Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off


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Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off

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70JUDGE
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Jul 25, 2010, 4:10 AM

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Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off	Can't Post

When I received the TV it wouldn't turn on.Just had the standby light.I replaced a few capacitors on the power supply board.The TV worked fine until I put the back cover on.Now it will turn on,show a picture for a few seconds,then turn off.I have tested the rest of the capacitors on the power supply with a ESR meter,and they all measured alright.I resoldered the transformers on the backlight inverter.I also tried to test the backlight inverter coils with a multimeter,but I don't know what the readings should,or shouldn't be.They have four legs on one side,and five on the other side.Two are soldered on one side,and four on the other side.I also went as far as to look at all of the backlight bulbs,and didn't see anything wrong with them either.I did try to use a working monitor to test the bulbs,but it did the same thing as the TV,shut off after a few seconds on all of the bulbs.Is it because the bulbs are not the same size?The monitor could sense the wrong bulbs?I did notice a piece of trace missing on the bottom of the power board that I fixed while replacing the bad capacitors,and two wires missing marked on the main board as GND,and CON2 that go from the mainboard to the backlight inverter.It worked with these two wires missing,so I didn't think that could be the problem.I have searched around for for other things to try,and tried some of them,but I have question as to if some of them apply to my TV,or not.Below are some of them,along with why I have question with some of them.Any help is greatly appreciated.Thank You very much!
Tyler
P.S.The power board is a VP212UG01 Ver:4.2,and the backlight inverter is a VIT71009.90(91)(50) Logah Rev:0 AUO P/N:19.26006.111.
1.Can you measure surface mount ceramic capacitors with an ESR meter?I measured some on the bottom of the power supply board,and some measured 30 ohms,and some didn't show on the scale at all.
2.How do you determine what the value,and voltage are for the surface mount ceramic capacitors,and if they are multi layer with no markings on any of them?
3.I measured the transistors/rectifiers that have the heatsinks attatched,and the ones on the power cord side measured fine,but the ones on the output side caused the meter to beep on the two outside pins.One even caused the beeping on all three of the pins.I read that if a coil,or capacitor is near,it would cause the bad readings.

jts1957
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Jul 25, 2010, 6:39 AM

Post #2 of 17 (6678 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

1) ESR meter is for checking ELECTROLYTIC CAPACITORS - try to measure a piece of wire with an ESR meter. Any low ohmic value across cap under test can skew results. Best to test out of circuit.
2) Service literature would be one way.
3) examine the foil side of board, I think you'll find the two outer pins connected by a trace. The one beeping between all three pins I'd check out of circuit. Assuming you are correct in that they are transistors/rectifiers and not MOSFETs or ICs...

How long did the set run before you put the back cover on it. Also: How does the TV perform NOW with the back cover OFF?

Backlight circuitry is a balanced system, if even one thing is off, it will sense it and turn off. Now having said that if you have 8 lamps, 8 pairs of transformers, 8 driver dual MOSFETs etc., each should test like the others. Two pins of one transformer should measure very close to the same two pins of all the rest. It's usually the lamp side of transformer that fails.

If you unplug ALL 8 bulbs and try to start the set plugging in one bulb, you should get a WHITE flash. Unplugging that bulb and plugging in the next should result in another white flash. Continue until all 8 have been tried. If any fail to flash, that channel should be tested further. All bulbs should flash with the same white intensity along the full length of the bulb (it helps to be able to see the whole bulb). If any flash pink or red - bulb is bad.

What are the two sizes of bulbs you have? I work mostly with computer monitors, so I'm most used to 2 bulbs at top & 2 on bottom. I've powered up to approx. a 22" bulb with a 17" monitor chassis.
You can test bulbs with a working monitor or you can use known good bulbs to test in your set.

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(This post was edited by jts1957 on Jul 25, 2010, 6:41 AM)

darrenz
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Jul 25, 2010, 11:38 AM

Post #3 of 17 (6672 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

judge these new tvs are wacky.... i bought a vizio off a lady for 40 that she said didnt work.i brought it home and it worked for about 16 hours,i was turning on,off,on, off before i could get it to show any symptoms.ended up being inverter. i now always test these with audio and video connected to them.these things all turn on diff ways so sometimes ppl think they arnt turning on at all when they really have audio and no pic.and with this trutech they show red in standby and no light when turned on.so if light goes out when turn on ill bet you have sound but no video.its sometimes a challenge when you dont have a screen to look at though to make sure your on right input. your tinkering may have tricked you into thinking you had repaired the problem when that wasnt really problem(that may be why started working then didnt) they will play tricks on you. and these boards will have spots of missing componets as those components are used on a diff model.

