Sharp LC-40LE550U no backlight

[krygods]

This TV powers on and off and I can see the floating screen saver very faintly with a flashlight.

I've measure voltages and here is what I've found

CN201

1 - 3.25VDC
2 - NC
3 - 112mVDC
4 - 3.19VDC
5 - GND
6 - GND
7 - GND
8 - GND
9 - 12.45VDC
10 - 12.45VDC
11 - 12.45VDC
12 - 12.45VDC
13 - 375mVDC and rising???
14 - 3.18VDC
15 - 0.67VDC
16 - NC


CN202

1 - 329VDC
2 - GND
3 - 275VDC
4 - GND
5 - 221VDC


CN203

1 - GND
2 - 168VDC
3 - GND
4 - 116VDC
5 - GND

[retiredcaps]

Re: Sharp LC-40LE550U no backlight

CN201
3 - 112mVDC
14 - 3.18VDC

It would make things easier for us if you put the description of each pin next to the readings.

CN201

pin 3 - ACD
pin 14 - BL_ON

On most sets, BL_ON (backlight on) going high (> 3) means turn on. On some sets, it might be the opposite.

ACD might be AC Detect. On some sets, ACD high might be needed to turn on. Or it could be the opposite.

When the TV is in standby mode, what is the voltage of pins 3 and 14? When turned on what is the voltage of 3 and 14? When the set is turned off, what is the voltage of 3 and 14?

Wow, 329V DC into the LEDs. Nearly a 55 to 52 volt drop between each strip of LEDs. At least it has decent 47uF 450V cap there.

[retiredcaps]

Re: Sharp LC-40LE550U no backlight

13 - 375mVDC and rising???

pin 13 is NC. The 357mV reading is just your multimeter on high impedance with some ghost readings. NC is probably not connected to ground otherwise you would get 0V.

[retiredcaps]

Re: Sharp LC-40LE550U no backlight

This TV powers on and off and I can see the floating screen saver very faintly with a flashlight.

If the TV is in a very dark room, do the LED backlights flash even for a brief time?

[retiredcaps]

Re: Sharp LC-40LE550U no backlight

Hmm, from

https://www.sharpusa.com/ForHome/Hom...C40LE550U.aspx

4 million: 1 dynamic contrast ratio

Without even seeing the TV, I think I will call

[retiredcaps]

Re: Sharp LC-40LE550U no backlight

BTW, what is the marking in IC UD101, just right of 47uF 450V cap?

[krygods]

Re: Sharp LC-40LE550U no backlight

P/N for UD101 is RT8300

[krygods]

Re: Sharp LC-40LE550U no backlight

disassembled the panel to test the leds, found bad solder joints on one the of the connectors that join the two separate strips into one long strip. turned it on and the leds blinded me.

[CapLeaker]

Re: Sharp LC-40LE550U no backlight

perfect!

[budm]

Re: Sharp LC-40LE550U no backlight

So how many LEDs are in one strip? 4 LED strips?

[krygods]

Re: Sharp LC-40LE550U no backlight

I believe it was 10 LEDs per strip 5 strips

[krygods]

Re: Sharp LC-40LE550U no backlight

crazy thing is that four out of 5 led strips are mounted to the panel casing which is plastic, only the second strip from the top is mounted on a strip of metal. I was under the assumption that the LED strips needed to be mounted to metal which acts as a heatsink?

[budm]

Re: Sharp LC-40LE550U no backlight

They should have good thermal management, I would set the BACKLIGHTS LEVEL (not the brightness/contrast) to as low as you can so the LEDs will run cooler and extend the life of the LEDs.

[krygods]

Re: Sharp LC-40LE550U no backlight

ok cool, i'll go ahead and set it to a comfortable low level before it goes to a new home.

[retiredcaps]

Re: Sharp LC-40LE550U no backlight

P/N for UD101 is RT8300

The datasheet for the above has a FLT pin which detects open/short LED. Monitoring this pin for it going low points you to the LEDs as being suspect.

[Markpixley]

Re: Sharp LC-40LE550U no backlight

So I have the same problem, found two of the led connectors that needed resoldering...still no backlight...my voltages on CN202 CN203 are all pretty solid (with the exception of voltage dropping to 80 volts at the bottom of CN 203) (which is quite a swing if you ask me from 329v to 80v)...at any rate...

Checking UD101...pin 6 is the fault...I get 12 volts on Vin and 12 volts on Fault which seems to point to the leds again...also now that I've re soldered the leds I do get 10v on both pin 13/12 (led 1/2) but zero volts on pins 10/9 (led 4/3)...any idea what I should see there or do I go back and take the panel apart yet again and search through the led connectors...really cheaply designed solder joints for the connectors...not much effort to knock them loose...

[budm]

Re: Sharp LC-40LE550U no backlight

You are seeing the Voltage to the LED swings all the way up to 329V because there is no load due to open circuit (either by bad connector or the LED has open circuit, when the circuit see that high Voltage that is above the normal operating level then the over Voltage shutdown kicks in then it drops down to 80V which is the Voltage that is fed into the Boost converter circuit to drive the LED strings.

[Markpixley]

Re: Sharp LC-40LE550U no backlight

You are seeing the Voltage to the LED swings all the way up to 329V because there is no load due to open circuit (either by bad connector or the LED has open circuit, when the circuit see that high Voltage that is above the normal operating level then the over Voltage shutdown kicks in then it drops down to 80V which is the Voltage that is fed into the Boost converter circuit to drive the LED strings.

Ahhh thank you, back into the panel to check it will let you know what I find...great forum by the way!

[Markpixley]

Re: Sharp LC-40LE550U no backlight

Ok I have physically checked each and every LED with a diode test they all gave me OL one direction and .889 the other, I also checked each and every connection with a continuity test and everything came back ok...

Voltage with reference to ground (negative clip on metal ground Meter set to DC) goes from 340, 286, 233, 180, 128...there are 5 strips with 11 led's each...

But no back light...is it possible that this unit needs some kind of factory reset since it did have a faulty connection on one LED strip?

Would the UD101 go into LED fault and need to be reset somehow? Thanks in advance...

[Markpixley]

Re: Sharp LC-40LE550U no backlight

I also have another question since i have never seen these before, but what is the clear diode looking fuse item labelled SG105 in the bottom right hand corner of image #2?

Is it some sort of slow blow fuse and if so is there a way to test it? It seems to connect ground planes on the back of the psu...but I am unfamiliar with it.