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

[CMG97]

Hey everyone!

Initially, my TV didn't want to start up sometimes and had to restart several times to have a picture and start up. One day it stopped completely and would not start since then. If I press the turn on button the blue led starts to light and after 30-60 secs (didn't measure it) it turns off completely. Except if I start it in service mode(plugging it in while holding input + vol-), because in this case it won't turn off unless I press the power button.

I started with observing the power board and everything seemed to be fine. I checked all the voltages on the connectors and everything was correct except the backlight enable pin. So I shorted the BL_EN with the PS_ON (booth 3.3 V logic if I remember correctly) and the backlight turned on without a problem.

I then moved to the main board. I touched an IC and the backlight suddenly started to turn on and off quickly (no picture still) and I thought maybe it's faulty or has contact problem. So I replaced it (IC9701) but the symptoms were the same as before. (Probably I opened the MOSFET with my finger due to electrostatic charge)

I still thought it was a mainboard problem, but I couldn't find a new mainboard for this TV. One day a similar (QPWBXF915WJN2) board appeared in Germany but not for this TV, it was for an LE542E. I checked that it uses the same T-CON board as my TV. The difference between these two are the chips. Mine uses ZR39691HGCG while the LE542E uses ZR39690HGCG. (FRC: ZR39300BGCG vs ZR39301BGCG) I think the only difference between the two are that the 39691 has 3D support which I frankly don't need.

So I thought it's not that expensive, and ordered it. After I installed it, the TV was capable of powering up and I could turn it on/off using the main power button but I still couldn't produce any sound. (I plugged in a PS4 and tried to rotate through the sources but no sound and no backlight) The FRC and CPU chips are hot with both mainboards. Sadly I don't have an oscilloscope to check if they send signal towards the T-CON board.

The T-CON board is dead cold with both motherboards.

So now I'm in bit of a trouble. I can't say for sure that the motherboard is fine, since the motherboard isn't for this TV. I think it should work with the same T-CON board, but it is possible that I'm missing something here and my TV won't power up with a LE542E motherboard even though all the connectors are the same.

My suspicion is that the T-CON board is dead and these mainboards have a check signal if the T-CON board is fine and powered up so the lack of this confirmation signal is causing the mainboards to not power up the TV properly. But frankly I'm only a mechanical engineer and my knowledge on TVs is limited.

So I ended up here hoping that someone could help me out.
Thanks for all your help in advance!

[nomoresonys]

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

Upload some good straight on clear pictures of all the individual boards and one of the whole back to see how they are connected, with all original boards in do test #3 below, try to do it just as instructed.

[Davi.p]

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

your bad tcon suspicion is probably good, you must check the service manual to compare status led blinkings to the table..

[CMG97]

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

Thank you for your answers!

I can make pics with higher resolution if needed.

Original mainboard:


New mainboard from an LE542E:




PS board:


T-CON board:



Overall pic:



Pins on PS-board:




So, I checked the voltages with both mainboards:

With original:
DIM - 3.21 V (On) - 0 V (Off)
PWM1 - 3.23 V (On) - 0.46 V (Off)
PWM2 - 3.23 V (On) - 0.46 V (Off)
BL_ON - 0 V (On) - 0 V (Off)
PS_ON - 3.36 V (On) - 0 V (Off)
GND - 0 V (On) - 0 V (Off)
GND - 0 V (On) - 0 V (Off)
5.75V- 5.83 V (On) - 0.21 V (Off)
5.75V - 5.82 V (On) - 0.18 V (Off)
GND - 0 V (On) - 0 V (Off)
GND - 0 V (On) - 0 V (Off)
12V - 12.11 V (On) - 0 V (Off)
12V - 12.11 V (On) - 0 V (Off)
5V - 5.05 V (On) - 5.24 V (Off)

