Panasonic TH-55AS670A no picture no sound

[mar1in]

Hi everyone,

I've got this Panasonic TV here with the following symptoms:

* Standby Light is solid RED
* Turning on using the Button on the TV (long press) would change LED to blinking GREEN
* After a couple of seconds, LED is solid GREEN and without picture or sound.

I've tried a couple of things before tearing it apart:

* Resetting using various combinations of powerbutton and volume buttons pressing down while booting.
* Activating Self Check according to service manual using IR Blaster (we have no remote unfortunately)

At that point I decided to open up the back cover. Measuring the basic Testpoints I was able to find:

* All test points on the P Board seemed okay, the LED Backlight is getting 24V for each strip (6 in total)
* On the A Board all test points are fine except the 12V, which shows 0V
* I also went ahead (because I had some spare time) to tear apart more and test the LED Backlight strips using my 21V power supply, and I was able to light them up all individually (12x for 7 LED's)

That means, there must be something wrong with either the P or A board or TCON board. But at this point I'm not sure what should be my next step before I try to order and replace any of the boards.

Its a very good TV even though its almost 10 years old, would be sad to throw it into the garbage.

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

I should have mentioned that after a while (after solid GREEN LED) it goes back to standy and showing the red LED blinking code 13, which I have heard of it's related with the A or main Board.

[nomoresonys]

Re: Panasonic TH-55AS670A no picture no sound

Can you post a clear focused picture of the legend/map with expected voltages by the connector on powerboard or list it if you can't get a clear picture, check optical output/toslink port on mainboard, is it lit red?

[nomoresonys]

Re: Panasonic TH-55AS670A no picture no sound

Can also try turning on tv with one ribbon cable at a time unhooked from tcon to panel at tcon side, so do one then the other, best practice is to have tv unplugged from power while making any cable unhooks or hookups, see if there's any change in display or blinking.

[lotas]

Re: Panasonic TH-55AS670A no picture no sound

I should have mentioned that after a while (after solid GREEN LED) it goes back to standy and showing the red LED blinking code 13, which I have heard of it's related with the A or main Board.

"Shows flashing red LED with code 13" - this is a problem with the eMMC where the firmware is located.

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

Can you post a clear focused picture of the legend/map with expected voltages by the connector on powerboard or list it if you can't get a clear picture, check optical output/toslink port on mainboard, is it lit red?

not sure where to find this legend map? the toslink optical output is not lit red, so are the USB Ports also not providing any power (when connecting my google chromecast)

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

"Shows flashing red LED with code 13" - this is a problem with the eMMC where the firmware is located.

ok, sounds like this is not repairable unless i replace the whole board?

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

Can also try turning on tv with one ribbon cable at a time unhooked from tcon to panel at tcon side, so do one then the other, best practice is to have tv unplugged from power while making any cable unhooks or hookups, see if there's any change in display or blinking.

Thanks, I think I've tried that with no change. Will try again though just to be sure

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

Looks like the 13 blink code is not coming up today and it would just stay turned on (green LED solid) until it shuts down itself after a couple of mins.

There seems to be no voltage on the TCON board. No USB power, no TOSLINK red light.

What else can I try, I heard I could try to put the mainboard into the oven and bake it for 20 mins for a reflow. That would be my last attempt though

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

There is also no voltage on the SRV-12V testpoint. The other two testpoints show 5.3V and 16V each.

I took out the board for you to see maybe any obvious faults.

[nomoresonys]

Re: Panasonic TH-55AS670A no picture no sound

Maybe Lotus can tell you how to test to make sure it's eMMC problem if possible, I can not recall the procedure.

[lotas]

Re: Panasonic TH-55AS670A no picture no sound

Replacement with a new one with clean service firmware.

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

ok i think this will be out of my capabilities i'm afraid.

if i understand that correct, the software is unable to boot because of this ?

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

Can you post a clear focused picture of the legend/map with expected voltages by the connector on powerboard or list it if you can't get a clear picture, check optical output/toslink port on mainboard, is it lit red?

Sorry I think I know what you meant by now.
I've measured the following voltages on the connector of the mainboard (A Board):

Pin 1: 15.7V (16V)
Pin 2: 15.7V (16V)
Pin 3: 15.7V (16V)
Pin 4: 0 (GND)
Pin 5: 0 (GND)
Pin 6: 0 (GND)
Pin 7: 5.2V (5VS)
Pin 8: 0 (BL_ECO)
Pin 9: 3.3V (SUB_ON)
Pin 10: 3.3V (KEY)
Pin 11: 0 (BL_ON)
Pin 12: 3.3V (POWER_ON)
Pin 13: 0 (PWMA)
Pin 14: 3.3V (BL_SOS)
Pin 15: 0 (PWMB)
Pin 16 0 (PNL_3D_ON)
Pin 17: 0 (PWMC)
Pin 18: 0 (PWMD)
Pin 19: 0 (PWME
Pin 20: 0 (PWMF)
Pin 21: 0 (PWMG)
Pin 22: 0 (PWMH)

So that means I'm getting BL_SOS although I've check my LED strips individually and can confirm they are working. Must be something in between or a bad connection somewhere?

[nomoresonys]

Re: Panasonic TH-55AS670A no picture no sound

Maybe you could slip the BL_SOS wire off and put it on one of the empty ground spots, there's a little tab you can lift to free it from the connector, I use a flat head screwdriver from a mini precision set, then try it. This is just a test.

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

Maybe you could slip the BL_SOS wire off and put it on one of the empty ground spots, there's a little tab you can lift to free it from the connector, I use a flat head screwdriver from a mini precision set, then try it. This is just a test.

good idea, i was actually thinking of doing something like that just to see if the backlights would come up for example. in this case should they come up or is it to test the mainboard to see if it succeeds booting up?

[nomoresonys]

Re: Panasonic TH-55AS670A no picture no sound

I think it's a bypass, which if the tv starts working then it has to do with a problem somewhere in the backlight circuit, which can mean bad leds or a connection etc.

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

I think it's a bypass, which if the tv starts working then it has to do with a problem somewhere in the backlight circuit, which can mean bad leds or a connection etc.

just tried but did not change anything. still the same symptoms
i'm not getting the 13 blink code anymore, either way (with or with unplugged BL_SOS pin), it just shuts down after a few mins as it seems to be not getting any input and the red led is on solid (not blinking)

[nomoresonys]

Re: Panasonic TH-55AS670A no picture no sound

I see, ok prolly a bad eMMC as suggested by Lotus.

[mar1in]

Re: Panasonic TH-55AS670A no picture no sound

is there any way to reflash via USB ?