Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

[BookWormStud]

I bought Panasonic Viera TH-L50B6D Led TV 3 years ago. Last night when I turned it on the screen started flickering (like quickly turning on and off but I could still see the HDMi header on top left). It did that for 9-10 seconds and then went to stand by with red light blinking (I counted to 20 times but it was still going). I connected the set top box with TV and turned on earlier than TV, it plays video and audio but with screen flickering (turning on and off)

I disconnected the Backlight and did the flashlight test and the LED panel works fine and shows menu and stuff. But with backlight flickering it seems like it turning on and off.


After reading few threads here which suggested to reduce my Backlight & Brightness setting in menu. I did that and now TV screen keeps on flickering but the TV doesn't go to standby even being left ON for 15 minutes. But as soon as I try to access the USB option on TV (which uses the cranked up Backlight & Brightness settings and doesn't use TV's default setting) it goes to stand by like this ---> https://youtu.be/k_luFw1g_fU

• Multimeter I'm using
• Main Board
• Power Board
• Inverter Board
• Overall connection

I don't have the voltage schematics for any board on TV. I checked the Input voltages of Inverter Board (10 pin with 9 wires connection) and Backlight (7pin connector)

Few voltages I have read with this multimeter (please refer to this image before seeing the below voltages)

Input Voltage of Inverter Board (10 pin with 9 wires)

Output Voltage of Inverter Board or Input to Backlight (7 pin connector)
Here with cable means Backlight cable is attached and vice versa.


Some Important Points:

1. Keeping the TV in normal TV/AV mode, it doesn't go to standby. Also disconnecting the Inverter board from Power Board will send the TV to standby after keeping it ON for sometime.
   
   
2. Disconnecting the Backlights from Inverter board doesn't send the TV to standby. (and backlight is off)
   
   
3. Disconnecting the Main board from Power board doesn't show any sign of power. But I used the multimeter to check. It gives a stable voltage of around 10-12 mV at 7pin connection of Backlight & Inverter Board (at some pins not all, if you'll ask I can recheck & post all the voltages).

Anything you want regarding voltages just tell me which connector and Standby or ON, I'll get it for you.

Thanks,
BWS

[BookWormStud]

[UPDATED] Panasonic LED 1 Blink Code

Hello,

Some of you may have read my earlier post about Panasonic Viera TH-L50B6D.

TL;DR Backlights turning ON and OFF. LED screen is alright did the flash light test. After sometime TV goes to standby with Red Light Blinking. Reduced brightness, now TV stays ON but backlight turning ON & OFF.

[UPDATE] Someone on reddit provided me with the Service Manual (don't download I'll provide important images later) of TV almost similar to that of my TV. Only difference is Main/A-Board (that too in position of connections everything else is same).

Take a look at these:

Overall Schematic

Wiring Diagram

Block Diagram 1 A-Board

Block Diagram 2 Other Boards


Now I'm asking, Is there any way to jump the wires with A/Main-Board disconnected from P/Power Board and turn ON the backlights.

I'm not asking this from the back of my head, I read it somewhere and couldn't understand what to do. Here's the Post

Thanks. Any other Info you need please comment.

[tom66]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

I have merged this post with your current thread; please do not create duplicate threads for the same issue.

[BookWormStud]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

I have merged this post with your current thread; please do not create duplicate threads for the same issue.

Thank You.

You're the first person to reply.

[Moreno83]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

Well , it is either a bad power supply or bad leds. I would say 1 or more leds are failing , leds are giving voltage back. When you higher the brightness ( voltage ) the leds don't give the correct voltages back which causes the shutdown/flickering....

You need to look at the leds under the LCD and see if notice any burning etc....

[dick_barton]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

Looking at the voltage readings you give for the Led Driver board I suspect that you have a led or leds which are starting to fail.

Leds connected
Pin1, Led1, 88V
Pin2, No connection
Pin3, Anode 1, 175V
Pin4, No connection
Pin5, Led2, 15V
Pin6, No connection
Pin7, Anode 2, 85V

With the Leds disconnected both Led Anode1 & 2 are at 170V which is good.