With new mainboard:
DIM - 3.20 V (On) - 0 V (Off)
PWM1 - 3.22 V (On) - 0.46 V (Off)
PWM2 - 3.22 V (On) - 0.46 V (Off)
BL_ON - 0 V (On) - 0 V (Off)
PS_ON - 3.35 V (On) - 0 V (Off)
GND - 0 V (On) - 0 V (Off)
GND - 0 V (On) - 0 V (Off)
5.75V- 5.81 V (On) - 0.18 V (Off)
5.75V - 5.81 V (On) - 0.15 V (Off)
GND - 0 V (On) - 0 V (Off)
GND - 0 V (On) - 0 V (Off)
12V - 12.11 V (On) - 0 V (Off)
12V - 12.11 V (On) - 0 V (Off)
5V - 5.04 V (On) - 5.25 V (Off)

I must add, that the TV automatically turned on after plugging it in, and I could turn it off with the power button. (Previously it turned itself off after a while, but not this time)

But I noticed something I didn't notice before. After I turned the TV off (with original mainboard) the 5v and PWM voltages disappeared sometimes and I couldn't turn it back on with the power button. The only way I could start it up again was unplugging it and plugging it back again. It does not happen all the time, only a few times.

With the LE542E mainboard everything seemed to be fine and I could restart it and start it again multiple times without any problem.

Regarding led blinkings. I'm not sure if this TV does any LED blinkings to provide information. (Well actually I think it doesn't)

Here is a manual I found on the web:
https://gofile.io/?c=fzp5Nm

[budm]

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

"GND - 5.05 V (On) - 5.24 V (Off)"
You need to verify your readings, 5.05V on GND pin?

"BL_ON - 0 V (On) - 0 V (Off)" You also do not have Backlights on control signal.

[CMG97]

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

"GND - 5.05 V (On) - 5.24 V (Off)"
You need to verify your readings, 5.05V on GND pin?

"BL_ON - 0 V (On) - 0 V (Off)" You also do not have Backlights on control signal.

Thank you, I forgot to change the last line after pasting it. I edited the post, so now it’s correct. The mainboard doesn’t send backlight on signal. The only way I can turn the backlight on is by shorting it with the PS_ON pin. In this case the backlight turns on, but no picture on the screen.

[nomoresonys]

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

I'm thinking both mainboards are problematic, bad bga or eeprom maybe?? Suppose it could be the tcon but usually you still have sound when tcon is bad, right?

[Davi.p]

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

Hi, well i have recognized the tcon, it's the same of the two LC-46LE630E that i have fixed, them have a common fault in the chip FET301 on the tcon, i think much probably is your problem, in my case this little beast used to go shorted only in intermittent cases, its a dual power mosfet, when i am on the bench pc i tell you the part with whom i have substituted as a compatible, the last of the two tv had done a very sad end because after fixing the tcon i have put it in place and due to the proximity of that f***ing ferrite ring i have put one flat in the socket in the wrong mode and one cof chip on the screen cooked, so pay much attention, i love theese sets and my heart suffered seeing this beautyful thing dismantled for pieces and the earn fly away..

Well i have found the info in my phone where i'm writing, the part i have used is a FDS6982AS instead of the original FDS6930B. Bye.

[budm]

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

Since you did not use the T-CON that actually matched your original board, so your test result is not really valid, you also need to match the T-CON PCB assembly number as printed on the bar code sticker not the blank PCB P/N number printed on the board.

[Davi.p]

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

The tcon is the original one unless he doesn't mention, but seems the correct one..

[CMG97]

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

I think the old mainboard is broken. I can start it in service mode and I can turn it off with the button in this case, but if I start the TV in regular mode, then the TV simply shuts itself down after 30-60 secs. With the new mainboard though, I can start it in a normal way and turn it off properly. It is possible that I might be stuck in an initial setup menu with the new mainboard, and because of that I can't produce any sound through a HDMI cable. (Speakers are powered with 6.09 volts after starting)

I didn't change the T-CON board (so it matches with the original LE730E mainboard), because I thought that if the mainboard is broken than this new mainboard should work with this T-CON since they are the same DUNTK4593TP boards. But if I understand it correctly according to budm it isn't enough that they are the same type, but the sticker should also align with the mainboard. Just to be clear, are we talking about the 'YB' sticker now, or about the number below the QR code


