Samsung 40inch lcd tv backlight goes off sound good

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

mine is bn44-00134a

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

wrong post.

[budm]

Re: Samsung 40inch lcd tv backlight goes off sound good

OK, this board does not have pull-up resistors based on the diagram (not from SAMSUNG) so disconnecting the cable on this one will not cause it to come on.
You will have to measure the Voltage on all the pins on the power supply board that goes to the main board when the TV is working and when the TV does not work to see if any of the signals are missing or not.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

i checked all the voltages on all the wires on power supply when backlight went off and all are good

the only wires i didnt check were the ones from large transformer

[budm]

Re: Samsung 40inch lcd tv backlight goes off sound good

What do mean by all good? what are the readings?
The ps_on, the bl_on, the dimm, are good? The PFC Voltage is good?

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

im at work but on all the voltages where there is a number i get same voltage

i get 12v 12v 12v 13v 5v 5v etc etc etc...on all pins marked on the large cable going to main board

not sure about bl-on and dimm values will check afer work

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

heres a good pic. of the board. http://www.shopjimmy.com/samsung-bn4...wer-supply.htm

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

mine has backlights, just cant figure out which component/s on mainboard is bad.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

all check good see photo

[budm]

Re: Samsung 40inch lcd tv backlight goes off sound good

im at work but on all the voltages where there is a number i get same voltage

i get 12v 12v 12v 13v 5v 5v etc etc etc...on all pins marked on the large cable going to main board

not sure about bl-on and dimm values will check afer work

Well that is why saying they are OK means you know what all the Voltages of all the signals and supply should be, but you do not have no bl_on = no backlights, no PWM DIM = no backlights.
You have to understand what the TV needs to get the backlights to work.

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

pic. of mainboard. http://www.shopjimmy.com/samsung-bn9...main-board.htm

[budm]

Re: Samsung 40inch lcd tv backlight goes off sound good

all check good see photo

There are two set of cables that go to the main board.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

yes the other set has no voltage number labeled.....when i get home i will check voltages when tv works then when backlights go off i will check voltages....

thank you

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

this set has bad history on bad caps in that area but all caps look good....sometimes the backlight will stay on for hours...sometimes 5 minutes.........ill let u know tomorrow my results

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

well why am i getting 12v to the two thin boards from the power supply even when the backlight goes off....? whats the purpose of the 12v present?.....obviously it doesnt power on the backlgiht correct?

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

backlight usually need 24v?

[nomoresonys]

Re: Samsung 40inch lcd tv backlight goes off sound good

probably wouldnt hurt to touch up those solder joints you spoke of.

[budm]

Re: Samsung 40inch lcd tv backlight goes off sound good

"backlight usually need 24v?"
"well why am i getting 12v to the two thin boards from the power supply even when the backlight goes off....? whats the purpose of the 12v present?.....obviously it doesnt power on the backlgiht correct?"

Not in this Power supply-inverter board combo, the inverter circuits that drive the large High Voltage transformer runs on 380~400VDC which is generated by the PFC Voltage booster circuit.
The older design that has inverter board by itself runs on 24VDC.
The 12V to the balancer boards is for running the sensing circuit that detects if the one or more lamps do not stay on or not connected or draw too much current which then the board will send out an error signal back o shut down the inverter circuits.

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

oh ok.....thanks....maybe the solder joints are bad trwnsformer like you tube video and when that area heats up they come aprt and backlight goes off....if i wait a few minutes with tv off it will power back up with backlight fine ...........it always works when sitting for a while.and powered on.....but once on, backlights will shut off after random time

[shelby5041]

Re: Samsung 40inch lcd tv backlight goes off sound good

yes i saw one video for this tv that when a lamp draws too many amps it will shit down all power to backlights......however not sure thats my case...becuase mine is intermittent if mine had a bad lamp it should trigger all the time same time..probably at startup.....corrrect?......reminder i am very novice so please understand that whan i make responses.........i am not highly knowledgeable like you on this subject