SHARP LC-60E635E no backlight and picture

[Edward Wong Hau]

Hello, I recently got a 60" LED Sharp TV. The problem is that every time I power it on it will just switch on the power LED and try to powerup 3 times (LED stays on for long switches off and then on again) after that it will flash the LED 3 times pause and flash 3 times again until I pull the plug. I opened the thing and took out the PSU, witch on this TV is a LED backlight circuit / PSU combo. Btw. I have also looked at the panel with a powerful touch to see if anything is displayed but its not. I have checked all caps, mosfets (main supply), optocuplers and diodes for defects all are working perfectly fine. I measured the voltages to the LED mosfets (63v) and the 5v to the mainboard. The only problem i could find was that the mosfets that should switch the power to the backlight don't let the voltage through. No voltage on gate and output 63 on source. The 4 parallel fets are controlled by 4 BD9285F ics underneath (https://cdn.badcaps-static.com/pdfs/...9a461d70f9.pdf). I have checked vcc and uvlo (4.7v) these things are new to me so I don't relay understand why they don't let the voltage through. It could be a protection feature but the mosfts look fine (haven't desoldered them yet but they all read the same) and they don't even try to power the mosfets tried to capture the voltage but nope. I don't get it , does anyone have an idea how these ic's opperate and what the problem could be?

[dick_barton]

Re: SHARP LC-60E635E no backlight and picture

VCC for the BDB9285F is given in the data sheet as a minimum of 9V and a maximum of 18V to operate correctly.

[Edward Wong Hau]

Re: SHARP LC-60E635E no backlight and picture

Thanks for the quick response , I think I will measure the vcc next. But I don't think it will be a problem as the chips are connected to the 63v rail through a series of resisters, that lower the voltage to the ic's needed voltage. Is 63v a usual voltage for LED's? It might be to low which means the controllers wouldn't get enough voltage too but I already checked most of the components in the dam supply and it seems pretty steady.

[dick_barton]

Re: SHARP LC-60E635E no backlight and picture

The working led voltage is often written on the power supply circuit board. I would be surprised if the VCC supply for the BD9285F was derived from the 63V supply. I suspect that's the voltage required to be boosted by the BD9285F to drive the leds.

Can you post pictures of your boards. Do you have a schematic for your set?

If you do a search for your model it gives the error codes.
http://www.toms-service-manuals.com/...h=Submit+Query

[Edward Wong Hau]

Re: SHARP LC-60E635E no backlight and picture

I have tested the input voltage and it's at 13.17v seems to be fine but I just checked the resistance of the led connector for all 4 pairs in both ways and I get absolutely 0 resistance for what i am measuring the backlight circuit is completely open and the driver chips have open circuit protection. Is this maybe the problem? Also the TV does exactly the same thing if i unplug the LEDs but it doesn't care much about the absent Tcon ether if i unplug it . I don't want to take the panel apart unless I relay have to, any suggestions? Is this normal?

[dick_barton]

Re: SHARP LC-60E635E no backlight and picture

The 13.7V for the driver IC is within the specification.

0 resistance is a short circuit. I assume you mean it appears open circuit which is what you would expect for a string of leds.

What does the voltage jump to on the back light connector with the back lights disconnected when you first switch on.

Does the blinking led on the front of the set follow any of the error codes given in the manual on Tom's website???

How about some sharp clear photo's of your circuit boards and how they all connect.

[Edward Wong Hau]

Re: SHARP LC-60E635E no backlight and picture

Yes I meant open circuit thanks for saving me the disassembly of the panel, but it doesn't make a difference in voltage if I disconnect the LEDs its always something like 0.5-0.1 falling because of capacitance in the circuit. I found out something new in the manual by pressing the menu button the flashing LED gets more specific to whats the problem. Its 3 times long then one short flash. This apparently means: "Initial communication from the main CPU is not received.
(Request for the monitor model No. is not received.)
 Communication line failure or main CPU start-up failure." But a guy on youtube had the same error and after replacing the PSU evorything worked again. I have checked the voltages to the mainboard 13.5 something, well in spec the 5v rail is perfect too but pin one and two are that are marked PNL12v have no voltage on them. The thing is as far as I can see this is supposed to be like that this 12v regulator () has a 100k resistor between the on/off and ground. I tested the thing on a breadboard with a 100k resistor and same result but if i remove the resistor it outputs 12v. I'll post some pictures.

[dick_barton]

Re: SHARP LC-60E635E no backlight and picture

According to the data sheet if pin4 of the 12V regulator is taken to ground or to 0V then it switches off the output supply. If the input to pin 4 is high (greater than 2V) or left open circuit then it switches on the output voltage.

[Edward Wong Hau]

Re: SHARP LC-60E635E no backlight and picture

I traced the switch to the PNL-POW pin of the PSU and its supposed to power on the regulator. I found a similar problem in this thread: (https://www.badcaps.net/forum/showthread.php?t=49341).

[dick_barton]

Re: SHARP LC-60E635E no backlight and picture

The 12V regulator is working because you said when you tested it on the breadboard there was no output when you tied pin 4 to ground using 100K resistor but when you remove the resistor you had output voltage.

I further suspect that the PNL-POW pin is "Power to the LCD Panel" which may not be activated by the main board if it detects a fault condition with the back lights.

[Edward Wong Hau]

Re: SHARP LC-60E635E no backlight and picture

I have measured the voltage on PS_ON (2.85v) and PNL_POW (1.random). The PNL_POW is a input from the Mainboard and seems to vary a lot, and the PS_ON appears to be to low i don't know for sure but in the other thread the PSU used the 5v to power on, the opto cuplers seem to run pritty low too 1-0.8v and i think they turn on with the PS_ON voltage.

[Edward Wong Hau]

Re: SHARP LC-60E635E no backlight and picture

I think the problem is with the Motherboard so I will try to get a cheap one with broken HDMI ports and try that.

[dick_barton]

Re: SHARP LC-60E635E no backlight and picture

Can you check when you switch on if there is a lamp detection error which can be reset. Section 5, page 43 of the service manual from Tom's web page guides you through the test.