pin #5 ~8= GND
pin #9~12 = 3.5v (standby)
etc.
Shopjimmy does have a few eeprom's for this model, that might be the problem. If you do order one make sure you get the correct one for your board.

[budm]

Re: LG 55LS4500 No Standby light will not power on

At this point we need to know what the Voltages are for all the pins of the power supply connector that goes to the main board when TV is off and when power switch is activated.
We also need pictures of the whole back side of the TV showing all the boards so we can see what we are dealing with.
"Pwr On (P201) and it has 24V"
Based on that, Please make sure to count or inspect the pin names and numbers correctly, the connector has Odd and Even number columns.

[budm]

Re: LG 55LS4500 No Standby light will not power on

BTW, is this your power supply board?
https://www.shopjimmy.com/lg-eay6251...-led-board.htm

Other boards:
https://www.shopjimmy.com/catalogsea...?q=LG+55LS4500

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

P201 on powers supply board, Mains Connected, no standby light on
P-Dim2 .04
12V .04
12V .04
12V .04
GND 0
GND 0
3.5V 3.5
3.5V 3.5
GND 0
GND 0
PWR ON 0


pressing power on .....no change
I jumpered 3.5V to PWR ON before I realized it was supposed to be 24V
jumpering 3.5V all voltages present. 380V on large filter caps

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

sometimes when mains are connected the 12V, 24V, and across big filter caps 380V is present. The yellow led blinks 5 times repetitively.

when this occurs there is no standby light.

it isn't doing it right now.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

when jumpering 3.5V to Pwr On the LED strip voltage is 56V. Seems low should be 78V.

[budm]

Re: LG 55LS4500 No Standby light will not power on

It also need DRV-ON (BL-ON) for backlights circuit to come on, sometime the Dim control pin may also need to be forced on too.
When performing force on you must disconnect the cable going back to the main board first otherwise you can damage the main board, it should also be done using resistors in case wrong connection is made.
BTW, you did not report all the pins' Voltages of P201.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

budm..

P201 on powers supply board, Mains Connected, no standby light on
jumper 3.5V to Pwr On

P-Dim2- 3.5
12V- 12.2
12V- 12.2
12V- 12.2
GND- 0
GND- 0
3.5V- 3.5
3.5V- 3.5
GND- 0
GND- 0
24V - 24.8
PWR ON 3.5
where the LED voltage is only 56V could it be booster circuit?

[budm]

Re: LG 55LS4500 No Standby light will not power on

Again, you only report the Odd column (Exposed pins you can see from the top side of the board). The Even column you have to use skinny probe on the wire entrance side of the connector.
See the printed chart for pins right next to the connector, as you can see, it has lots more pins than what you are reporting, you can see the DRV_ON (BL-ON) pin and other pins as well listed for the Even column.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

P201 on power supply board, Mains Connected, no standby light on
P-Dim2 .04
12V .04
12V .04
12V .04
GND 0
GND 0
3.5V 3.5
3.5V 3.5
GND 0
GND 0
24V 0
PER ON 0

ERROR 0
P-Dim .139
N.C .015
DRV-ON .124
VSYNCH-IN 0
GND 0
3.5V 3.5
3.5V 3.5
GND 0
GND 0
24V 0
24V .017

PUSHING PWR ON SWITCH NO DIFFERENCE

[nomoresonys]

Re: LG 55LS4500 No Standby light will not power on

If you're properly jump starting the powerboard by itself and your voltages are not coming up to specs., I'm thinking you have a powerboard issue.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

last set of posted P201measurements were taken without jumping 3.5V to Pwr On pin because budm said something about properly jumping the psu board. awaiting proper jumping instructions so no damage is incurred to control board.

earlier threads show proper power supply measurements evident when jumping 3.5V to P201 Pwr On pin.

budm wanted the second row of P201 pins measured.

I thought it maybe best to post non jumpered measurements first.
If it is requested to jumper and provide measurements of second row of P201 will do so.

[RFITTS46]

Re: LG 55LS4500 No Standby light will not power on

last set of posted P201measurements were taken without jumping 3.5V to Pwr On pin because budm said something about properly jumping the psu board. awaiting proper jumping instructions so no damage is incurred to control board.

earlier threads show proper power supply measurements evident when jumping 3.5V to P201 Pwr On pin.

budm wanted the second row of P201 pins measured.

I thought it maybe best to post non jumpered measurements first.
If it is requested to jumper and provide measurements of second row of P201 will do so.

[Andrew F. Ali]

Re: LG 55LS4500 No Standby light will not power on

This sounds like a bad backlight issue. He doesn't seem to understand what budm is saying and asking. If you jumped the Std-by 3.5V to the PWR-ON and getting the 12V and 24V. He should leave that jumper in place and make another jumper from 3.5V to DRV-ON. With the Backlights connected. The backlights should com on and stay on if they are good.

[budm]

Re: LG 55LS4500 No Standby light will not power on

Testing power supply/backlights circuits:
1) TV is not plugged into AC outlet. Disconnect the cable between power supply board and the main board, leaving everything else connected.
2) Put resistor (any value between 330 ~ 1000 Ohms 1/4 W or what ever you have) between 3.5V pin and PWR-ON pin.
3) Put resistor (any value between 330 ~ 1000 Ohms 1/4 W or what ever you have) between 3.5V pin and DRV-ON pin.
4) Plug TV into the AC outlet, the backlights should then come on and stay on as long as the AC is being applied to the TV. If the backlights still do not come on then we may have to use another resistor on the Dim control pin, but try the test first to see what happen.
But based on your report (all boards connected) that the PWR-ON pin Voltage does not change state when power switch is toggle, it means you have problem on the main board.