70JUDGE
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Aug 6, 2010, 5:54 AM

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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Sorry I haven't written in awhile.I did get to test a few things.When the TV is on I get a little over seven volts on the signal wire that goes to the inverter,but it goes to zero volts when the TV turns off with no sound,or picture,but the standby light is still off meaning the TV is still on.I don't remember if the volts were AC,or DC.If I leave the TV unplugged overnight,and turn it on the next day,it will stay on for about thirty seconds.When it turns off,and I turn it back on it will stay on for maybe ten seconds,and it gets to the point where it will only stay on for a second,or two,but it's not the same everytime.All the time it is on,I get a perfect picture,and sound.The real kicker is,sometimes if I'm not quick enough turning the TV off after it turns off by itself to get the standby light to turn on,I have to unplug it,and plug it back in to get the red standby light to turn on again.I hope that makes sense.I have replaced all of the larger capacitors on the power supply except one.It measured fine on the ESR meter,but so did one of the bulging ones.What are the odds that a capacitor measures good on the meter,but be bad under load?It almost acts like something is overheating.Not enough paste on the transistors?I thought about getting an infrared thermometer,and some freeze spray/component cooler,and see if that might help.I also noticed that the standby light/remote sensor board wires were pinched a little but they worked fine.I even went so far as to unplug them,the speakers,and the TV tuner thinking that the bent plug on the tuner might be shorting out,but it didn't help any.With the back on,or off it doesn't make any difference.Before I put the back on,I really didn't have the TV on long,just long enough to go through a few channels,and see that it worked,so I really can't say if the back had anything to do with it.The part that was making the constant beeping on my meter testing it is a MBR4045PT.The bulbs are the width of the TV,and are u shaped.They all flashed white when I tested them in the TV.Will a ESR meter test the surface mount aluminum capacitors?The ones with the plastic base.Are those considered electrolytic?Thank You very much!
Tyler

jts1957
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Aug 6, 2010, 7:28 AM

Post #5 of 17 (6634 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

When "you" turn the TV "on," the signal wire (assuming signal = enable), as you call it, should give you seven volts. The back light then should flash on and you should obtain audio, then back light turns off. All this time it should STILL read seven volts. All this time set should have audio. When "you" press power to turn set "off" then both audio and enable voltage should quit. Is this occurring?
It will either be a bad inverter board or control board and how the enable line behaves will determine which.
MBR4045PT is a Schottky Rectifier. You should be able to measure its two diodes by removing it from the circuit and then connecting a DVM, one lead to its center pin and the other lead to each of its end pins then reverse polarity of the meter leads. As I stated before I'll bet those two end pins are connected together by a foil on the PCB.
While you have it removed, test between the center foil and the end foils. If you get a very low reading, you'll need to find out what's causing it.

Quote

Will a ESR meter test the surface mount aluminum capacitors?The ones with the plastic base.Are those considered electrolytic?

Possibly. I'd need to see one.

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70JUDGE
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Aug 6, 2010, 8:11 AM

Post #6 of 17 (6631 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

When I turn the TV on,everything works like it should.I have picture,and audio.I get seven volts on the signal wire all the time that the TV is on,but as soon as the TV turns off by itself,the voltage on the signal wire goes to zero.The standby light is off,which means the TV is still on,or unplugged.If I hit the power button after the TV turns off by itself,it lights the standby light up,which means the TV is off.Red standby light means the TV is off.No standby light means the TV is either on,or unplugged.Would a bad bulb cause this,or would it not stay on that long?That,and don't the bulbs show pink,and flicker when they are bad?I hope this helps.Thank You very much!
Tyler

jts1957
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Aug 6, 2010, 9:06 AM

Post #7 of 17 (6629 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Going to Inverter:
1) IF this wire is the enable wire from the control board, the board is turning the inverters off. If you have an adjustable DC power supply, you could provide your own 5-7 volts.
2) There should be a second wire that will adjust the back light intensity.
3) A ground wire.
4) And a B-Plus wire.
Some of these make use more than one conductor/pin.

