Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

[bbccbb]

I have a problem with this LED TV power supply. Sometimes it powers down LED backlight. There is no way to predict when it is going to happen. Sometimes it works 5 hours. Sometimes backlight switches off after 10 minutes. Switching it off and on again solves the problem for some time (sometimes for few minutes, sometimes for few seconds and sometimes for few hours).
I cannot reproduce the problem when needed… I have to wait for it.
I've made some photos of the layout, Vestel power board and main board.
I've also measured voltages on same points when the backlight is on and when it's off.
Measurements were made only on the non-SMD side as I could easily access it.

The radings of voltages betwen chasis and some points (https://docs.google.com/spreadsheets...it?usp=sharing):
point V when working V when not working
connector CN501 LED red wire 168 119
connector CN501 LED black wire 25 21,7
diode D504 C 164 118,8
diode D504 A +++ 119,1
J85 0 0
C2582 - -0,02 0
C2582 + 168 118,8
J25 11,99 12,3
J45 11,99 12,3
J34 0 0
resistor R574 right 120 119,2
resistor R574 left 20 18,8
J6 10,27 10
J7 0,6 0,1
Q216 E 10,5 10,5
Q216 B 10,8 10,8
Q216 C 10,1 10,3

J94 -0,02 0,01
J95 -0,02 -0,01
J96 -0,02 -0,02

F507 +++ 55,5
F506 +++ 55,2

D360 C 59 59,1
D360 A +++ 119,1
C316 + 119 119,1
C316 - -0,02 -0,01
J55 0,05 0,06
J51 -0,02 -0,02
J12 -0,02 -0,02
C392 + 120 119,1
C392 - -0,02 -0,01
C317 + 120 119,1
C317 - -0,02 -0,01
D226 C 12,41 12,41
D226 A -0,08 -0,05
D225 C 12,41 12,41
D225 A -0,08 -0,05
D209 C 12,41 12,41
D209 A -0,08 -0,05
J30 10,27 10,21
J42 -0,1 -0,1
Q301 G 1,15 -0,2
Q301 D +++ +++
Q301 S -0,09 -0,1
R320 top -0,09 0,02
R320 bottom -0,09 -0,2
C105 - -0,12 -0,1
C105 + 215 218
C534 - -0,12 -0,12
C534 + 215 218
Q211 G 0,4 0,4
Q211 D +++ +++
Q211 S -0,12 -0,12
J20 215 218
J81 215 218
R235 top -0,08 0,03
R235 bottom -0,08 -0,12
D206 C 312 310
D206 A +++ +++
D506 C 214 217
D506 A +++ +++
D100 C 214 217
D100 A 121 158
Q100 G 1,52 0,23
Q100 D +++ +++
Q100 S -0,09 -0,1
D115 C 122 161
D115 A 61 74,3
D114 C 61 74,3
D114 A -0,08 -0,08
D113 C 122 160
D113 A 61 73,4
D112 C 61 73,4
D112 A -0,08 -0,08

C212 + 12,4 12,4
C212 - -0,02 -0,01
C211 + 12,4 12,41
C211 - -0,02 -0,02
C210 + 12,4 12,41
C210 - -0,02 -0,01
C209 + 12,4 12,4
C209 - -0,02 -0,02

J71 -0,02 -0,02
J66 -0,02 -0,01

J49 0,04 0,09
J17 0,04 0,04
J78 0,04 0,02
J50 119 119,2
J52 119 119,2



Any ideas?

[ReeceyBurger123]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

Connectors that link led strings are breaking down, open panel and bridge over them with solid wire.

[CapLeaker]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

To add to Reecey's comment: Turn down the backlights to next to nothing and see if the backlights stay on longer. If it does, then you have a problem with the backlight LED's.

[koka0011]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

it could be a faulty component in inverter.use hot air gun to heat up the inverter area.and measure the voltages ERR pin.try to measure ERR pin voltage and heat up the inverter area and check the voltage when it stops.you can find the bad component using heat up method

[dick_barton]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

The voltage across C105 should be 400V otherwise the FAN7529 is not operating.
Check diodes D101, D102, D506, Q100

What DC voltage do you have (carefully) between pins 8 & 6 of FAN7529. Check C127

Edit
What does Q100 D +++ +++ mean?

[ReeceyBurger123]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

I dont think he measured across the caps right DB thats why he has a low reading. These sets wont run if the fan Ic isnt working.

[dick_barton]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

Thanks. Didn't think of that. Just considered that the readings were taken when the backlights were off.

