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Shahid
Shahid, Technician
Category: TV
Satisfied Customers: 10079
Experience:  I have been repairing electronic gear since 1993 as a qualified Sony tech
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Cant tell if this tv is led or ccfl...have both testers, but

Customer Question

Cant tell if this tv is led or ccfl...have both testers, but not sure which to use. Comes on flickering, then light goes out. Can still see video and hear noise
Submitted: 2 months ago.
Category: TV
Expert:  Shahid replied 2 months ago.

Hi, my name is ***** ***** I will do my best to help you today. To make sure I don’t miss anything, please give me a minute to review your question.

Expert:  Shahid replied 2 months ago.

Can you please get me the model number of the TV?

Customer: replied 2 months ago.

42 pee eff el (phonetic spelling of letters) 6704d / eff 7

Expert:  Shahid replied 2 months ago.

42PFL6704D/F7

This TV has CCFLs.

Its power supply board has inverter section for backlight system.

Customer: replied 2 months ago.

I figured. I just didnt want this ? To get lkd, thats why im being cryptic lol. So i tried software upgrade...was successful, but no change. Lights up briefly then goes dark. What should i chk....outgoing voltage from pwr supply?

Customer: replied 2 months ago.

There are two outputs....two wires each, vut 3 pins each. Do i test for DC voltage?

Expert:  Shahid replied 2 months ago.

Correct, the inverter section on power supply board seems have got problem, I don't have detailed schematics of this board so I may not help to repair it on component level. CN2 and CN3 should have approx 600V AC output that goes to CCFLs.

Customer: replied 2 months ago.

Which pins do i test? Its got 3 pins, but only two wires. Middle seems to be empty on the plug, other two are white and pink. Im guessing white is groind, pink is lead?

Expert:  Shahid replied 2 months ago.

I guess whole connector is one pin, I mean all three pins are just one if you check underneath PCB lines.

I'm saying this because that much AC volts having high frequency usually jumps to nearby pin/ part that is why they made two connectors on safe distance to avoid any arc. If you remove power board and check the PCB line on other side of board you might see all 3 pins of connector soldered on one PCB line.

If that's the case then need to check AC volts across the both connectors only, no ground of TV chassis will be used.

Customer: replied 2 months ago.

Without taking the board off to look at the tracers, just looking underneath, the pink pin is soldered to the center one, and the white is by itself independent

Expert:  Shahid replied 2 months ago.

This is odd as the circuit board design doesn't fit with the pins layout. Can you take picture of PCB side of board please?

Customer: replied 2 months ago.

Sure thing. Give me a few minutes....im going to take some readings from those big harnesses, then take the board off. Would be a good time to test capacitors anyway. And it may just LOOK the way i described from the side, PCB side of board may show us different. Going to post you another question before any of that, in about 2 minutes

Expert:  Shahid replied 2 months ago.

OK, no problem, take your time.

Customer: replied 2 months ago.

The new question is posted to ya, i will take a picture soon as you pick it up. And i will get on taking off that power board. I am watching one football game in the room im working, and listening to another game in the other room, lol, so im working as fast as i can

Expert:  Shahid replied 2 months ago.

hah, enjoy your work!

Expert:  Shahid replied 2 months ago.

Ed, is that LG 47LG50 TV question?

If so, you have posted it in wrong category and I'm unable to access it.

Customer: replied 2 months ago.

Boooooo, I asked him to close the question. Let me post it in the right category

Customer: replied 2 months ago.

I posted it directly yo you again. Thats what i did the first time, asked it from YOUR profile...looks like they might be screwin with us again....u still have my contact info in case my act gets lkd up? Being new years day, I doubt theyd release it very quickly. And I have lots more work to do today and tonorrow, preferrably with you specifically

Expert:  Shahid replied 2 months ago.

Category select drop down list is bit sensitive issue and I can't pick the question for those categories that I'm not allowed.

Customer: replied 2 months ago.

No worries, we got it now. So this board is off, and yes....all one circuit for all 3 pins.

Expert:  Shahid replied 2 months ago.

Wow OK, thanks for the picture. You would need to check high frequency AC volts across both connectors.

Customer: replied 2 months ago.

I sure will, but not yet. Found a 50v 22uF cap that i THINK is bad, the solder points are so damn close im not sure, but seems like its bad, tested 3 times good if less than 22uF, whereas the replacement cap reads good if less than 1000uF, obviously diff readings. So imma replace that and check the rest and replace whats necessary. Ok, so I need to run out for about an hour and a half and pick up 2 more tvs, so in the meantime, let me start 3 fresh questions, so you can be working on stuff while im out. Look for them, im going to post them right now and make sure you get them before I leave to grab these other 2 tvs

Expert:  Shahid replied 2 months ago.

