EU40F6400 startup failure

[aurelienr]

Re: EU40F6400 startup failure

No picture, no backlight....but sound works and I ear I can scroll into the menu with the remote...

[Davi.p]

Re: EU40F6400 startup failure

There is a remote possibility that the software of this particular model, but is no common on Samsung, switches off the B.L. if it senses a problem on the tcon, that has an i2c bus communicating diangostic to the mainb., so i think since mainb. are expensive, you can troubleshoot tcon, but i need a big picture of it without the shield, i think you use a bad method of posting images, click on the page bottom "post reply" then click on the paper clip, it appears a window , you can click a button to select the path of the image, then click upload, wait for the message then "close window" button, now select the arrow neat paper clip so link the photo in your text.

[aurelienr]

Re: EU40F6400 startup failure

Done

[aurelienr]

Re: EU40F6400 startup failure

I check the tantalum caps (that often fails by creating a short), the black one on the top (marked NEF/EN7) is in shortcut. I could unsolder it to check if this is really the cap of another part that is in shortcut...

[aurelienr]

Re: EU40F6400 startup failure

In a previous post I said that The LED3 was off and on the PCB I see that it is connected to the AVDD plane. It's likely that the cap I measured in short is connected to this plane, explaining why LED is not on. If fuse does not trigger that means there is either a current limiting device (but I did not detected any overheat on any component), or simply that the AVDD power is disabled in software for any reason (short protection for example).

[aurelienr]

Re: EU40F6400 startup failure

I ordered a new cap, I will test it tomorrow...if nothing change, I will try to find a replacement board...

[Davi.p]

Re: EU40F6400 startup failure

Hi, sorry i was doing other things and following an ebay auction (won a broken smart tv!), you better wait for help before ordering parts cause shipping is usually expensive, the AVDD plane goes directly to the panel via connector, so you better try voltages with the 2 flat cables detached, not only, it goes also to the Gamma corr. chip, that is one of the 2 medium chips, 1 on the left 1 on the right (mainb. con. on bottom), so you have to locate with multimeter continuity, which black square diode is connected from the cathode (band) to the positive of the tant. cap (band), done this you must unsolder it and unsolder the cap., then check the cap for short, if it's good connect the diode anode to the board with a wire, just for testing purposes, then the cap + to the diode cathode and the cap - to the GND, now you can test AVDD tension, it must be around 15V. To be sure on which chip contains Gamma corrector, you can, with diode unsoldered, provide about 12v to the avdd plane, if you see a chip that starts smoking then that is the chip to be change but is an hard work, for info got youtube "QFN soldering"....

OR, if you arent able to do theese tests, at least try the avdd voltage with panel disconnected, if is not ok unsolder the cap, if is ok, change tcon.

[aurelienr]

Re: EU40F6400 startup failure

Don't worry i'm freelance electronic engineer I've ordered the part in another scheduled order. But I have a lot of work and I forgot to unsolder the cap to test it alone, shame
Of course the measurement has been done with all cables disconnected.
When powering on, the AVDD was obviously 0 because its LED was off ( but I did not measured it).

[aurelienr]

Re: EU40F6400 startup failure

I have unsoldered capacitor, it is not in shortcut. But on the board I measure a resistance of approx 3 ohms between AVDD and GND. Since you told me I should read about 12V on this plane, that would represent a 4 amp current, I don't think it is a normal current for this board (especially if it comes from the LVDS cable) !
I think I have found a Tcon board for repairing for 30 euros, I will try...

[Davi.p]

Re: EU40F6400 startup failure

"Since you told me I should read about 12V on this plane"
No i've said 15v.. so 5 Amp.

[aurelienr]

Re: EU40F6400 startup failure

I changed the Tcon...still no change, same bug....

[Davi.p]

Re: EU40F6400 startup failure

It's so sad.. maybe this Tcon has something new from older ones that i don't know, maybe some voltages on tcon lacks due to no colour data and/or i2c comm sent from mainboard?
E-ehm... on the post #18 i expressed myself bad, i wanted to say if you see the image pointing a lamp to the screen ' cause backlight is off and you have to provide light externally... i apologyze for that, big error...

[aurelienr]

Re: EU40F6400 startup failure

Not 100% sure of new Tcon functionnality, was sold as functionnal but I can't be sure (only 40 euros on ebay).
The screen is really blanck since, as I said before, I cut one of the PWM line of the cable between MB and PSU, so that the internal pull up resistor on the PSU force one part of the backlight to be on (and it works, but nothing displayed).

[aurelienr]

Re: EU40F6400 startup failure

No idea of what I could do to check MB functionnality ?

[Davi.p]

Re: EU40F6400 startup failure

On the post #5 you listed PSU pin voltages, Capleaker have told you to measure with mainboard attached, but it's not possible that backlight is not ON if the BLU is high, i have in repairation in my house a Samsung 46" led tv, with the same pinout, without main attached the ON signals are pulled high internally. Surely you have a low BLU, then.. why? It's a strange behaviour, really never seen by me, i'm only suspecting again for the tcon since i think there's no subtensions generated on the main that affects only lvds video out and not audio, also a cpu detaching ususally is not all by a shot, therefore it ususally works sometimes or for some seconds at powerup. Maybe i will try to dowonload Serv. manual but i'm too busy and nowadays Sams manuals are very empty of useful infos. Bye.

[aurelienr]

Re: EU40F6400 startup failure

With new Tcon problem still here...µI checked AVDD to GND resistance, it seems normal (several kOhms) on new board comparing to the short measured on my Tcon, but changing the board did not solve the issue.
I already spent too much time on this sh**, I bought a new TV and will try to sell the valid Tcon, the PSU and some other parts on ebay...

[Davi.p]

Re: EU40F6400 startup failure

I hope new tv is not Samsung, which brand is?

[aurelienr]

Re: EU40F6400 startup failure

huhuhu
samsung

[Davi.p]

Re: EU40F6400 startup failure

No way!