Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

hah thanks yea i really do want to know everything

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

"Second test With power would be to check the voltages on the pins to see
if they are within the parameters on the datasheet."

i see Vds =40v and Vgs = 20v
so Black probe on Source and red probe on Drain i should see 40v?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

i did the other half of the resistance testing and they turned out more or less the same as the first half. so resistances are all good. none of the mosfets are shorted. now moving onto the scary part (testing voltages)

so if im reading the datasheet correctly these IC's are actually 2 mosfets in one, a N channel and P channel

the N channel is given by D2 S2 and G2 ...there are 2 D2's though...i wonder why there needs to be 2 drains? is it just redundant?
the P channel is given by D1 S1 and G1

for Vds
according to the datasheet i should get 40v when measuring on the N channel and -40v when measuring the P channel
but i get 24v on the N channel, and .14v on the P channel ... i tested a few mosfets and they were all like this.

for Vgs
according to the datasheet i should get + or - 20v
on the N channel i get .52v and on the P channel i get 0v

this is the same for all the mosfets. so ...do i have a problem here, or am i reading the datasheet wrong, or is it the wrong datasheet?

[selldoor]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

The voltages given in the datasheet are absolute maximums that it can handle.

If you watch this
http://www.youtube.com/watch?v=Te5YYVZiOKs

You will see an N channel mosfet is really an electrically operated switch.
It is going to turn the 24v to the inverters on/off depending on whether a voltage is applied to the the gate or not. I am not sure what the P channel
does - perhaps provides a control. Need someone to explain it unless you can google it. Anyway the N channel is never going to produce more than 24v
as that is what is fed into it.

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

yes that makes sense it couldnt go above 24v...i dunno what kinda magic i was expecting a mosfet to do but i get it now
so 24Vds is good? and it only takes .52v to turn it on? why am i not seeing any voltage at the pins of the transformers then?

also it seems like the P channel is not being used to drive the transformers. maybe it doesnt even matter?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

er...so if the mosfets are good, the fuses are good the 0 resistors are good, the board is getting 24v... but transformers are not getting it. should i be able to measure volts on the pins of the transformers? dont they convert it into some kind of super high voltage that alternates?

[selldoor]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

why am i not seeing any voltage at the pins of the transformers then?

That is what I am struggling to understand - what voltage shows on the primary winding posts on an inverter transformer- test for ac as well I have been trying to find how these work but failed so far
I think it will be AC in but high frequency so you cant measure with a multimeter - needs an oscilloscope?

I am not even sure what on the board makes it ac if it is and if a transformer is ac out id expect it to be ac in.

CARE do not test for voltage on the secondary posts - will blow your meter up. 2000vac!!

We need help from budm or bammbamm or anyone who really understands this stuff. ai sometimes think I do then something crops up and I realise
I havent a clue !!

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

ahh yes but knowing what you do not know is the first step towards knowing it

yes i think i was afraid to test the transformers for volts because of that. maybe i never really did test em. ok so the primary winding might be safe to test (input) but the secondary windings are the output which is 2000v. this might seem an easy question but how do i tell which are the primary windings and which are the secondary?

[budm]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

It depends on how the primary side is driven, it cab be driven with half bridge, full-bridge. It is also driven with high frequency pulsing DC so your meter cannot show you the reading if it is switching.
You can make a high voltage probe to see if the high voltage is even present for second when TV is firts turn on.
https://www.badcaps.net/forum/showth...x+dx-40l261a12

[selldoor]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

this might seem an easy question but how do i tell which are the primary windings and which are the secondary?

Thought that had been covered - perhaps another thread. In this case yes it is an easy question (but not always)
http://lcdparts.net/TransformerDetai...ProductID=3497

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

yea i did make that probe and it wouldnt light up on any of the transformers...but i didnt try doing it only for the second after it turns on... ill try again...so do i probe the primary side, the secondary side, or both?
and another stupid question:
the primary side is low voltage and the secondary side is high voltage?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

ok well i tried both sides and i still get nothing...
so i tried it on another TV i have that has good working backlight, and i still cant get the CFL probe to light up. on this tv with the working backlight, i saw some small purple spark where i touched the probe to the transformer pin, and then the backlight went out. luckily turning the tv back on, the backlight came back...but for a moment there i thought i had ruined something. so... am i doing this test wrong? i dont see much room for error here...just solder a wire to the end of a cfl bulb and probe the transformer pins, right? does it have to be only for the moment when the backlight turns on or should it work at any time?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

so um.. what else can i try? why is my cfl probe not working? ideas anyone?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

have we given up on this one?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

should i just order a replacement inverter board? im stuck here and without any further help, the TV is just taking up space in my living room... seems like no one cares anymore... was it something i said???

[Caleb]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

did you have the bulb unplugged? if the system senses that one of the bulbs is drawing more amps than the others it will trigger a shutdown. you should be testing with the bulb on the secondary side of the transformers. Your best bet may be a new inverter board however you may have a bulb that sometimes wont fire up in which case the inverter wont do any good.
I think everyone is just busy with summertime, I havent had much time lately to work on tvs, still trying to get all my firewood cut split and stacked in the shed.

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

ok so i should have one of the bulbs unplugged (related to which transformer im testing) when i use the CFL test? what if i unplug all the bulbs?

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

huh. so the TV's been sitting almost a week without any other ideas, so i went to re-do the cfl test thinking maybe i did it wrong or something and before i could get to it, i turned the TV on and all the backlights came on and everything is working again. so um.. great! but this is also what it did when i first bought it. so im crossing my fingers but i feel like its probly only going to last a day like the last time...

[Caleb]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

I feel your pain I've got a 40" Samsung that I have worked on off and on over about a year. Replaced the inverter and all the ccfls and it still doesn't want to stay on, win some lose some. Every time I get to feeling stupid I get one that I fix within a few minutes of cracking it open. That usually makes me feel better.

[triplefour]

Re: Samsung LN-T3242H works fine for a day, then wont turn on. intermittent.

yea im happy ive been able to fix a few myself but WTH is going on here? update: it was working today for about 4 hours and then kicked off again. cant get it back on. gonna try the CFL test again soon as i eat something