UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt fix!

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

I'm prolly completely wrong with that guess, it's probably that your tester isn't putting out enough current to trigger the bad led so they light up, I don't really know what else would make it test at 280 instead of 192.

if the LED driver circuit on the PSU functions anything like my cheap LED tester then the open voltage of 280v would indicate open string... if the circuit were closed and current flowed, the voltage would drop based on what amperage the LED circuit wants to draw.

my LED tester will appear 320v when probes have no path to each other. when there is a path (through a single, or multiple LEDs) that voltage drops to whatever the forward voltage drop of the LED's is at whatever amps the thing is designed to provide...im not sure how it tells what the forward voltage drop should be so it doesnt burn out the LEDS...does this just happen automatically due to math of the constant current?

so this makes it look like my LED strips have open circuit according to the PSU
but according to my LED tester they have closed circuit. can the circuit open up that fast under "hot" condition (full power) that an LED wont even have time to flash? this is my gnawing question.

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Answer to post #50:
yes, i've already thought about a very cheap repair by adding some extra hidden leds or you can add simply a normal diode with similar Vdrop, who knows? I'm no more in tv repair hobby business so i have repaired few bad leds tv.. i have still one of them of the type "1 out of 10 times B.L. does not lit" to repair.. maybe it's time to fix it..

Answer to post #51:
Eazybone one must know how much is rated your tv PSB output, surely is higher than your tester's 100mA, so the fewer the leds you test, the higher the inrush current them takes, you have in some way activated a sleeping led, but it is still a damaged led and must be replaced..

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

IF you haven't a led bar you can simulate a led with 3 1n4007 diodes in series..

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

IF you haven't a led bar you can simulate a led with 3 1n4007 diodes in series..

oh nice so just 180 of these diodes in series and i can trick the power supply into thinking the LEDS are there!

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

I don't understand if I should laugh...

[EazyBone]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Thx davi, yes I fixed that led anyway lol I wasn't gonna mess around. Taking apart a 75 is definitely a challenge. Plus they taped down the screen on 3 sides. Is that really friggin necessary lol.

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

I don't understand if I should laugh...

yes sir. it was a joke. please laugh!

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Thx davi, yes I fixed that led anyway lol I wasn't gonna mess around. Taking apart a 75 is definitely a challenge. Plus they taped down the screen on 3 sides. Is that really friggin necessary lol.

75 is huge! ive never opened the panel on one that big. this one did have tape holding down the bottom edge of the panel. SUPER annoying.

[triplefour]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

i will have to put this TV on hold for now... gonna order the stronger LED tester. wish someone would give me a recommendation which one to get though!

[nomoresonys]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Looking at amazon and ebay, it seems that they are only going to 150 mA and 320v so any I guess one of those, they seem to be about 40-50 bucks or so.

[Davi.p]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

You could make a simple cheap tester about 30$ with This
for input diodes you could use 4 1n4007 or an integrated one.. you could power until about 870mA Backlight.. if could be a problem you could limit inrush current with an NTC in series..

[nomoresonys]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

That one is 32 bucks: https://www.ebay.com/itm/20244289449...pid=8059995264

[nomoresonys]

Re: UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt f

Your in HI, so your going to be hit with shipping charges from almost everywhere, china is the only place that has secured themselves those shipping advantages they were allowed all those years ago when they were deemed a "developing economy" Well poor little china, I guess they're still a "developing economy": https://hbr.org/2020/02/how-much-mon...orld-owe-china