The fact that your LED light is not behaving as it should and that the set "locks up," also hints at control board.

Does your Inverter board use a C3 and C4 (220�fd 16Volt)?

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70JUDGE
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Aug 7, 2010, 8:37 AM

Post #8 of 17 (6620 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

I took the inverter out,and looked over the coils a little closer.There were two that looked like the tape around them was white.I thought they were bad,but they tested fine.
The inverter doesn't have two 16V capacitors,it has four 35V ones.The inverter is a Logah brand.
As far as the wires,there were four of them,but someone cut the two ground wires off.The other two are the backlight on/off,and the brightness.
After I put the inverter back in,I took the heatsink plates off,and looked at the power supply a little closer,but didn't find anything different,so I put it back together.
When I went to test the TV out,it stayed on longer then it ever has.A little over a couple of minutes before it turns off by itself with no sound,or picture,and the standby light off.I thought maybe it turned on so long because I might have put presure on the coil terminals testing them,and it turned off because the cable wasn't hooked up?After that,I turned it back on again,and it stayed on until I turned it off a minute,or two later.Next,after I put the back on,and hooked it to the cable,it stayed for what I'm guessing a half hour,then it turned off while I had it on mute.Thinking the mute had something to do with it,I left the sound on with the one speaker I had hooked up,but it still turned off whenever it felt like it.Usually around a minute,or two.For awhile I could turn it off,and back on when it tuened off by itself,but it got to the point where I would have to unplug it,and plug it back in to get the standby light to light red so I could turn it on again.
As far as the standby light goes,that is the way it is setup.When you plug the cord in,you have a red standby light.When you turn the TV on,the standby light turns off,and the TV turns on.
I would say that it might be overheating?Either that,or the coils need to be resoldered again,because they are heating up,and separating.Does the metal cage around the inverter act as a heatsink?All this time I have had it off.I also took the paste off the heatsink plates when I first started having trouble,so they are metal to metal.Before that,I had Arctic Silver on them when it started turing off by itself.Thank You very much!
Tyler

jts1957
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Aug 7, 2010, 5:46 PM

Post #9 of 17 (6616 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

MUST have ground. See if mounting screws secures ground foil trace on board when tightened. Otherwise if you're sure someone cut them, reconnect.

Metal cage = shielding
Thermal grease = for heat transfer. If it started out having it - leave it alone or add some (apply sparingly) if you think it needs it. Do NOT remove all from plates.

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(This post was edited by jts1957 on Sep 5, 2010, 4:30 PM)

70JUDGE
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Sep 5, 2010, 5:59 AM

Post #10 of 17 (6540 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Is the metal shielding to keep you from touching the inverter,or does it keep the interference out/in?
As of right now all of the paste is off frome the top of the heatsinks,and the plates that screw on top of them.The TV doesn't stay on long enough for them to get hot.
The TV only stays on for a minute,or so before it turns off by itself.Sometimes I have to unplug,and plug it back in to get the standby light to come back on.Sometimes if I hit the power button quick enough,the standby light will come back on without unplugging the TV.
I was told that I needed to use capacitors with low ERS,and not general purpose ones.Would that cause my TV to act the way it does?Right now I have the following brands,and series capacitors in the power supply.Rubycon MCZ,Rubycon YXA,Panasonic ED,Hitano EHR,Jamicon TR.
I measured the voltage on the wire that turns the backlights on,and I get 4.79 VDC when the backlights are on,and none when the TV turns off by itself.Does this mean that the backlights,and inverter are alright,and it is either the mainboard,or power supply turning the TV off?If I still had voltage on the wire when the TV turned off by itself that would mean either the inverter,or a bulb is bad?What is designed to turn what off,and for what reason?
What would I need for an inverter to test the individual bulbs?My TV has U shaped bulbs.I tried to use another monitor,but I guess it wasn't powerful enough as it would turn on for a few seconds,then off again like the TV sometimes does.Will one of the inverters for the neon computer lights work?I have seen some 12,and 24 volt ones.
There were two ground wires that went from the mainboard where the backlight on,and brightness wires are to the inverter that someone cut off.It got me thinking why they were cut off,but then it also go me thinking why they were there to begin with.The inverter is touching the frame of the TV in several spots,as well as being screwed to metal mounts.I also noticed a buzzing noise coming from the power supply.Thank You very much!
Tyler

jts1957
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Sep 5, 2010, 4:47 PM

