Sony Bravia KDL-42EX440 - problem - turns off after switching on

[zarko]

My parents gave me a Sony KDL-42ex440 TV to repair it for them.

When I plug the TV in mains, the power LED (green) turns on immediately. After few seconds the back-light flashes for a moment and immediately back-light goes off.
After about 5 seconds TV shuts down (no LED is on). The slight pop sound can be heard from speakers while the TV switches off.
If I want to turn the TV on I must unplug it from mains and plug it again.

I have tried and I can confirm that panel is showing picture after the back-light flash (while the back-light is not on) - I pointed strong light from the front of the screen in order to see the image on screen.
I can see "Sony logo" shown in the middle of the panel and after that "input HDMI 2" in top-left position of the panel.
It seems like T-CON board is OK.
I tried unplugging LDVS cable from the main board, TV shuts off again.

TV can be switched into stand-by mode using IR remote and also using controls on TV (this can be done before the TV goes OFF).
TV goes to stand-by and it can stay that way until I turn it on using IR remote or controls on TV.
After that the complete sequence I explained above repeats until the TV shuts down.

I updated firmware using the USB flash procedure. I assume update finishes successfully but the TV behaves the same.

I tried unplugging both back-light power connectors - TV shuts down as described above.
Than I tried plugging in only the left back-light power connector, back-light flashes and TV turns off.
After that I plugged in only the right back-light power connector, back-light doesn't flash and TV turns off.
I measured voltage on both back-light power connectors and after the back-light flash voltege on both connectors is 200V DC.
The back-light flash period is extremely short so I am not able to measure the voltage.

It looks like the right LED strip is broken but I believe that this would not cause the TV to shut off completely.

I have measured 3.3V and 12V on PSU.
All capacitors look OK to me.

I could not find the schematics for the PSU GL10 - so I don't know if 200V for back-light is OK.

Any help is appreciated. Thank you.

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

It looks like the right LED strip is broken but I believe that this would not cause the TV to shut off completely..

you have shorted LED, this why the reading of voltage going high to 200, TV turn off as protecting mode to let the PSU not damage. take screen apart and repair LED

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

Thank you Diah.
I will take screen apart and check all LEDs.

But I think that there might be something else besides the back-light LED short.
I have tried turning the TV on without back-light connected to PSU. TV shuts down just the same.
Should the TV shut down if back-light is not connected to PSU?

Does anybody know specs for LEDs used in this TV?
Is it 3V or 6V, what is the LED current?

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

Should the TV shut down if back-light is not connected to PSU?

Does anybody know specs for LEDs used in this TV?
Is it 3V or 6V, what is the LED current?

of course if the back light socket not plug in the PSU will not detuct them ( like Open LED ) tv will turn off.

take clear close photo on your strips and piece of LED, upload here we will help you with specification

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

I have disassembled the panel.
There are two strips mounted on one aluminum cooler, each strip contains 56 LEDs.
I have tested LEDs using voltage slightly under 6V (there are 5 LEDs broken on one strip, all LEDs are OK on other strip).
I presume that LED voltage is 6V but I found that there exist also 6.2V LEDs.
It seems that supply voltage should be over 336V per strip. I have measured 200V on my PSU.
LED dimensions: 4mm x 2mm
Strips are made by Foxconn (F420LB002-002) - can be seen on one photo.
Bad LEDs are marked black on one of attached photos.

Can you recommend me good quality LEDs?

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

Additional photo of LEDs.
This one is more precise.

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

i think double LED 7030 6V. you can measure on LED 7mm long 3mm wide, take on out of its place and check the down side of it as it had 2 chassis grounded or one,

on Aliexpress you found them for example http://www.aliexpress.com/item/100PC...445357361.html

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

I have measured, LED dimensions are 4mm x 2mm.
I removed one LED, layout can be seen on attached photo.

What temperature should be used for hot air soldering of SMD LEDs?

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

are u sure.. in mm

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

Yes, definitely 4mm x 2mm.
Photos attached.

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

its 7030 6 V mat, you are measuring the long of LED body only, don't forget you have 2 legs on + - down side for soldering

[budm]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

4020 LED: Your width is 2mm. Remove one from the board and verify footprint and pad assignment for the Anode and Cathode.
https://www.aliexpress.com/store/gro...32782be9JIyRoZ

See the spec of 7030 attached, see dimension on page 3.

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

4020 LED: Your width is 2mm. Remove one from the board and verify footprint and pad assignment for the Anode and Cathode.
https://www.aliexpress.com/store/gro...32782be9JIyRoZ

See the spec of 7030 attached, see dimension on page 3.

budm, 4020 surface mount with out soldering bed , look on his leds they have beds left and right

i may wrong,

[budm]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

But the width is 2mm not 3 mm, see LG spec for 7030, the width is 3mm since there is no solder pad to come into play for width dimension, and if you look at the SMD pad (not the PCB solder pad) if you add what are on the LED it will still not come out to be 7mm pin to pin.
Since he already remove the LED, so now he can accurately check the dimension and the pins assignment to be sure before trying to get the replacement, better to be safe than sorry.

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

7mm is larger than LEDs on this strip - photo attached.
I think I could fit 7030 LED if i scoop the white paint from copper.
I found that 4020 LEDs can be found on Aliexpress too, but maybe I should go with 7030 since the quality is probably better.
Maybe I should go with replacing all LEDs? I assume 7030 would last longer than 4020.
What temperature is OK for hot air station when working with SMD LEDs?

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

you are correct with width but if the LED had solder pad then will be not 4mm.
best way he remove one and see the pad exist or not, from photo show it had

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

the one you took it out it had soldering pad on both side + - or not just flat

[Diah]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

budm correct 4020 with out pad. don't go with 7030. stay at original type better to you

[budm]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

Based on this picture, it is not 7030:
https://www.badcaps.net/forum/attach...1&d=1553283312

[zarko]

Re: Sony Bravia KDL-42EX440 - problem - turns off after switching on

Here is a photo of bottom side of LED. No pads.
I will go with 4020, 6V, 150mA.

I have few questions regarding SMD LED soldering, I have no experience with this type of components.
What is the best way to solder SMD LED without pads?
Can I try with soldering iron or I should skip it and go with hot air station?
What is max allowed temperature if I go wit hot air?

Thank you.