sharp 50-lb371u leds problems

[robert phelps]

hello, i have a sharp lc-50lb371u set thats has bad leds backlights. the first time i took the set apart i replaced 2 leds that were bad. the set worked good until i put it back togerther and then it only worked for about 10 minutes. i replaced the leds with some from another strip i had. took the set back apart and found 3 leds out this time. replaced with same ones i had. set worked for about 15 hours being on and then the bottom led strips were a little dimmer then the top ones. this set has 6 strips of leds, the top 4 are on led1 off the psu, the bottom 2 are off led2 off the psu. after turning the set off then back on no backlights again. i know these sets have a led problem, but what i need to know is the psu when you plug it in has no voltage on led1 or led2, when you power on the set the voltage goes to 64.8 to 95.6 then back to 64.8. i think that should be correct for this set. the problem is when you turn the set off the 64.8 voltage does not turn off. the psu still has a little hum of it working. seems like it should turn off completly. the only way to kill the 64.8 led volts once the set is turned on is to unplug it or unplug the logic board. someone plesae help, having a hard time finding led strips for this set and dont reaaly know if psu may be causeing this or logic board not shutting down psu like it should

[dick_barton]

Re: sharp 50-lb371u leds problems

Were the replacements from another strip which matched the existing led strip for the set or just a set of similar leds?

[robert phelps]

Re: sharp 50-lb371u leds problems

just a set of similar leds

[robert phelps]

Re: sharp 50-lb371u leds problems

Pics

[dick_barton]

Re: sharp 50-lb371u leds problems

I suspect that's your problem. Many leds look similar but can have different maximum current ratings. There are also 3V and 6V versions. You need to replace them with leds from an identical strip intended for that panel. It's highly probable that the ones you replaced them with were lower current rating and have stressed the existing ones causing further damage.

[robert phelps]

Re: sharp 50-lb371u leds problems

but what about the psu not killing the 64.8 volts going to the leds when the set is powered off. should it go to 0 then when turned off

[robert phelps]

Re: sharp 50-lb371u leds problems

im not thinking its just the leds here. the set is only 2 years old

[dick_barton]

Re: sharp 50-lb371u leds problems

If you were to read the many threads regarding led faults you will see that what you are describing fits the problem you have.
What is the LCD panel name and number as given on the metal back?

How many leds per strip and how many strips are there?

[budm]

Re: sharp 50-lb371u leds problems

What is the spec of the replacement LED?
Vf and If rating are very important.

[robert phelps]

Re: sharp 50-lb371u leds problems

But what about the psu not shutting down the 64.8 volts when you power the set off

[robert phelps]

Re: sharp 50-lb371u leds problems

The leds I replaced worked for awhile

[budm]

Re: sharp 50-lb371u leds problems

What you need to find out if the PS-ON (ON = >2 VDC (OFF = <1 Vdc) goes low when the TV is off or not.
Same for the BL-ON (same as O/F).

[robert phelps]

Re: sharp 50-lb371u leds problems

The panel number is tpt500j1-hvn07.u. there are 6 strips 11 leds per strip. 4 strips are off led 1, 2 strips are off led 2. Both have 64.8 volts all the time

[robert phelps]

Re: sharp 50-lb371u leds problems

Thanks buMD I'll try that in the morning and see what I can figure out

[dick_barton]

Re: sharp 50-lb371u leds problems

I'm surprised that they are not balanced and that Led1 & Led2 support 3 strips each.

[dick_barton]

Re: sharp 50-lb371u leds problems

Can you post a sharp photo of the bottom of the power supply to identify the led driver IC

[robert phelps]

Re: sharp 50-lb371u leds problems

Here are pics of psu

[attainteddragon]

Re: sharp 50-lb371u leds problems

db needs to see picks of the under side of the ps to see the backlight circuitry.
clear straight on pics, thanks.

[robert phelps]

Re: sharp 50-lb371u leds problems

the psu connector going to the logic board has 16 pins, 6 of them are 12v which is alway there on/ 2 are listed as 12v_a dont know what the underline means for these 2 pins. the ps_on , dim , and o/f are o volts when you plug the set in. when you power the set up ps_on goes to 3.34, the dim goes to 3.09 and the o/f goes to 3.32. when you power the set off the ps_on stays at 3.34v and the dim stays at 3.09 volts. the o/f does go to 0volts. meanwhile the led1 and led2 also stay at 64.8 volts any ideas of what could be going on. i have read these set are bad on leds but maybe its not the leds fault , maybe logic is keeping psu on all the time killing them

[budm]

Re: sharp 50-lb371u leds problems

http://www.shopjimmy.com/sharp-pltve...c-50lb370u.htm

Sharp PLTVEY701XAL5 Power Supply / LED Board for LC-50LB370U

Your board is XAL4, but this one looks to be the same as yours.
Pictures provided by shopjimmy.