Darn need help guys samsung ln-t4042h 24v backlight problems

[davewilson61]

HI GUYS
SAMSUNG LNT4042H

Plug in relay clicks waits 10 seconds clicks again every 10 seconds led on front blinks 5 time

found 1 bad cap but changed 7 of the larger caps by the bad one
check all voltages seem to have them 5v 12v ect
only one never present at any clicks is the 24v for the backlight inverter even unpluged the board from the ps and still no 24v on the ps connector.. stays at 0v ....

i guess the tv is cycling over and over looking for the backlight to come on..

cant find the 24v section on the schematic ? strange...ELEktro or tgohome


thanks if you can help ...dave ...can have pics up in 10 min if needed

[tom66]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

What capacitors did you use as replacements?

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

nte the bad one and 6 others

[notallbad]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

Not familiar with the set and no schematics provided so is there a pin marked BL_On? Normally reads around 3v. This is the signal which returns to the PS to provide the 24v for the inverter.

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

some picks

[notallbad]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

Any voltage on Pin 1 at CN1803?

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

iteresting above cn1803 it says inverter on/off above the 7 capasitors i replaced
maybe the main board is not turning on the inverter...wonder if i could jump it..guess i could check it for volts...powered on and off ?

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

would that bl be inverter on/off pin...ill check for the bl ....be right back

[notallbad]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

would that bl be inverter on/off pin...ill check for the bl ....be right back

BL_On - Back Light On

It may be that on power up the PS provides 24v to the inverter, the inverter then powers up and sends the 3v BL_On (Inverter On) signal to the Main board.

[notallbad]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

Get some really good close up images of both sides of the PS board.

Look for any dry joints on the solder side of the board too! Especially around the Transformers.

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

ok cn1803
1 0.02v relay goes off and on no change
2 3.34v
3 0v
4 0v
5 5.38

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

getting them close ups

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

pics up...cant find anything BL

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

did check the inverter for power up dead 0v always not even a spike in volts

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

think i should jump 5v to pin 1?

[tom66]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

Pin 1 is PSON?
On some Samsung it is supposed to be low to turn on.

[notallbad]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

Is that Pin 1 CN?01 Power On/Off?

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

cn1803 inverter on/off... its at 0.02v always add 5v? would turn on backlight no?

[davewilson61]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

pin 1

[notallbad]

Re: Darn need help guys samsung ln-t4042h 24v backlight problems

think i should jump 5v to pin 1?

Yes, that would prove the PS is alright if the inverter kicks in with 24v supply and that the inverter board is good if it gives a 3v Inverter On signal.

So fault will be with the Main A/Vboard.