Post #11 of 17 (6533 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Is the metal shielding to keep you from touching the inverter,or does it keep the interference out/in? All you mentioned.
As of right now all of the paste is off frome the top of the heatsinks,and the plates that screw on top of them.The TV doesn't stay on long enough for them to get hot. Wouldn't run it long time - if get set fixed add more.
The TV only stays on for a minute,or so before it turns off by itself.Sometimes I have to unplug,and plug it back in to get the standby light to come back on.Sometimes if I hit the power button quick enough,the standby light will come back on without unplugging the TV.Again sounds like it's locking up.
I was told that I needed to use capacitors with low ERS,and not general purpose ones.Would that cause my TV to act the way it does?Right now I have the following brands,and series capacitors in the power supply.Rubycon MCZ,Rubycon YXA,Panasonic ED,Hitano EHR,Jamicon TR.If manufacturer believed those were good enough to make unit last through the warranty??? Plus why would they put in best caps? They are trying to make a profit.
I measured the voltage on the wire that turns the backlights on,and I get 4.79 VDC when the backlights are on,and none when the TV turns off by itself.Does this mean that the backlights,and inverter are alright,and it is either the mainboard,or power supply turning the TV off?If I still had voltage on the wire when the TV turned off by itself that would mean either the inverter,or a bulb is bad?What is designed to turn what off,and for what reason? Do you have a variable power supply? Or three "AA," "C" or "D" batteries in series.
What would I need for an inverter to test the individual bulbs?My TV has U shaped bulbs.I tried to use another monitor,but I guess it wasn't powerful enough as it would turn on for a few seconds,then off again like the TV sometimes does.Will one of the inverters for the neon computer lights work?I have seen some 12,and 24 volt ones.
There were two ground wires that went from the mainboard where the backlight on,and brightness wires are to the inverter that someone cut off.It got me thinking why they were cut off,but then it also go me thinking why they were there to begin with.The inverter is touching the frame of the TV in several spots,as well as being screwed to metal mounts.I also noticed a buzzing noise coming from the power supply.Thank You very much!
Tyler

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70JUDGE
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Sep 6, 2010, 2:03 AM

Post #12 of 17 (6524 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Right now,the metal shield/cage is off from the TV.Could that be causing interference,and turning the TV off?
As far as the capacitors,the TV had low ESR KT brand to start with that went bad,so I replaced them with the following brands,and series.Rubycon MCZ,Rubycon YXA,Panasonic ED,Hitano EHR,Jamicon TR.What I wanted to know was if these were low ESR capacitors,and if I really needed low ESR capacitors for the power supply to work right/at all,or just to make it last longer?
What would be causing the lockups on the mainboard?General purpose capacitors in the power supply instead of low ESR ones?I did go from 10V 1000UF to 16V 1000UF on some of them.
What would supplying the 4.79VDC to the backlight signal wire do besides turn the backlights on?Unhook the wire from the mainboard first so it is not getting power from both the mainboard,and batteries?Isn't this voltage supose to be the same?Awhile back I thought I was getting around seven volts,now it is around five.
I also noticed a buzzing noise coming from the power supply.
What would I need for an inverter to test the individual bulbs?My TV has U shaped bulbs.I tried to use another monitor,but I guess it wasn't powerful enough as it would turn on for a few seconds,then off again like the TV sometimes does.Will one of the inverters for the neon computer lights work?I have seen some 12,and 24 volt ones.
There were two ground wires that went from the mainboard where the backlight on,and brightness wires are to the inverter that someone cut off.It got me thinking why they were cut off,but then it also go me thinking why they were there to begin with.The inverter is touching the frame of the TV in several spots,as well as being screwed to metal mounts.Thank You very much!
Tyler

jts1957
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Sep 6, 2010, 2:51 AM

