Question about Vizio SV470XVT 47 in. LCD TV

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Vizio SV470XVT1A has no backlight. (If I shine a flashlight on the front of the TV I can see the picture, and I still have audio.) I have read the ''LCD Flat Panel TV trouble shooting guide'' and found that I do not have 24 volts to the two back lights inverter boards (there are two) from the power supply board. (Does this mean I need to replace the power supply board?) Is there anything that signals the power supply board to turn on the 24 volts to the inverter board--or is the 24 volts on all the time? Do the inverter boards turn themselves on and off when they receive the BL ON control signal from the logic board? I cannot see any bad capacitors, and I could only see one large fuse on the power supply board that is fine.

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  • ckmccollim Jul 30, 2010

    NOTE: When I wrote this, I had a few photos that did not post here. But you could look at Bud's site where he has a lot of photos posted about TV's ect. http://s807.photobucket.com/home/budm/al...
    =============================
    Hint: in taking the back of the TV off, lay it face down on a bed or on a carpeted/soft surface. When taking out the many screws in the back of the set?note that there four different kinds of screws. I made notes on paper as to the different screws locations, so I would be sure to get them back into the correct locations. With the help of another person, lift the bottom of the back up first?hinging it at a 45 angle on its top edge and then carefully ?pop? it off (I applied upward pressure.) There are snap in tabs of sorts on that top edge?so be care not to break those.

    budmrtn on www.fixya.com helped me trouble shoot this TV and fix it. Without his help, I probably would not have fixed this TV on the first try. I will summarize what we did to locate the problem.
    http://www.fixya.com/support/r5093881-lc...

    *** As stated above, everything on the TV worked, except the back lighting. I took the back of the TV off and all the capacitors (on all the boards) and fuses looked good.


    Note that there are many voltage labels on these power supply outputs. When the TV in plugged in (and turned OFF), you should have only 5 volts on the 3 pins labeled 5VSB (5 volt StandBy). This voltage should always there when the TV is plugged in. This standby voltage powers the logic board and the inferred receiver in the front of the TV, and the TV is watching for you to either press the Power On button on the side of the TV or to press the Power On button on the remote control. When the logic board sees this Power On command, it sends 3.3 volts to the PSON (Power Supply On) pin on the power supply board and a relay closes on the power supply board (you will hear a click noise) and the rest of the power supply voltages should be seen as they are marked on the board. (I had correct voltages on all the labeled pins with the exception of the 10 pins marked 24VI (24 volt Inverter.) When I unplugged the top Master Inverter backlight board connector (CN2, farthest to the top left in the photo above) I then had 24 volts at all these pins (always make sure you turn the TV off first, before you unplug wire connectors, etc.)

    I wanted to test the power supply to see if it could produce 24 volts under a load. I first hooked up two #3156 auto backup 27watt light bulbs (get them at any auto parts store) in series (daisy chain) with jumper wires and the power supply lit them up just fine. I also had two #H1 55watt Miata Fog Lights that I hooked up the same way to test an even greater load, and again the power supply powered these up fine with no problems.



    Now I knew the power supply board was probably fine, and I needed to trouble shoot the Master Inverter board. I unsoldered one leg of each of the two large capacitors, and tested each for being shorted or open (they tested fine.) I then tested the four Fairchild # FDB8447L MOSFETs,
    http://www.mouser.com/ProductDetail/Fair...

    and the top two in the photo below had a dead short between the back tab and the right leg (with the tab up).

    I decided to order a new Master Inverter board from www.shopjimmy.com
    http://www.shopjimmy.com/back-light-inve...

    They have an ?A? rating with the Better Business Bureau, and where great folks to deal with. Special note: make sure you call on the phone the parts supplier you are thinking about purchasing your parts from, and make sure the part is IN STOCK! I found on other popular sites that they say their stock will take ?4 -6 business days? (that means it is not in stock?it means they hope to get it from their supplier in 4-6 days and then will ship it on to you.) Pick up the phone and call to make sure it is in their possession and ready to ship.



    I put the new board in, and the TV fired up! We have been using the TV for two weeks now, and it works perfect.

    I believe I am going to order the Fairchild # FDB8447L MOSFETs and try to repair the bad board so that I have a spare. If the slave inverter board goes out, I will know how to test it, and will also know how to solder the parts in.

    Bud says this is how he gets the surface mounted MOSFETs off the board, ?The way I remove those surface mounted transistor is to cut the legs off then the legs can easily be removed from the board, to remove the transistor body, you will have to use at least 40watts soldering iron, you will heat up the tab of the transistor and also add more solder to it at the same time, the added solder will keep it hot, then while the soldering tip is still making contact with the tab you use a long nose pliers to twist the body of the transistor off the board, I have done may, it is easy if you have good soldering iron, just take our time.?

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The 24vdc is turn on by the signal from the main logic board, it is not always on, the standby 5vdc is always on. So yes it can be the power supply board is bad, but just to besure we need to find out if it is getting the turn on signal from the main board first.
You can have 24vdc at the inverter board and it will not light up the CCFL until it gets the signal from the main logic board to turn the lamps on (this is the STANDBY condition, the TV is on but the screen in not lit up util it see the video signal).
Send me good clean and clear pictures of the power supply board, budmrtn@aol.com, connectors of the Power supply, bottom side of the board, then I may be able to tell you which pin is a control input pin. Most people will just throwing parts in and hope that they one of the parts will fix the problem. Used Power supply module for this TV is over $100. http://www.google.com/products?rlz=1T4GGIH_enUS282US283&q=delta+DPS-379AP&um=1&ie=UTF-8&ei=USsxTKn3J6TonQfFlJGEBA&sa=X&oi=product_result_group&ct=title&resnum=4&ved=0CCsQrQQwAw

http://www.shopjimmy.com/catalogsearch/result/?q=Vizio+SV470XVT+

Posted on Jul 05, 2010

Testimonial: "Bud helped me fix my TV! It was only 1 1/2 years old. I was looking at a repair bill close to $300 - $500 and I fixed it with a $60 board! Thanks!!!"

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