Sharp LC-46D85UN works for 2 minutes shuts down with a pop

[advant]

I am hoping somebody can help me out with an issue with my Sharp LC-46D85UN LCD TV which is nearly 10 years old.

Here are the symptoms:

--Turns on normally, stays on for around 2-5 minutes, picture disappears with a pop from the right speaker.
--Backlight stays on, power LEDs both stay on, no blinking. Remote is not responsive when it is in this state.
--Power button on TV is not responsive for single press. If I hold it long enough, the TV will shutdown.
--The TV will turn back on again either with the remote or with the power button on the TV and will be normal for 2-5 minutes and the process repeats.
--If I don't shut the TV down by holding the power button down, the pop repeats after a few seconds. Pop on the right speaker, then pop on the left speaker and a few seconds later a "swish" on the right speaker and later a "swish" on the left speaker. This will keep repeating until I turn the TV off holding the power button.
--There was also one time (only once) when I was using the component cable that I heard a loud beep coming from the speakers, the video was intact but no sound. TV was not responsive to the remote.
--There have a couple of times, I got this to happen with the TV showing white/green vertical lines. You could see the video behind the lines. Remote again was not responsive.

The power board of the TV was replaced around 5 years back when it falied. I have taken out the power board and verified that all voltages are correct. I actually have two power boards, one that is on the TV now and the old one that I replaced the standby IC (TNY264PN) on. Both power boards check out fine. So I suspect it is not the issue with the power board.

Initial suspicion was with the BU3.3V that is generated out of the main board from the BU5V fed to it by the power board. The fact that the power LEDs stay on leads me to believe that BU3.3 V is available although I have not probed the main board.

I am attaching pictures of the main board. Is there an issue with the main board or the TCON board?

[CapLeaker]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

sounds like a bad main board to me. Just the fact that the TV shuts off after it ran for a few minutes, tells me that the problem is very likely an IC.

[advant]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

Thanks for the input. I plan to open the TV up again and probe the main board for power supply values coming out of the regulator. Is there anything else I should be looking at? I am not able to make too much sense of the small red flashing LED in the middle of the main board. Does that indicate something?

[nomoresonys]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

Good video there, testing voltage regulators etc: https://www.youtube.com/watch?v=ocqnqmBxiqY

[advant]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

Thanks. Will check out the video.

Here is an update. Probed PD connector at the main board after the TV hangs up. Here are the values:
Pin--Name--Value
PD1--13.5V --12.81 V
PD2--13.5V --12.81 V
PD3--13.5V --12.82 V
PD4--13.5V --12.81 V
PD5--SGND-- 0 V
PD6--SGND-- 0 V
PD7--SGND-- 0 V
PD8--SGND-- 0 V
PD9--AC_DET--2.98 V
PD10--PS_ON--2.81 V
PD11--BUS5V--4.94 V
PD12--PNL_POW 3.14 V

These values look normal, don't they?

There is a small red LED on the main board. I have now determined that if the red LED flashes 2 secs ON 1 sec OFF, the TV is fine and has not hung. When it hangs, the red LED stays ON without flashing. Does that offer a clue?

I am attaching a snapshot of the main board schematic showing this LED.

[CapLeaker]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

The panel power should be higher than 3.14V. Check that again, when the TV works vs non working.

[budm]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

You can verify if the PNL_POW signal is OK or not by checking the PNL-12V that goes to the T-CON board, if 12V is there then the PNL_POW is fine.
Can we see the pictures of the whole backside of the TV showing all the board?
What is the power supply board P/N?

[advant]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

Here is an update:

Probed PNL_POW when TV is working and when it is hung. Both read 3.14 V. No difference at all. Also, probed the PNL12V pin on the power board per budm's suggestion. I read 11.94 V regardless of whether the TV was working or not.

I am attaching pictures of the whole backside of the TV including individual pictures of each board. The part # of the power board is RDENCA336WJQZ.

These pictures were taken when the TV was in a hung state. You can see the backlight on through the holes in the back. You can also see the red LED on the main board that I was earlier referring to. It is not flashing. It is static ON. Also, you will see that the speaker connector disconnected in these pictures from the main board. This is because the TV was making a very loud noise (much like white noise) when it was hanging.

I also probed the power supply side of the 1K resistor that is connected in series with this LED. The power supply is marked D3.3V and it read exactly 3.29 V regardless of whether the TV was working or not.

I have also tried to disconnect one connector after another on the main board and can confirm that the TV hangs even with most of them removed (I left the key module and R/C LED module on but disconnected them separately to make sure they were not causing anything). So it does look like it is pointing to the main board at this point, doesn't it?

I am hoping its is not an IC issue as replacement main boards are hard to find. Next, I plan to flip the main board and probe all the power supplies the main board generates to see if I can find something there. Any suggestions on what to look for are very much appreciated. Thanks a bunch.

[budwich]

Re: Sharp LC-46D85UN works for 2 minutes shuts down with a pop

you can try reloading the firmware just in case it got corrupted.