SHARP LC-46LE730E - no backlight, no picture, no sound

[Davi.p]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Budm it says that on first power on seconds the panel VCC jumps to 12v then shuts down, therefore Panel-on will be High for the same time.

[CMG97]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

I am a little confused. What do you have on PANEL_ON pin when you toggle TV on and off? You show 0V on post #17.

I will use the notations used on the wiring diagram.

So after I hit the Power button the PANEL_VCC jumps to 12V (actually it's less after my multimeter shows a value) and then immediately it starts to decreasing slowly. This is a transient state.

The values shown on the diagram were my readings after powering on the TV and waiting for a few mins.

On PANEL_ON_P1 I cannot get a proper reading, since I don't have an oscilloscope. My multimeter only shows a sec hesitation and the 0 V after turning on the TV. So my theory is that the software opens the PANEL_VCC (by turning PANEL_ON_P1 on) for a very little time, and recognizes that something is not right and shuts it down. But after all, it is just a theory.

The FET301 seems to be faulty anyway, I don't really have any other idea why the software doesn't give the 12V power to the PANEL_VCC, but replacing the FET301 worth a try.

[CMG97]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Update:
I desoldered the FET301 component. Sad news. The voltage drop I measured was the voltage drop through the board (It was very close to 0 V but not exactly 0 V. I can reproduce the same numbers through measuring the pins on the board without the FET).

The FET is fine in my opinion:

S1-D1: 0.546 V
D1-S1: open loop
S2-D2: 0.545 V
D2-S2: open loop

I will change it anyway, but I'm pretty sure this won't solve the problem. I'm out of ideas for now. If you have any suggestions please feel free to share them with me.

Also, according to the service manual the 542E uses the YA version of the T-CON board in case of 40 inch TVs and YB in case of 46 inch TVs. Mine was equipped originally with the YB version. Mainboard is the same in both cases. So I think in this case the cause of the problem isn't the incompatibility between the mainboard and the T-CON.

[Davi.p]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

S1-D1: 0.546 V

You previously said 0,049v
anyway can you confirm the FT301 pads connections? I think S1>GND; D1>S2; D2>12VCC-in.
You are probably measuring a diode or transistor but i don't know which one..

[nomoresonys]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Check D901.

[CMG97]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

It was 0.049 V when the FET was soldered in. I desoldered it and measured it alone. (The voltage drop between the pads are 0.045 V/0.066 V now. )

The voltage drop between the FET pins (FET desoldered) are the ones I wrote above.

I can confirm the connections you mentioned.
D2: 12VCC (PANEL_VCC)
S1: GND
D1 is connected to S2

I will try to follow back the route of the D1 pad to find a diode or transistor. Sadly I don't have a schematic for the T-CON.

Edit:
I only saw nomoresonys's post after publishing mine. I'm looking for D901.

[nomoresonys]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

It's on the powerboard.

[nomoresonys]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Also check D902, D906 and D907 all are on powerboard.

[CMG97]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Voltage drops:

D901:
One way-0.457V
Other way-Open loop
D902:
One way-0.459V
Other way-Open loop
D906:
One way-0.462V
Other way-Open loop
D907:
One way-0.564V
Other way-Open loop

They all seem fine to me.
I'm not sure whether these diodes are related to the backlight or not, but I can turn on the backlights manually by shorting the PS_ON and BS_ON pins and it turns on fine. (Software won't set the BS_ON pin high, so that's the reason for the lack of backlight.)

I will upload a high res edited pic of the T-CON soon. Probably I found the cause of the 0.0.. V voltage drops, but can't identify the SMD components.

[Davi.p]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Ok i thought in post 23 you were measuring pads, but the switching supply that includes fet301 outputs 1v for the processor core, since it draws much current the diode test returns a low value that seems a short but maybe it is not, by measuring on D1-S1 pads you're measuring the supply output, if you feed 1v to the coil connected to S2 you are feeding the processor and you can notice if there is a short but i think much probably the fet301 is bad. Please test in ohm S1-D1

[nomoresonys]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Ok, they look good, sometimes a bad one will give similar symptoms.

[nomoresonys]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

So did you say that both mainboards have the same numbers on the white sticker, it's the bigger white one.

[CMG97]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Okay, so I changed the FET, and the TV is still dead.
S1-D1 pads resistance: 89 Ohm in one direction and 100 Ohm in the other. You were right, it isn't the problem. After I changed the FET I didn't power up the T-CON with a PSU to check the voltages because I didn't want to mess with it yet.

So I went back to the IC9701. I could cause the same backlight turning on thing than previously. (touching the IC and sometimes the backlight started to blinking real fast, and sometimes turned on for a few secs (like a contact problem)). It turned out that I was just shorting something with my finger and it turned off the power of the FRC and when the FRC was off the backlight went on. (IC9701 powers the FRC chip) Also the 12 V power to the T-CON appeared when the FRC was out. I checked the power to the FRC, it is stable 1.1V as it should be so there is no problem on power side to the FRC.

So I think it is clear that the FRC shuts down the T-CON on purpose, I'm just not sure why. I found an YB version T-CON nearby for a fair price, I will buy it and try if it works.

Sadly I cannot work on the TV for the next 4 days.

I would like to thank you for your help so far. I really appreciate it! If you have any further ideas about the cause of the problem please don't hesitate to write it!

[nomoresonys]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Good testing video there, maybe check the voltage regulators on the mainboard: https://www.youtube.com/watch?v=ocqnqmBxiqY

[Davi.p]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

Sad, so probably your original fault was the mainboard, maybe a partially erased spi flash connected to the FRC, if you dont have a simple programmer like CH431A you will not find this. So now with original m.b. you can test a short 12v pulse on the PanelVcc rail?

[kas49]

Re: SHARP LC-46LE730E - no backlight, no picture, no sound

For reference

I had the same problems:
- no sound no, no picture, no backlight
- all voltages are OK except BL_ON: 0V
- backlight turns on when BL_ON bridged to 5V

Look here
https://www.apreslachat.com/forum/SH...2124213/271744
here
https://alpengeist-tvrepair.blogspot...g-bricked.html
here
https://www.badcaps.net/forum/showthread.php?t=60900
and here
https://www.sharp.de/cps/rde/xchg/de...&lang=de&cat=0

Been there, done that, and guess what ?? it works!!

Hope it will help future lurkers