EU40F6400 startup failure

[aurelienr]

Hi guys
I have a a EU40F6400 TV and when I was watching a movie suddenly image became black, but sound was ok. After restart, same problem, and I noticed that the power LED was blinking 5 times at startup before shuting down (but sound still present when I press the remote control).
Then I have open the TV to look at the PSU, ref BN44-00622B.

Both fuses are tested ok. Relay is ok.
No traces of any damage on both board faces.
All the capacitors seems like new !

I get the schematics here :


For the moment, I have checked the voltages on the backlight connector (and directly on the output caps). This is what I measure :
C9154 : 40V (schematic specify 43V)
C9254, C9354, C9454 : 95V (schematic specify 85V)
Same measurements with either the backlight cable connected or not.

I'm not sure if I should order a new PSU (100 euros) or not. Since caps are ok (voltages measures on all others caps seems valid, approx 5V and 12V respectively), what kind of failure could I suspect ? Would it be possible that the error come frm the backlight ? It should be wired because it seems to have 4 backight power lines, all the sections failing at the same time is unusual...(but I'm not sure of backlight composition).

Thanks !
Aurelien

[CapLeaker]

Re: EU40F6400 startup failure

Plug in the backlights to the PSU and unplug the main board from it. Plug the PSU into mains and the backlights should turn on.
IF they don't:
Check the LED voltage on EACH string at the PSU and report the voltages measured. I think you have a backlight problem at the LED's. I am not convinced (yet) that the PSU is at fault. Also upload some high resolution, straight shot pictures, please.

[aurelienr]

Re: EU40F6400 startup failure

Hello
Thanks for the advice.
I made your test and backlight is on, as you can see on pictures.
However I noticed a small black round on the screen (circled in red on the photo, the other shadows are myself and a lamp), but since this is an edge LED backlight, I don't think it comes from a LED failure ?

EDIT : maybe the circle shadow come from a small plstic piece that falls under the matal plate (you can see a high light spot where the piece was placed)

Tell me if you need more pictures.

Aurelien

[CapLeaker]

Re: EU40F6400 startup failure

Plug in the main board to the PSU and turn the TV on. Measure the DC voltages on each pin of that connector and post it here in a format of pin#, pin name, voltage measured.

There is somewhere a pin called BLon (comes from the main and tells the backlights to turn on), also DIM etc. Let's see what these voltages are...

[aurelienr]

Re: EU40F6400 startup failure

So :
- 5V is present on A5V and B5V pins
- 12.6V is present onVamp and B13V pins
- the EPWMx pins are all at 0
- the PS_On/Off is at 3.3V
- the OD_On/Off is at 3.3V
- the BLU_On/Off is at 5V

Mother board ref is BN41-01958A

Aurelien

[aurelienr]

Re: EU40F6400 startup failure

Looks like MB does not handle PWM signals correctly, but why ?
The signals that come from PSU to MB are only power supplies that are good (5V and 13V). So MB does not generate correctly the PWM.
It may be either an hardware issue on the PWM generation, or a problem with the source that determine the PWM power. Is there any ambient light sensor somewhere ?

[CapLeaker]

Re: EU40F6400 startup failure

Could you upload a high resolution, straight shot picture of each board?

[aurelienr]

Re: EU40F6400 startup failure

Here we go...
https://we.tl/PcDVyCZ1h2

FYI, the MB<>PSU cable and connectors/contacts are not damaged.

[aurelienr]

Re: EU40F6400 startup failure

Should I be able to see a very low image without backlight ?
I'm tempted by cutting one of the PWM signals to enable one of the backlights outputs and see what is displayed...if the problem is due to a memory problem I may be able to perform a factory reset ?

[budm]

Re: EU40F6400 startup failure

When you test the power supply/LED driver board by itself and the backlights stay on, the you should look at the PWM control signal to see what it is.

[aurelienr]

Re: EU40F6400 startup failure

According to the schematic, there are pullup that should set them high, but I will check !

[aurelienr]

Re: EU40F6400 startup failure

I made the measurements. When MB disconnected, the PWM signals are at 3.3V level and BLU_On/Off is also high.
I tried my idea of cutting the PWM4 wire and reconnected MB, the TV starts with the bottom backlight enabled, but nothing is displayed on the screen. However, I can go into the menus, I ear the clic sound of volume up/down, and when I select the "smart hub" function I get the other sound made when I scroll up/down in the selection.
Would it be possible that the Tcon board fails, so that the MB disables the backlight that becomes useless ?

[aurelienr]

Re: EU40F6400 startup failure

Picture of the Tcon board. Only two LEDs on, LED1 and LED2. LED3 is off.
https://we.tl/jR5XeUJN7Y

[CapLeaker]

Re: EU40F6400 startup failure

The main board should power up and the backlights on even without the TCon being plugged in. Please upload the pictures using the attachment function to this site, not some offsite, as pictures disappear after a while.

[aurelienr]

Re: EU40F6400 startup failure

So... no idea of the problem origin ?
What should I do ?
If a buy a motherboard for repairing, should I take care of both the MB model AND the TV model to be sure to have the correct firmware inside ?

PS : for photos, my picrtures were too heavy for the forum

[CapLeaker]

Re: EU40F6400 startup failure

The new main board has to be compatible with your TV. Sometimes there is more than one main board. Sometimes you can "upgrade" a TV by putting in a better board. All depends on what you want to do.
As far as the origin of the problem... I guess you need to trace that back on the main board.

[aurelienr]

Re: EU40F6400 startup failure

Easy to say, without schematics and knowledge of software behavior
I will try to reflow BGA, then go to garbage and try to sell some spare parts...only 4 years old, what a shame !

[Davi.p]

Re: EU40F6400 startup failure

Hi, first your model is UE40F6400 (not EU..).. then a bad troubleshooting method has been followed, the first thing to do was to see with a lamp if you see the image without backlight, if you don't then the major clue is tcon bad, second you must read the pin assignment of the PSU<>main connector, if there's not a line called ER-something or the like, then you don't have an error signal that tells the mainb. you have a backlight problem, so it is not possible led blinkings. To troubleshoot tcon first check it's input fuse.

[aurelienr]

Re: EU40F6400 startup failure

the first thing to do was to see with a lamp if you see the image without backlight

Already done, no image. Then, as I said before, I cut one of the PWM wire from the mainboard to force one string to light on (through internal pullup on PSU), and still no image visible.

if you don't then the major clue is tcon bad, second you must read the pin assignment of the PSU<>main connector if there's not a line called ER-something or the like, then you don't have an error signal that tells the mainb. you have a backlight problem, so it is not possible led blinkings.

I read the schematics (link in first post) and there is no error/status/feedback signal, so yes the problem comes from the MB or the Tcon...PWM are generated from MB, but if there is no picture I would guess that there is a problem with Tcon only, but someone on the forum told me that if Tcon fails the backlight continues to operate. Is it a wrong statement ?

To troubleshoot tcon first check it's input fuse.

Fuse is ok, moreover the LEDs are ok on the Tcon board.

[Davi.p]

Re: EU40F6400 startup failure

"if Tcon fails the backlight continues to operate. Is it a wrong statement ?" No is correct, i have forgot this, so are you sure with all hooked up you have no image - no B.Light? This is the first i have seen..! This carries me to a mainboard problem.