OK, I'm ready.

Customer: replied 2 months ago.

OK, so I replaced the one capacitor on the power supply....all the rest tested good. Still having the same behavior. Looks to be one mosfet bad on one of the rail lookin things...i THINK its a bridge rectifier? Not sure. But the mosfet has the numbers and letters darkened a little in the middle...i only noticed because theres an identical one right next to it and the numbers and letters are clearly visible, no darkening. But I certainly need direction on what I'm lookin at and how to test it. And as far as testing ac current. Am i testing both connectors on cn3 seperate from both connectors on cn2? Or all 4 pins at once?

Customer: replied 2 months ago.

I got some readings from the power supply outputting to the ccfl's.....so i tried measuring both pins on CN2 at the same time, and it shut down the TV. Same thing with testing both pins on CN3. when i tested each pin individually, got the same results for all: when i powered the unit on, the volts AC read 400 then up to 900 the up to 1300-1400, then down to 700-800, down to 300-400, back up to 600, then steadily down. Is that normal? Maybe a voltage regulator? Mosfet? Im lost on that, need to know what and how to test. Regardless, though, when I tried applying my ccfl tester to 2 pins at once, no light. All 4 pins at once, no light. Should i try just one pin at a time? Maybe my tester doesnt supply enough voltage? My ccfls are shot? Help please, this one has me stumped...im moving on to the next one.

Expert:  Shahid replied 2 months ago.

Are you testing volts on power supply board connectors *CN2 and CN3)?

On what terminals you're connecting CCFL tester?

Customer: replied 2 months ago.

Yes, those are the ones i tested. And inam connecting the ccfl supply to the wires that i disconnected from those cn2 and cn3 connectors

Expert:  Shahid replied 2 months ago.

OK, it seems inverter section works so you get AC volts 400 to 1400 reading between CN2 & CN3, all the pins in CN2 are same so consider it one pin, same thing for CN3

If CCFL tester doesn't lit the CCFLs when connect both connectors (one connector consist of white-pink wires) that means there is some thing wrong with CCFLs

Customer: replied 1 month ago.

Gonna get ya next step on this one later tonight when i get home...but if the ccfls ARE bad...doesnt seem to be any specific ones for te0lacememt...is it just ones from same size TV? Seems like they all connect the same. And i want to test a CCFL that I KNOW was good when I took it out to make sure my ccfl tester is functi9ning correctly...so on a CCFL tube, is one end positive and one negative? Or both positive, or...what? Seems like most tubes, theres an end that looks like vulb all the way to the tip, and one end that has like a little silver collar right before the tip

Expert:  Shahid replied 1 month ago.

CCFL lights up on AC volts so it doesn't have any polarity. It is like florescent tube light used in home for light.

Customer: replied 1 month ago.

So i apply power to both ends at same time? And like i said in other questions, im pretty sure my ccfl tester is broken, so what voltage should i set my benchtop power supply to? And its got 2 settings...one with amps, one without...im guessing one is AV and one is DC....ive sent you pics on other questions, but this is the power supply...it maxes out at 35 volts per side (pair), and theres a left section for 35v max and a right section for 35 volts max. There's a pushbutt9n selector, has a dotted line and a solid line...when it's "on", theres no amps, when the button is pushed to "off", theres amps.

Expert:  Shahid replied 1 month ago.

Ed, that power supply provides DC volts and CCFL needs AC volts at least 200V to test it.

You can't use the benchtop power supply unit to test the CCFL.

Customer: replied 1 month ago.

Ah, gotcha. Boooooooo. Ok, ao im going to order another ccfl tester, but id ALSO like to buy a benchtop power supply that is capable of producing the required AC volts to test ccfls.....so i am looking for something that produces ac volts. And between 200 and 1400 volts? Im guessing crom what you said that 200v is the minimum...what is the maximum I should look for in a power supply?

Expert:  Shahid replied 1 month ago.

Ed, that AC volts are high frequency as well, that isn't 60Hz AC volts but very high frequency to give flicker free light from CCFL so a new tester would be fine. Handling AC power supply unit up to 600V would be risky and hazard.

Customer: replied 1 month ago.

Gotcha. So in the meantime....multimere leads one to each of the hot pins in those sockets, to read ...somwhwrew between 200v and 1500 v?

Expert:  Shahid replied 1 month ago.

Correct, such reading should appear.

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