Samsung LE32D400E1W no backlight

[toty79]

Hello to all friends of the forum and well found, I ask help to you more experts to be able to repair as mentioned the above mentioned samsung tv with backlight problem, model Samsung LE32D400E1W with U57E chassis, I have owned the tv for a few years, the last times the backlight flashed cold and then stabilized immediately afterwards, unfortunately now the backlight does not turn on even a flash, audio ok and image present if I point a light on the display, at first I thought it was a problem with the inverter SST320_4UA01 but after having carefully checked I realize that two voltages from the power supply BN44-00438A are missing
* of which I attach the services manual, this power supply has incorporated a part of inverter, the missing connections appear to me on the connector CNI801 called HIGH (fet) and LOW (fet) both at 0v but I report more precisely all the voltages on the CNI801 below

CNI801

pin1) high fet = 0v
pin2) nc
pin3) low fet = 0v
pin4) nc
pin5) nc
pin6) nc
pin7) nc
pin8) GND
pin9) OVP = 0v
pin10) CNT-PRT = 12,15v
pin11) VCC = 12,80v
pin12) LD = 11,40v

I am measuring voltages on the CNI802 and will report them shortly, thanks to all those who will participate in the discussion ...

[toty79]

Re: Samsung LE32D400E1W no backlight

Here are the tensions on CNI802 which goes to the main, in blue the detected tensions that seem to be all normal, any suggestions and well accepted, at first glance no obvious signs, retouched some welds without result, no short circuit in appearance on mosfets and diodes on the surface, dc voltage on mains filter capacitor 390v stable, thanks to all

[budm]

Re: Samsung LE32D400E1W no backlight

Please attach good clear straight shots of the whole top and bottoms side of YOUR board for us to look at.

[toty79]

Re: Samsung LE32D400E1W no backlight

Thanks budm for joining us, here are the photos I hope will go well

[budm]

Re: Samsung LE32D400E1W no backlight

Where are the whole backside of the TV showing all the boards?

[toty79]

Re: Samsung LE32D400E1W no backlight

Sorry here they are, thanks

[budm]

Re: Samsung LE32D400E1W no backlight

1) I assume that the fuse next to the black main filter cap (450vdc CAP) tested OK, corrected?
2) What is the DC v when measure between the two legs of the main filter cap when TV is turned on? 380 ~ 400VDC?
4) The inverter transformer drive output will be very high frequency AC which will be too high of the frequency for your meter to read, it may or may not show any activity.
5) You may want to read these threads since they are referring to the same power supply/Inverter transformer driver board.

[nomoresonys]

Re: Samsung LE32D400E1W no backlight

With tv unplugged from power, unhook cable from powerboard to mainboard, leave it off, plug power cord back into powerboard, do backlights come on and stay on?

[toty79]

Re: Samsung LE32D400E1W no backlight

Thank you all

budm
1) yes tested and everything ok
2) Filter cap voltage at tv on 390vdc stable
4) Ok if it can help I also have a small oscilloscope, the more I have the less I know how to use it but using it with your indications would be ideal .. thanks
5) I read several threads on the forum, even on different TV models with the same power board but no solution

nomoresonys
I had just read a discussion on the forum, this power supply starts even without the main connected, I did the test as described, the power supply turns on delivers all the voltages as in post N1 and N2 but the lamps remain off

[nomoresonys]

Re: Samsung LE32D400E1W no backlight

Ok, looks like a backlight issue, bad led/s or connection, more than likely.

[dick_barton]

Re: Samsung LE32D400E1W no backlight

What voltage do you have on Pin 16 (EN) of UI801 (SEM2106)

Have a read through https://www.badcaps.net/forum/showthread.php?t=32636

[toty79]

Re: Samsung LE32D400E1W no backlight

nomoresonys
the TV and an LCD with CCFL lamps would avoid a problem with the lamps as it has a few hours of work, I would get to them by opening the panel but only as a last resort

dick_barton
I countered the tensions on UI801 (sem2106) and here they are


pin1) 0v
pin2) 0v
pin3) 0v
pin4) 0v
pin5) 0v
pin6) 0v
pin7) 0v
pin8) 0v
pin9) 0v
pin10) 0v
pin11) 0v
pin12) 0v
pin13) 0v
pin14) 12,80vdc
pin15) 4vdc
pin16) 5vdc
pin17) 0v
pin18) 0v
pin19) 0v
pin20) 0v
pin21) 0v
pin22) 0v
pin23) 0v
pin24) 0v

as you can see SEM2106 is powered with vcc and enable signal, but almost all the remaining pins indicate 0vdc, could it be a defective ic? have I not piloted? I read the thread suggested by dick_barton where they complain about problems with some zener diodes, I will do a test to see if any zener diode is short, thanks for all the suggestions

[nomoresonys]

Re: Samsung LE32D400E1W no backlight

Lol, oops my bad, didn't look at the picture, there's the inverter board big as life, definitely not an led tv.

[nomoresonys]

Re: Samsung LE32D400E1W no backlight

Look that inverter board over real good, did you check the fuse on it?

[dick_barton]

Re: Samsung LE32D400E1W no backlight

I think Vref Pin1 (SEM2106) should be 5.0V according to another forum. I am suspecting the SEM2106 as being faulty.
It would be worth checking QI801 and QI803 and also mosfets MI801S and MI802S

This is from another forum:-

the TV turns on, there is no backlight. two transistors mi801S and mi802S were punched on the power supply unit, after their replacement the backlight did not appear, voltages n1 and n2 do not appear on the PWM sem2106 controller.
1st leg vref - 5v
14th foot vcc - 12.5v
16th leg en - 5v

[toty79]

Re: Samsung LE32D400E1W no backlight

I confirm pin1 (sem2106) vref and 0v like all the restantins of the ic except the 3 pins described in the previous post, checked with the multimeter the diodes mentioned in the post of the user kleini which ZDI805-ZDI804-ZDI801 whose with the multimeter not I am in short circuit, another test I did but I don't know if the measurement could be correct and this black test lead on the frame and red test lead on the cathode of the 3 diodes described above with the following results

katode ZDI801 = 4.95vdc
katode ZDI804 = 1.7vdc
katode ZDI805 = 4.05vdc

Can Measures Help Detect a Failed Diode? all suggestions well accepted thanks
*

[toty79]

Re: Samsung LE32D400E1W no backlight

Fixed friends and thanks to everyone

replaced sem-2106 with one from recovery the tv returns to work perfectly, thanks

[nomoresonys]

Re: Samsung LE32D400E1W no backlight

Nice job, Dick nailed that one.