Sharp LC-40LE550U no backlight

[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

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

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

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!

[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?

[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

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

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.

[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?

[Markpixley]

Re: Sharp LC-40LE550U no backlight

76.2 vdc

[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

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

[Markpixley]

Re: Sharp LC-40LE550U no backlight

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

Nikos
PO425AD
WUE900302

[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

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.

Correct...now here's a question...

The Rich Tek chip (UD101)

Pins 13/12 each show 10 volts (led 1/2)
Pins 10/9 show no voltage (.004) which would be led 4/3

Vin is 12v
Fault is 12v

Is this chip ONLY being used for two led diagnostics? and pins 10/9 would never be used anyway?

[Markpixley]

Re: Sharp LC-40LE550U no backlight

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.

Forgive me for being dense (Thick as a brick per Jethro Tull)...

I start with 340 volts and end with 76 but no light...so where in hell is all that voltage going?...if it was open I would not see any voltage at the last pin...

If there is a short...?

[budm]

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

Looking at those reading for the Vf of each string, for example: the first string is 340 - 286 = 54V, so average Vf of each sting is about 52V which is not right since ten 6V LED should be 60V per string.
It looks like the MOSFET QD101 is not being turned on.
I need to look up the spec the IC UD101 to see how it function.

[Markpixley]

Re: Sharp LC-40LE550U no backlight

So far the info I have gathered on the niko is it is not schothy or esr, it can maintain up to 800 rds volts on 10v...seems like it goes up to 4 amps 512 pf Ciss typical...

[Markpixley]

Re: Sharp LC-40LE550U no backlight

Looking at those reading for the Vf of each string, for example: the first string is 340 - 286 = 54V, so average Vf of each sting is about 52V which is not right since ten 6V LED should be 60V per string.
It looks like the MOSFET QD101 is not being turned on.
I need to look up the spec the IC UD101 to see how it function.

Yes its actually a little more each string has eleven led's so the voltage required is 66volts...

[Markpixley]

Re: Sharp LC-40LE550U no backlight

I flipped the psu over and have it plugged in, powered up and the Mosfet QD101 reads 12.44v bottom leg at left, 14.17v bottom leg right (same as pin 13 on UD101) and 79.2v (same as Cn203 pin 5/bottom rail of led return)