samsung le40s71b

[senndogg]

hello.
this 40" lcd tv has a strange behavior.
turns on, makes the usual samsung wake up tone, shows a 3/4 of the screen distorted image for 2 seconds, and turns off. after a second it turns on again with the tone, distorted image, again off. i have the impression that it can do this for an eternity if i do not unplug it.
i did a lot of searches.
all odds got to the notorious samsung power supply, in this case , a BN44-00134A.
it is full of SamWha caps. no one is bulky but i followed the general rules and replaced the 4x 10V/1000uF with new (no name) 16V/1000uf, and a 25V/220uF with a similar one. no effect. i have to replace also 2x 25V/1000uF but i dont have them at the moment. maybe later, but i am a little worried for the image i see in those 2 secs. it looks like a bad ribbon cable, reseated it and when the tv restarts the faulty t-con suspected image is still there.
this tv has been opened before, i dont know who opened it but it stated "a faulty display which costs more than the actual tv value". i guess he might be a little wrong and i have to prove that.
still 2 caps to change, the overall voltages seem ok.
i read somewhere about a small cap responsible for the on/off cycle but i dont know exactly.
i got plenty of time, some skills and a strong intention to fix this tv.
any help would be appreciated.
thanks.

[senndogg]

Re: samsung le40s71b

a fact: the relay clicks only once when plugged in. when it self restarts, the relay doesnt click.

[senndogg]

Re: samsung le40s71b

further investigations:
replaced the 2 remaining caps with 2 known working ones. still that issue.
removed the backlight connector from the main board. so less power will be drained from the psu. the problem still occurs.
when the tv goes on and off the main voltages are ok: 5,08V, 12,12V but the 13V rail fluctuates between 13,33V and 13,01V when it restarts.
i am really suspecting the main board.
after removing the main board noticed that it is somehow hot near the RF unit. now i am supposing this has occurred because of a possible lightning through the aerial and has shortened any component nearby, so when it wants to start it drains to much power and then goes off again. a problem in the main board would be good for me as it would explain the strange image i see when the tv is on for the 2 secs.

[selldoor]

Re: samsung le40s71b

Hi Dont know if you have it but service manual is here http://www.scribd.com/doc/22840588/T...hassis-Gsm40se Typically however it doesnt seem to cover this particular power supply.
One of the many things i dont follow is : The transformer at T1801 appears to feed
to ccfl type connectors. Does that drive all the lamps in a 40" panel or is there another inverter board somewhere?

[Scenic]

Re: samsung le40s71b

Typically however it doesnt seem to cover this particular power supply.

See attachment, allthough I doubt it's a PSU board problem.

One of the many things i dont follow is : The transformer at T1801 appears to feed
to ccfl type connectors. Does that drive all the lamps in a 40" panel or is there another inverter board somewhere?

Those Samsung TVs generate a high voltage on the PSU board (in this case 1500V at 80mA according to the silkscreen markings) which is fed to the inverter board and gets split up, driving the CCFLs. There's usually another control wire thing going to the inverter.

The HV wires (blue and white) are at the bottom left, the inverter control wires at the top left in this pic.
https://www.badcaps.net/forum/attach...9&d=1333383460

@ senndogg: What mainboard model is it? There should be a BN44-... and a BN94-.... number on it somewhere

[senndogg]

Re: samsung le40s71b

thank you for your effort selldoor, but i am not thinking of a psu failure anymore. the voltages are ok meanwhile the tv restarts. i bet it is a main board problem.
the board is BN91-01336A, probably not found in the usa because of region specs i suppose. anyway managed to found boards LIKE this on ebay (from NZ or usa) for 80$.
now, i pretend that there is a power drain from a failed component in the board. at the moment i am measuring the voltages at the regulators. your help is appreciated in telling me if there is anything wrong. thanks.

[senndogg]

Re: samsung le40s71b

scenic is right; the ccfls are fed by a huge transformer in the psu. this has his own mini power supply from the 220V main rail. so the 24/32V doesnt affect the other voltages, i was wrong in this statement "removed the backlight connector from the main board. so less power will be drained from the psu."
as i understand, the little transformer TS801 outputs a 6.5v stand-by power for a part of the main board which controls the infrared receiver and the indicator LED. if there is a command "turn on" there is a return wire, the "P-ON/OFF", which turns on the relay and the other 2 big transformers, the backlight and the 13V one.
right?

