sharp 50-lb371u no backlights

[robert phelps]

this is a new one on me, looks like the backlights are leds. i have sound and the startup menu but no backlights. power led flashes 7 times and set comes on. my next post will be of pics, easier for me to serch and type with computer insted of my phone which i take pics of

[robert phelps]

Re: sharp 50-lb371u no backlights

well i tryied posting pics from my phone don t know where they went hit upload and then nothing. anyway i have 64.8 volts going to i guess the leds behind the panel. i seem to be missing a 15.5 volt on the psu cable that goes to ligic board other voltages are right on that connector the only one maked what they should be. can anyone help

[robert phelps]

Re: sharp 50-lb371u no backlights

also led on front flashes 7 times and comes on

[petehall347]

Re: sharp 50-lb371u no backlights

can you see a picture when shining a light on the screen ?

[robert phelps]

Re: sharp 50-lb371u no backlights

yes

[dick_barton]

Re: sharp 50-lb371u no backlights

Can you post clear and sharp pictures of your power supply and what voltages you have at the connectors including the pin names all which would prove helpful.

[robert phelps]

Re: sharp 50-lb371u no backlights

Here are some pics

[robert phelps]

Re: sharp 50-lb371u no backlights

On the psu I have 64.8 volts on the red lines that goes into back of panel. The yellow should be 15.5 volts but don't have it. Other volts are there

[Andrew F. Ali]

Re: sharp 50-lb371u no backlights

1. Measure the voltages on the 2 LED+ pins. If the voltage goes high and then settle off to 50% -75% of high voltage measured then we can think the Power is OK.

2. Measure LED- pins, they should measure 4V-10V. If they are 0V, we can say the LEDs are 'open' and need to be replaced.

If the LED-pins are high approx. 30V, this would indicate an open Driver on the PSU. Take a 100ohm resistor and place one end on chassis ground and the other end on the high LED- pin. When the power is applied if the LEDs turn on, then you have confirmed a bad Driver on the PSU.

[dick_barton]

Re: sharp 50-lb371u no backlights

If the 15.5V is missing I would be looking to see why. Can you check underneath of the power supply pcb to see if those pins are in use. A photo of the underneath would be useful.


Edit
Looking at you power supply pcb it looks like the 15.5V is not supplied on this board. There are several components not included on the board (alongside the connector) which I feel would be connected to provide the missing 15.5V line.

So it looks like Andrew F. Ali comments to concentrate on the leds is the correct step to take.

[robert phelps]

Re: sharp 50-lb371u no backlights

ok will try check back in a while thanks

[robert phelps]

Re: sharp 50-lb371u no backlights

ok here what i got my red leads when power on are 64.8 volts then go to 95.8 volts then back to 64.8 volts both red leads led1 and led2 i guesss. the black leads are .04 volts not 4to 10 so are the leds backlights bad and is there a way i check them before pulling the whole set apart.

[robert phelps]

Re: sharp 50-lb371u no backlights

when i power this set off its kinda hard to tell but seems like led flashes 2 long pause 2 short flashes and then 1. any ideas

[jjanssen7]

Re: sharp 50-lb371u no backlights

Bad LEDS are common on that model...

[dick_barton]

Re: sharp 50-lb371u no backlights

What voltages do you have on pin 2 of CN9100 when you switch the set out of standby. Also I can't quite make out what it says alongside it ?

[robert phelps]

Re: sharp 50-lb371u no backlights

pin 2 is labeled o/f and its 3.3 volts when powered on

[robert phelps]

Re: sharp 50-lb371u no backlights

if one led is bad because they are wired in series how come you can check them with an led/lcd teste? seems like if the psu is sending them volts they should light just like with a tester

[dskall]

Re: sharp 50-lb371u no backlights

They will flash on then the board protection will shut them down. Tester doesn't have that protection just maintains a certain current

[budm]

Re: sharp 50-lb371u no backlights

If one or more of the LEDs shorted out, the whole string will stll light up with the tester, but the circuit that drive the LEDs will detect the over current condition and goes into shutdown. You have to look at what the Vf Voltage is display on the tester and compare it to known good strip to see if it shows the same Vf Voltage. You have to know how to read the result as shown on the tester.

[jtz54]

Re: sharp 50-lb371u no backlights

I'm testing a no backlight condition on my Sharp 50-LB371U unit. From what I've read so far on this thread the PS board will sense an "out of normal" condition and shut off. I had replaced the PS board and the unit was working briefly but now there is no backlight again. There is no voltage to the LED strips. There are 6 sets of L & R LED strips, the power connector is connected to the R strip which connects to the L strip. If I apply 12V to the connector on the L strips all LEDs light up. The R strips don't do the same as I haven't gotten them to light up unless I apply voltage to each LED but I found at least one bad LED on each of the R strips. Is this unusual? I noticed there are two LED driver on the PS board but since the R & L sides seem to be in series it doesn't make sense the R ones going bad?