You need to remove the panel carefully and check all the leds since it does appear that one or more are starting to fail.

[BookWormStud]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

Looking at the voltage readings you give for the Led Driver board I suspect that you have a led or leds which are starting to fail.

Leds connected
Pin1, Led1, 88V
Pin2, No connection
Pin3, Anode 1, 175V
Pin4, No connection
Pin5, Led2, 15V
Pin6, No connection
Pin7, Anode 2, 85V

With the Leds disconnected both Led Anode1 & 2 are at 170V which is good.


You need to remove the panel carefully and check all the leds since it does appear that one or more are starting to fail.

1. Attachment TV.DOC file has some voltages I've checked maybe this would help. About opening the panel, I'm keeping that card as last resort.

2. Since BL_SOS voltage is all over the place I thought maybe that is causing the problem. So, my first guess was that If LED(Back lights) are bad then they are triggering the BL_SOS fluctuation, so I disconnected the LD3 connector. But the BL_SOS was same (fluctuating). Then I disconnected the LD1 connector which stabilized the BL_SOS voltage to 3V. I don't know if this signify anything please enlighten me on this.

3. Also I read Budm's CFL Inverter Tester Thread, can it be applied to this case.

[BookWormStud]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

Well , it is either a bad power supply or bad leds. I would say 1 or more leds are failing , leds are giving voltage back. When you higher the brightness ( voltage ) the leds don't give the correct voltages back which causes the shutdown/flickering....

You need to look at the leds under the LCD and see if notice any burning etc....

Please read post #7

[Andrew F. Ali]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

Strip down the panel and get to the LEDs...If you cant determine the 'bad' LEDs....replace the entire strip/s....If you have spare LEDs and can find the defective ones then you could probably use the reeceyburger stack method and have your set working again.

[dick_barton]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

I tend to agree with Andrew.
The open circuit led voltage is 170V which appears to be OK since the capacitors on the led output line is 160V and 250V.
The SOS signal would be an "error signal" being fed back to indicate a led(s) fault.
The manual also seems to indicate that this should show up by the standby led flashing once every 4 seconds.

[BookWormStud]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

So everybody here is telling me it's the Backlight problem. Since I have zero XP in repairing TVs that's why I'm trying to figure if the problem is something else.
Thanks for the help.

Since Panasonic's Service center don't replace or provide Backlight, I think I'm gonna have to do it myself.

Before I go and try to replace Backlights, I just have few more questions.

If you'll look at voltage chart I provided in Post #7 (Specifically LD3 Connector) you'll notice there are 2 of them, one with Backlight connected and other without. With Backlight connected you'll see a voltage difference at LED1 & LED 2, But all the pins LED1, ANODE1, LED2 & ANODE2 fluctuate in a same pattern as backlight flash.(high value when LED are lit then drops to lower value then repeats cycle).

Now Question:
1. If I remove the Backlight from LD-Board the voltages at the LD3 still fluctuate in same pattern as the above. If backlights are the problem why is my LD-Board behaving like that?

2. Is there a way to troubleshoot the components of the LD-Board

[dick_barton]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

With the mainboard disconnected use a 1K resistor and jump it from 5VS to BL_ON and a second 1K resistor and jump it from 5VS to Power_ON

[BookWormStud]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

With the mainboard disconnected use a 1K resistor and jump it from 5VS to BL_ON and a second 1K resistor and jump it from 5VS to Power_ON

I have tried that but instead of using 1K Ohm resistor I used a 100 Ohm one and made the circuit like in image, nothing happens.

I'll try what you said but I have don't 1K ohm resistor with me right now. Will report back tomorrow.

[dick_barton]

Re: Panasonic TH-L50B6D screen flickering, goes to standby, red light blinking

Looking again at the schematic diagram it looks as though it's 5VS jumped to BL_ON using a 1K resistor and also 5VS jumped to Sub_On again with a second 1K resistor to bring up the voltages.