Anyway, I did some measurements.
I have measured the FET301:


So I noticed that it only gets 0.5V and started to search for the panel source. Measured part of the cable power pins that goes to the T-CON board from the mainboard:



Then I ended up at this part of the board:



Here is the writing diagram:



So I suspect that the mainboard recognizes that something isn't right with the T-CON board, so it shuts it down and that's the reason it doesn't start the backlight either. So if that's the case, then:
a.) the T-CON is fine but doesn't match the mainboard, so it won't power up. (In this case I think is mission impossible to find a corresponding T-CON to this mainboard)
b.) if the TV should work with similar T-CONs with different stickers and the T-CON is broken, then replacing it should solve the problem

Do you guys have any idea what could cause the lack of T-CON power enabling signal?

[nomoresonys]

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

Maybe unplug the tcon from mainboard and see if the mainboard has the required 12 volts coming off those what is it 4 or 5 pins usually on the end of the connector or where it plugs into mainboard.

[nomoresonys]

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

Might find service manual there:

[CMG97]

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

Thank you for the manual, I have this service manual and linked this in my 2nd post (bottom) and using it. (Source of the pictures I edited)

I unplugged the tcon as you suggested!

So without the TCON plugged in the voltage on the 12V pins are reaching about 10-11V immediately after powering on and then slowly decreasing. (It's like a capacitor loosing charge slowly)
With the TCON plugged in, the peak is about 1.5 V and then slowly decreasing again. I think the reason I measured 0.5V is because I did't measure it immediately after powering up.

[nomoresonys]

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

Ok, seems like a mainboard issue to me after those results, thinking they should be around 12 volts and steady.

[Davi.p]

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

Yes the version sticker must match, if you want i have dumps of the 25x20 flash of the ZZ and ZY version which is the only thing that changes between boards, but is not useful because the memory must match the panel chacteristic, so no way changing the board, but for now try to measure voltage on VCC12V before the mosfet that enables PanelVCC, your check on the FET301 is not exact, the 0,5v are surely enough the source pins, but them are not near one to other, the pins 1>8 are: S1,G1,S2,G2,D2,D2,D1,D1, check with diode meter between D1-S1 and D2-S2, one way and opposite, it must not check 0v both ways, otherwise it's broken. You can also power the tcon with external smps 12v supply and if it goes in protection fet301 is bad. The difference in behaviour between boards is much probably 'cause the original one have the correct programming for the tcon/panel, so the new board does not recognize the panel so behave differently.

[CMG97]

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

Thank you for your suggestions!

I did the measurements.

The T-CON power supply part:



The FET301 voltages (After 5 mins of powering on the TV):



The FET301 voltage drops:


I think the 0.069 V and 0.046 V voltage drops are indicating that this component is probably faulty. The T-CON power part seems to be OK. It gets a consistent 12.1 V power and only the control signal from the FRC is missing. Based on my previous measurements, I think the FRC tries to power up the T-CON board (thus the instant voltage jump after powering up the TV) and fails. Does this make sense, or these TVs can't do that? Davi.p, do you remember if the LC-46LE630E had backlight or no? Were the symptoms similar as in this case?

Thank you for all your help again!

[Davi.p]

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

You don't have to mind if backlight is present or not, refer only to the original main board, it does not boot because it goes in sw error, as you can see from the m.b. panelvcc switch circuit the software shuts down this vcc, so no messing aroung, change that mosfet with confidence...
Just to be.sure jump for an instant s1-g1 to discharge the mosfet gate then re test s1-d1, if it is again zero volt then it is cooked.

[CMG97]

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

I remeasured s1-d1 after shorting the s1-g1. Also did it after turning it off, unplugging and waiting. Same results with the voltage drop. I have ordered the parts. Should get it by wednesday, will get back to you if I succeed and the TV starts.

Thank you for your help!

[budm]

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.