[senndogg]

Re: samsung le40s71b

this is the correct version BN41-00680D.

[selldoor]

Re: samsung le40s71b

Thanks Scenic have not seen one of these before.
I was hoping to troubleshoot the back light going off as a 2 sec to black but couldnt see how it worked. I thought if you could get the lights to stay on then you might see better what else is wrong with the panel. Perhaps if you get to it you can post a pic of the inverter/ lamp power distribution board.
As you say if something else is affecting the P-On then it is likely that cutting power off to the big transformer. - I will keep thinking. Budm is good at tracking these faults.

[senndogg]

Re: samsung le40s71b

i dont think it is backlight related. disconnecting the light control connector has no effect and there is no picture in the screen.
also it is not p-on related. it is constant, as the relay doesnt click and the 12V and 5V are continuous. it is something in the main board, till now, checked every single regulator and everything is ok according to the service manual.

[senndogg]

Re: samsung le40s71b

i am afraid it is EEPROM related

[senndogg]

Re: samsung le40s71b

@scenic, i read your thread.
i am thinking of a corrupted firmware too. but i have a different kind of board and different eeprom. also, i have no video.

[selldoor]

Re: samsung le40s71b

Oh dear - not good news. Perhaps the eeprom can be replaced - /reset. I believe Tom66
knows a bit about this there is a recent thread where he was suggesting it but I dont think it was tried.
This might interest you - different set but at least a samsung. Obviously at your own risk
but if you can get some help from the others it may work for you.
http://www.tv.quuq.org/forum/index.p...e;topic=2377.0

[tom66]

Re: samsung le40s71b

I've never needed to do it myself before, but it is common amongst Samsung TVs. That post selldoor linked explains exactly how to do it.

[senndogg]

Re: samsung le40s71b

first of all thank you for your replies, but now i am desperate...
it seems that LExxSxxx uses different hardware than those in the quuq forum.
i followed and traced every power related component in the main board according to the service manual (which i can upload for you) and everything was ok (or at least i think so). i dont even know what caused this problems.
anyway, this one DOES NOT click. there is 6.5V in the power section of the board. you press the power button, the board sends a 5V to the psu to activate the relay and then there is 12V and 5V everywhere where it should be.
all regulators are ok, there is 9V, 8V, 3,3V, 2,5V, and 1,8V in the crucial components. the tv turns off after 2 seconds and then on again with the samsung tone. the 12V and 5V stays there as the relay is activated.
another hypothesis is t-con related.
when the tv is on, during those 2 seconds there is no sound but only a strange figure shown in my first post. i suppose the t-con is faulty and the restart is a self diagnose where the main board connects to a faulty t-con. it also restarts when the lvds is disconnected.

[senndogg]

Re: samsung le40s71b

and, as you see this board uses another kind of FLASH/EEPROM.

[senndogg]

Re: samsung le40s71b

UPDATES.
read further about the non-clicking-restart-problem and looked for the eeprom. my friend who has programmed many chips with his Elnec bee-programmer bets that the IC903 is the eeprom chip. so i tried the pin5-6 trick.
nothing happened when shorting for 2 seconds. but when shorting for more than 5 seconds the tv would not restart anymore. strange. the pattern shown in screen also changed. but at the moment when pins5 and 6 are not shorted the tv still restarts in 2 seconds. anyone has any idea what has happened?
now i have access to the t-con. later i'll do some measurements.

[senndogg]

Re: samsung le40s71b

all t-con voltages ok. 5V, 3,3V, 1,8V, 26V, 15V.

[Scenic]

Re: samsung le40s71b

The EEPROM in question on the affected Samsungs is a 256KBit one, usually made by Atmel.
They either have "(AT)24C256B" or "2EB 1" in the 2nd line.

Messing with the wrong EEPROM could cause even more problems..

[randtek]

Re: samsung le40s71b

have you tried disconnecting the LVDS cable to the TCon board to see if the power will stay on? I have located bad TCon boards on samsungs with this technique before.