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

The voltage across C105 should be 400V otherwise the FAN7529 is not operating.
Check diodes D101, D102, D506, Q100

What DC voltage do you have (carefully) between pins 8 & 6 of FAN7529. Check C127

Edit
What does Q100 D +++ +++ mean?

+++ means that my voltmeter said "higher than 600".

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

Connectors that link led strings are breaking down, open panel and bridge over them with solid wire.

Ok... I'll do that. Thank you.

[dick_barton]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

When you lose the backlights are you also losing sound etc or just backlights.

When the backlights go off can you measure using your meter set to DC, the voltage between the two legs of C105 (meter probe either side of C105) which should be about 380 -390V

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

To add to Reecey's comment: Turn down the backlights to next to nothing and see if the backlights stay on longer. If it does, then you have a problem with the backlight LED's.

As I said before... there is no way to tell when it will turn off backlights. Sometimes it takes hours.

On one occasion it switched of backlights after 10 minutes. I've turnd the TV of and on again and it worked for 5 hours more. That's why I do not see hot to trigger this myself.

When you wrote "Turn down the backlights..." you ment using menues on the TV?

So, you say... if the same thing happens after soldering connections to the LED strips, then I have to wait for LEDs to stop working?

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

When you lose the backlights are you also losing sound etc or just backlights.

Only backlights. Sound working. Picture on.

When the backlights go off can you measure using your meter set to DC, the voltage between the two legs of C105 (meter probe either side of C105) which should be about 380 -390V

Ok... I'll do that. But I'll have to wait for few hours.

[dick_barton]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

You can ignore my previous request. If the sound is still working then as ReeceyBurger123 has already said the power supply is working otherwise you would not have sound.

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

You can ignore my previous request. If the sound is still working then as ReeceyBurger123 has already said the power supply is working otherwise you would not have sound.

So... then I have to make a better connection (directly soldering to the connector) to LED strips and then wait for some LED to fail. Right?

[CapLeaker]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

As I said before... there is no way to tell when it will turn off backlights. Sometimes it takes hours.

On one occasion it switched of backlights after 10 minutes. I've turnd the TV of and on again and it worked for 5 hours more. That's why I do not see hot to trigger this myself.

When you wrote "Turn down the backlights..." you ment using menues on the TV?

So, you say... if the same thing happens after soldering connections to the LED strips, then I have to wait for LEDs to stop working?

yeah... turn down the backlights using the Menu on the TV.

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

yeah... turn down the backlights using the Menu on the TV.

This would work if at some point TV would hold the backlight on for short time and I could test if it would work longer on lower energy consumption (or less heat on sam poart). But I do not get that. Once I turned of after 10 minutes. I restarted TV and it worked for 5 hours... I went to sleep and turned it of that night.

It would be better it it would stay dark all the time! I cannot deduce the problem from all this. That's why I asked for any pointers.

I'll make a fix connection between power leads and LED strips tomorrow. I think it will take me few hours. I'll have to be careful removing that LCD... if I brake it...

[vinceroger69]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

this video shows the type of repair you may have to do some strips i think are joined in the middle to so you may have to bridge them to, intermitant faults like this are always hard to find but do take care removing/replacing the lcd and do keep the diffuser sheets in the rite order and also try to keep away any dust/finger print free as best you can as these show up when the set is working.
https://www.youtube.com/watch?v=AeAGI0yNgEM

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

this video shows the type of repair you may have to do some strips i think are joined in the middle to so you may have to bridge them to, intermitant faults like this are always hard to find but do take care removing/replacing the lcd and do keep the diffuser sheets in the rite order and also try to keep away any dust/finger print free as best you can as these show up when the set is working.
https://www.youtube.com/watch?v=AeAGI0yNgEM

The guy on the video just removed the whole back metal cover with LEDs strips on it and plastic reflectors. That means that I could put my TV with LCD facing down on the table and leave a diffuser sheets on it.

Then I can solder all the bridges and reconnect all the connectors and that will be it.

Then I will have to test it to see if that was the cause off my backlight turning off.

[vinceroger69]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

all tvs are diffrent too disassemble etc so its whatever is the easiest on that make of tv re assembley is hard ive cracked a screen when clipping the black plastic surround back on so be really carefull and take it slow thats all i can suggest.

[bbccbb]

Re: Sharp LCD LED TV LC-39LD145V [C] - Vestel 17IPS20S, problem with backlight

Ok... I soldered all the joints. I'll post the photos of what it looked like. Now I'll wait to see if this solved my problem.