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Old 12-12-2017, 02:31 PM   #1
WTRWLKR
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Default LG 60LB5200 will not turn on

LG 60LB5200 will not turn on. There is a green standby light.

Measured voltages at the power supply output connector. All 12V pins were at 7V. All 24V pins were at 15.5V. EN pin is at 2.2V

Does this appear to be a faulty power supply or is there something else I need to look at?
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Old 12-12-2017, 03:30 PM   #2
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Default Re: LG 60LB5200 will not turn on

Are you happy your dmm is reading correctly ? Then measure voltage across the two largest caps - neg on lhs pin pos on rhs pin - should get 350/400v.
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Old 12-12-2017, 06:16 PM   #3
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Default Re: LG 60LB5200 will not turn on

To be safe, I used a different meter. Voltages were much the same.

Here are the actual voyltages, instead of my memory.

12V = 6.95V
24V = 15.64V
EN = 2.54V

Both of the large caps are 163.2 VDC
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Old 12-12-2017, 06:25 PM   #4
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Default Re: LG 60LB5200 will not turn on

Your PFC Voltage booster is not working.
Check the RESISTANCE of the Diode D12 in both direction.
We also need good clear picture of the bottom side of the board.
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Old 12-12-2017, 06:49 PM   #5
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Default Re: LG 60LB5200 will not turn on

Do I need to remove D12 from the board, before testing it?

Power removed, D12 still on the board
Negative on cathode: 30k or 239k (it changes between them)
Positive on the cathode: started at 250k and climbed to over 1M, before I stopped measuring it.
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Old 12-15-2017, 08:21 AM   #6
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Default Re: LG 60LB5200 will not turn on

I guess I must have stumped the veteran members with this one. It's been about 30 years, since I last dealt with electronics at this level.
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Old 12-15-2017, 10:45 AM   #7
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Default Re: LG 60LB5200 will not turn on

OK, PFC diode is OK.
Get the P/N as printed on the U1 SMD IC and then look up the spec sheet so you can find out which pin of the IC is the VCC pin so you can verify if the IC is getting the power to run it or not when the TV is turned on.
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Old 12-15-2017, 08:14 PM   #8
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Default Re: LG 60LB5200 will not turn on

Looks like an NXP TEA1755T

Pin 1 Vcc = 1.15V
Pin 5 LATCH = 1.10V
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Old 12-21-2017, 04:24 PM   #9
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Default Re: LG 60LB5200 will not turn on

Is the Vcc good or bad? Do you need me to get other voltages?

Thanks for your guidance.
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Old 12-21-2017, 05:00 PM   #10
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Default Re: LG 60LB5200 will not turn on

Service manual at manualslib may help with diagnosis. It is slightly different model but PSU may be much the same.
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Old 12-21-2017, 07:06 PM   #11
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Default Re: LG 60LB5200 will not turn on

Quote:
Originally Posted by WTRWLKR View Post
Looks like an NXP TEA1755T

Pin 1 Vcc = 1.15V
Pin 5 LATCH = 1.10V
It is not getting way too low of the Voltage to run, so the next thing will be tracing out the VCC pin back to switched Transistor on that power supply board to see if it is getting the Voltage feeding it and the control Voltage to turn it on or not. This is not going to be easy for beginner unless you are really good at tracing out the board.
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Old 12-22-2017, 08:00 AM   #12
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Default Re: LG 60LB5200 will not turn on

I was able to trace Vcc to a nearby transistor. Is it the one you are needing voltages from, or did I miss it by a long shot?
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Old 12-22-2017, 08:33 AM   #13
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Default Re: LG 60LB5200 will not turn on

maxvalutech, I looked at the manual. It appears to get into everything except the power board.

The only reference that I found for the power board was a statement of if power on voltage is not 3.5V, replace the power board.
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Old 12-22-2017, 01:15 PM   #14
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Default Re: LG 60LB5200 will not turn on

Page 27 of sm gives a bit of circuitry for 3.3 vcc
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Old 12-22-2017, 03:29 PM   #15
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Default Re: LG 60LB5200 will not turn on

What DC Voltage do get between the two legs of the cap I circle in red?
The Voltage on that cap is generated from the AUX winding of the STBY Transformer.
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Old 12-26-2017, 06:31 PM   #16
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Default Re: LG 60LB5200 will not turn on

I hope everyone had a great Christmas.

I think I used a bad ground point for Vcc. Using PIN 1 for Vcc and PIN 2 for ground, I get 14.49V.

I measured across the cap and get 15.1V.
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Old 01-11-2018, 11:55 AM   #17
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Default Re: LG 60LB5200 will not turn on

Are these the expected voltages?

What voltages should I look at next?

Thank you
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Old 01-18-2018, 10:16 AM   #18
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Default Re: LG 60LB5200 will not turn on

Have I stumped the experts?
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Old 01-18-2018, 10:39 AM   #19
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Default Re: LG 60LB5200 will not turn on

So the IC is getting the VCC to run but it is not running.
Report the other pins Voltages too to see if they are what they should be or not, make sure to use good GND this time.

Last edited by budm; 01-18-2018 at 10:41 AM..
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Old 01-18-2018, 11:01 AM   #20
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Default Re: LG 60LB5200 will not turn on

Got it. I will use Pin 2 for the ground point and record the voltages of all other pins.

I will do that after I get home tonight and post the results.
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