Sharp LC-40LE550U no backlight

[budm]

Re: Sharp LC-40LE550U no backlight

76.2 vdc

OK, so there is no open connection on the LED strings, and you can get all the LEDs in each strip to light up OK.

[Markpixley]

Re: Sharp LC-40LE550U no backlight

BTW, what is the P/N of the LED backlights controller IC UD101?

Nikos
PO425AD
WUE900302

[Markpixley]

Re: Sharp LC-40LE550U no backlight

the voltage to Cn202/cn203=

1. (+) 340
2. (-) 286
3. (+) 286
4. (-) 233
5. (-) 233

1. (-) 180
2. (+) 180
3. (-) 128
4 (+) 128
5. (-) 77.8

[budm]

Re: Sharp LC-40LE550U no backlight

BTW, what is the P/N of the LED backlights controller IC UD101?

[Markpixley]

Re: Sharp LC-40LE550U no backlight

76.2 vdc

[budm]

Re: Sharp LC-40LE550U no backlight

What DCV do you have on pin 5 of CN203, that the LED string return line to the PWM Controlled power MOSFET QD101?

[budm]

Re: Sharp LC-40LE550U no backlight

So you can light up each LED strip individually using external power supply.
You have 5 LED strips, each strip has 10 LEDs, each LED is rated at 6V, so total Vf is 50 LEDs x 6V = 300V, and you have 329V feeding the strings per post #1 but you never see the LEDs light up at all.
It means you have open connection between the 5 set of the LED strings some where, or the LED return through the Power MOSFET is not active.

[Markpixley]

Re: Sharp LC-40LE550U no backlight

Thanks budm, you have been very helpful...

So here's where I am at...I used a 12 volt psu and tested all the LED's (based on your suggestion that they are double and 6 volts)...every pair I tested lite up brightly and all my continuity test on the strips seem to be solid...

Unit power light turns green...I can get it to turn red but it takes a bit...and it usually just flips back to green...

No back light...at all voltages still as earlier...

Without being to much of a bother what might be my next course of testing?

[budm]

Re: Sharp LC-40LE550U no backlight

Surge Arrestor, as you can see, some of them are connected in parallel with the inductor windings so you see very low DCR.

[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.

All the other "SG" parts show a continuity test beep, EXCEPT this one in the corner...is this some kind of time delay fuse or capacitor part?

This one is not giving me any response, Ohm or continuity at all...

Does "SG" mean surge guard?

[Markpixley]

Re: Sharp LC-40LE550U no backlight

If you look at the LED connectors in deatails, you can see that the LED strips are connected in series to form ONE long LED string, if ypu look at the bottom side of the power supply board where the LED connector CN202 PIN 1 (+) is connected to the LED power supply filter cap CL115 positive leg, the pin 1 of CN202 goes to the first LED string ANODE, the negative return goes to CN202 PIN 2 (-) this (-) is then connected to the Anode (CN202 pin 3) of next LED string, and on and on to the fifth string.
So as you can see, the LED connectors are terminated as series connections for the 5 LED strings, if one goes open circuit then the whole backlights will not be on.
Pictures provided by shopjimmy.
Sharp 9JY0940CTJ05000 (FTPL-009) Power Supply Unit.
http://www.shopjimmy.com/sharp-9jy09...pply-unit.htm#

Ahhh very helpful again it takes some of the voodoo out of it...making moire sense Thanks!

[budm]

Re: Sharp LC-40LE550U no backlight

If you look at the LED connectors in deatails, you can see that the LED strips are connected in series to form ONE long LED string, if ypu look at the bottom side of the power supply board where the LED connector CN202 PIN 1 (+) is connected to the LED power supply filter cap CL115 positive leg, the pin 1 of CN202 goes to the first LED string ANODE, the negative return goes to CN202 PIN 2 (-) this (-) is then connected to the Anode (CN202 pin 3) of next LED string, and on and on to the fifth string.
So as you can see, the LED connectors are terminated as series connections for the 5 LED strings, if one goes open circuit then the whole backlights will not be on.
Pictures provided by shopjimmy.
Sharp 9JY0940CTJ05000 (FTPL-009) Power Supply Unit.
http://www.shopjimmy.com/sharp-9jy09...pply-unit.htm#

[Markpixley]

Re: Sharp LC-40LE550U no backlight

The 0.89V is the Vf of the protection diode not the White LED Vf, you need to reverse the probes to read the Vf of the LED which it should be around 2.8- 3V.
It can also be that your meter does not put out enough Voltage in Diode mode to turn on the White LED.
It can also be dual LED in one body so the Vf will be around 6V.

Thanks for the response, so down that road would it be about as smart to make a simple power supply and test each LED since I have already scratched the surface to diode test them? Just do the 3 volt test and see if they light?

It seems odd to me that there are 5 distinct strips and 10 power leads, if a single led was out wouldn't that simply stop that strip from working instead of all five strips?

I am not techy enough but trying...(I actually build vintage tube recording gear so this lower power stuff is all new to me)

[budm]

Re: Sharp LC-40LE550U no backlight

The 0.89V is the Vf of the protection diode not the White LED Vf, you need to reverse the probes to read the Vf of the LED which it should be around 2.8- 3V.
It can also be that your meter does not put out enough Voltage in Diode mode to turn on the White LED.
It can also be dual LED in one body so the Vf will be around 6V.

[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.

[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

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!

[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

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...

[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.