Post #13 of 17 (6521 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Right now,the metal shield/cage is off from the TV.Could that be causing interference,and turning the TV off? Doubt it.
As far as the capacitors,the TV had low ESR KT brand to start with that went bad,so I replaced them with the following brands,and series.Rubycon MCZ,Rubycon YXA,Panasonic ED,Hitano EHR,Jamicon TR.What I wanted to know was if these were low ESR capacitors,and if I really needed low ESR capacitors for the power supply to work right/at all,or just to make it last longer? http://www.badcaps.net/forum/ for all your capacitor questions.
What would be causing the lockups on the mainboard?General purpose capacitors in the power supply instead of low ESR ones?I did go from 10V 1000UF to 16V 1000UF on some of them. ?; Doubt it; OK to increase working voltage.
What would supplying the 4.79VDC to the backlight signal wire do besides turn the backlights on?Unhook the wire from the mainboard first so it is not getting power from both the mainboard,and batteries?Isn't this voltage supose to be the same?Awhile back I thought I was getting around seven volts,now it is around five. If backlites stay on as long as you supply voltage, Inverter is likely good and bulbs are definitely O.K. You can disconnect wire from mainboard if you wish, but they usually don't when they jumper automobiles.
I also noticed a buzzing noise coming from the power supply. ?
What would I need for an inverter to test the individual bulbs?My TV has U shaped bulbs.I tried to use another monitor,but I guess it wasn't powerful enough as it would turn on for a few seconds,then off again like the TV sometimes does.Will one of the inverters for the neon computer lights work?I have seen some 12,and 24 volt ones. idk
There were two ground wires that went from the mainboard where the backlight on,and brightness wires are to the inverter that someone cut off.It got me thinking why they were cut off,but then it also go me thinking why they were there to begin with.The inverter is touching the frame of the TV in several spots,as well as being screwed to metal mounts.Thank You very much! Backlite on is need for enabling the backlite to turn on and backlite brightness will allow the backlite brightness to be varied. They would NOT go to ground.
Tyler

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70JUDGE
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Sep 6, 2010, 3:19 AM

Post #14 of 17 (6517 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

I also noticed that when the TV is on the tuner mode without the cable TV hooked up,the snow on the screen sometimes flickers.It also happens on the AV mode,but not as often.
What about increasing the capacitance?Can you go too high?What would happen?
The TV has a connector that had four wires in it.One is the backlight signal wire,one is the brightness wire,and the two missing wires,which were ground wires that went to the inverter.Why would you need the ground wires?The inverter is already grounded to the frame of the TV.
If I put the the battery voltage on the signal wire when the TV is on,wouldnt that double the voltage?If I put the voltage on the signal wire when the TV turns off,how will the lights turn on?Thank You very much!
Tyler

jts1957
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Sep 6, 2010, 3:27 AM

Post #15 of 17 (6516 views)
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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Think jumpering a car. It doesn't double the voltage there, by the time I explain you could have already performed the test. Angelic

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70JUDGE
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Sep 6, 2010, 4:20 AM

Post #16 of 17 (6513 views)
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Re: [jts1957] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Wouldn't the fact that the voltage on the signal wire for the backlights goes away when the TV turns off by itself rule out the inverter,and backlights?If you have a bad backlight,the inverter turns off,and you still have sound?If the inverter is bad,the same thing?When mine turns off,I don't have a picture,or sound.Thank You very much!
Tyler

jts1957
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Sep 6, 2010, 5:00 AM

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Re: [70JUDGE] Trutech PLV16260 LCD TV Turns On For A Few Seconds Then Turns Off [In reply to]	Can't Post

Normal: b-plus present and BLON= HI ... Backlites light and STAY lit. Remove BLON and backlites extinguish. Go into menu and raise and lower brightness and INT/BRI follows your raising and lowering.

Broken bulb (or shorted turns in Inverter transformer): b-plus present and BLON= HI ... Backlites light for a second and then go off.

Shorted inverter MOSFET device takes out a surface mount fuse on the inverter board: b-plus present and BLON= HI ... If you are in a darkened area you may discern a very quick, dim flash, otherwise lamps stay off.

ALL OF THE ABOVE, IF TUNED TO A VALID SIGNAL, DO GIVE YOU NORMAL AUDIO.

Quote

When mine turns off,I don't have a picture,or sound.

This is why I don't believe you have a backlite/inverter board problem.
Of course, they could now be designing sets so that if they don't have picture they kill the audio?

Going back aways, did you ever account for why the MBR4045PT was constantly beeping on your meter?

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(This post was edited by jts1957 on Sep 6, 2010, 5:09 AM)

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