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ricke1973
ricke1973, ELECTRONICS
Category: Consumer Electronics
Satisfied Customers: 7429
Experience:  DEGREE IN ELECTRONIC TECHNOLOGY
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Have Sylvania 42" 1 yr old lcd tv. LC427SSX. No pic at all,

Resolved Question:

Have Sylvania 42" 1 yr old lcd tv. LC427SSX. No pic at all, all else ok. No pic on other inputs either, problem is internal. Worked fine one evening, no pic the next morning. Tv powers up ok, speakers work fine. Tried flashlight shining on front of tv, no image. Have 24.5vdc on all red power supply board feeding backlight inverter pannel. The 2 main fuses on that pannel are good too. Is this inverter board most likely problem. Called sylvania, they won't help since a few days out of warranty. Just trying to Isolate problem before I buy a board on eBay.
Submitted: 3 years ago.
Category: Consumer Electronics
Expert:  ricke1973 replied 3 years ago.

Hello my name is Rick

 

First let me say sorry I don't have a quick fix for this problem.

The problem you are describing is a very common one in LCD sets like yours. The TRANSFORMERS MAY BE BAD ON THE INVERTER BOARDS,, OHM THEM OUT AT THE PIN CONNECTOR THAT GOES TO THE PANEL,, MAKE SURE THEY ALL READ THE SAME,IF NOT YES YOUR INVERTER IS BAD

 

 

If you would like any additional information or have more questions please don't hesitate to ask!

Customer: replied 3 years ago.
Are you referring to the outputs of the high voltage transformers? If so, all ohm readings are the same. I also get same readings on the primary inputs of these coils. I have noticed that on one of the power harnesses coming from the main power supply board, all red are 24.5vdc and the volt readings on the 4 blue wires are 2.8, 2.2vdc, and the inner 2 blue wires are 0vdc.

So if I read this reading on the high voltage output transformers correctly, then am I correct in assuming the problem is elsewhere?, Thanks.
Expert:  ricke1973 replied 3 years ago.
Ok check on the main board you should have a active low,, and this low causes the power supply to click,, if you here no click then i will say its the main board,, but if you here the click the problem has to be the inverter
Customer: replied 3 years ago.
Thanks again, The blue relay does click when powered up. Voltage on the top red output leads goes from 4.7 to 23.5. There are 3 heavy leads going out the side of the power supply board to the jack power board also. white one reads -30.5vdc, black one reads -54.5vdc and no reading on the red one. (Neg meter lead to chassis ground.   Oddly, the wife said occasionally when she is sitting in the living room with the tv off, she will hear it click, on its own, like the turn on click of the relay. It still stayed off though. Output at the main rectifyer is 54.5vdc and -54.5vdc.
Customer: replied 3 years ago.
Thanks for your previous answer, if there is any other tips to help isolate the problem, they would be appreciated, I am ready to accept your answer then.
Expert:  ricke1973 replied 3 years ago.

(Please click on high lighted words) If too technical cost for repair is around

Friend this is a very common problem with plasma LCD and also DLP within the power supply the capacitors also click here Start to fail and the way you can tell is to check them visually for swelling or expanding of the top. ALSO click here ,, and here also,,

It will be easy to see the bad caps will not be as flat on the top as the good ones, But also you can have a bad resistor or diode and even a bad regulator. Would like for you to take your meter and place it on DC voltage the positive end on every connector that says a voltage and the negative wire to the panel this is the best ground. Turn on and see if the unit tries to climb. If you don't find one that's trying to climb, another method is to locate a short circuit. Place meter on ohms or beep test follow same procedure no voltage should be shorted to ground. And this is the problem,

Exchange them and you will be ok, Well good luck friend. And if it doesn't work make sure the power supply is sending 24v to the inverters when you turn the set on your meter should climb but won't reach 24v because unit will shut down and if so we ruled out the inverters or back light I seen this problem also caused by the signal board it has a power on command missing and it looks like the power supply is bad but actually it's the signal board, it may be labeled on the board a active high or low 5v which sends the command to the power supply.

Good luck friend, and if my efforts are appreciated, feedback and or bonus will be appreciated

Capacitor pictures inverter pictures... cold spray can be used if your set works for awhile then shuts down. If you click here this is a complete process for troubleshooting a LCD

Please let me know if you want to try this yourself, or if there is anything else I can do for you!

If you would like any additional information or have more questions please don't hesitate to ask!

ricke1973, ELECTRONICS
Satisfied Customers: 7429
Experience: DEGREE IN ELECTRONIC TECHNOLOGY
ricke1973 and 5 other Consumer Electronics Specialists are ready to help you
Customer: replied 3 years ago.
Extremely helpful

A+++
Expert:  ricke1973 replied 3 years ago.
thank you
Customer: replied 3 years ago.
Rick, thanks for your help, I found the problem. There are 3 fuses on the backlight board not 2 like I saw. The smallest of them all, a 1/8" long black cb fuse, was blown. Caps all look good on that board, and no other visual problems along with the good ohm readings on the output transformers secondary windings. I temp soldered in a 1a, inline fuse and yes it worked. Original was a .75a fuse. I looked through all my junk circuit boards and did not find any.
Expert:  ricke1973 replied 3 years ago.
Great job Sir
Customer: replied 3 years ago.
Thanks again Rick, Tv is still working good.
Expert:  ricke1973 replied 3 years ago.
ok

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