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Why did my question disappear?

I ask a question last night and it disappeared, no trace. my question was: RCA 46, I have no backlight, but all LEDs work with LED tester? Why would I post other questions?????

Posted by George L Pate on

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2 Answers

Larry

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  • RCA Master
  • 3,308 Answers

Your question is here now. When you say your backlights all work how are you testing them?..Did you remove the panel to get at the individual strips or are you testing each string with a backlight testee at the power board and getting the same voltage on each string or can see them light up through the back of the set?

Posted on Sep 18, 2021

  • 12 more comments 
  • George L Pate
    George L Pate Sep 18, 2021

    I test at the connector where I disconnected it from the power board. i did open the back and verify all LED are illuminating, but I didn't actually test the individual LED strips.

  • Larry Sep 19, 2021

    I have a feeling some of the individual lamps are shorted and raising the current draw causing the safety section of the power supply for the backlights to shut down. You will see them light connecting a backlight tester to the connector at the power board, I'd pull the panel out and test each strip, if you have over 3 not lighting that would explain why they don't work. It's not impossible to have a power board issue but on sets with the issue you have about 95% of the time it's the LED bulbs that are causing it not to light.

  • George L Pate
    George L Pate Sep 20, 2021

    I have 10 strips with 8 LED each. Each LED draws 3 volts from the tester. Each strip draws 22.1 to 22.5 volts from the tester. All LED illuminate. The info on the strip says led should be 3.4 to 3.6 volt. P/N 3528A. Could all led be failing? TV manufactured in 2014.
    Something weird has happened. When I turn on the TV, the LED will illuminate until I turn the TV off. When I turn it back on the LED will flash and go off. After I unplug for an hour or so the LED will work again.
    I repaired my original power board (damaged solder pad from transistor removal) and I'm using it now. I did get two other used power boards but neither made the LED work, only a quick flash and back off, so I returned them. Attached pic shows all led illuminated from TV power board. I'm timing them to see how long they stay on. I assume if they stay on for an hour they will stay on until I turn the TV off.



  • George L Pate
    George L Pate Sep 20, 2021

    I just had another thought, could a failing capacitor cause these symptoms? I'm guessing capacitor ES4 and ES5 are part of the protection ckt, maybe, yes? See bottom right corner of power supply board.

  • George L Pate
    George L Pate Sep 20, 2021

    I kept the TV on for 2 hours, LED didn't go off until I turned the TV off. Only a short flash when I turned it back on.

  • George L Pate
    George L Pate Sep 20, 2021

    Power supply closeup. This is identical to my power board except on mine the two transistors are vertical instead of horizontal.

  • Larry Sep 20, 2021

    Considering all the buttons light and about the same voltage is seen on each strip (on your tester) it appears you do not have a strip issue. First thing to check is voltage of the 2 plus wires going to the strips, ground is to frame ground (after it's been running and the lamps go out). Test both circuits. What were looking for is do we have an issue with the feed or regulator section of the LED driver supply.

  • George L Pate
    George L Pate Sep 21, 2021

    Here are some voltage readings I got before I touched a pin on the optical isolator and shut the TV down. Waiting to restart after a while.

  • Larry Sep 21, 2021

    Refresh my memory...you had replaced the power supply and it didn't correct the issue..correct?
    I'm having trouble seeing some of the voltage readings, from frame ground to the black wire and blue wire on the connector going to the LED's in the panel did you get on the black wire 1.05 and blue 1.06 vdc? And on the 2 red wires did you get 132 vdc. Were these readings with the set on but backlights not working?

  • George L Pate
    George L Pate Sep 21, 2021

    Yes, tried two other used power boards. The LED didn't work with either of them, at all. I got a quick flash after the set is turned on, then nothing. Also no power to the LED connector, or anything in the general area. Backlights were working until i touched the pin on the optical isolator, then the TV shut down, and the standby LED didn't light up. If I let it sit unplugged for a while, the LED will work until I turn it off, that's how I got these voltage readings. After I touched the pin, power was lost on the top isolator output and the LED power was gone, Nothing from the two big diodes to the LED connector.
    The readings you stated are correct . Maybe you can see this better.

  • Larry Sep 22, 2021

    I really don't know what to tell you, you've replaced the power supply and it didn't fix anything, the LED's worked tell the set was shut off then only a flash, only other thing i can think of is a connection issue with the back light strips but it's seldom that happens. You can try contacting Funai (parent company of RCA) with the model and serial and they may be able to give you more advice but generally manufactures aren't any help diagnosing issues.

  • George L Pate
    George L Pate Sep 22, 2021

    Could you give me a part number for the optical isolator. I'm trying to look up a datasheet but not finding anything.
    Pn EL817B409 & EL817B403.

  • Larry Sep 22, 2021

    The generic one I use is PC817, I've never had a set it wouldn't work in. I'm not sure how hooking a multi meter to one of the leads with it on ohms would hurt anything, it would be like putting a 10 meg resistor to ground. What voltages are you getting across pins 1 and 2 , needs to be .75 to 1 volt to light the diode, if your not seeing that check the power on pin coming from the main. Problem is even if you get the set to power on again you still have the back light issue

  • George L Pate
    George L Pate Sep 27, 2021

    I have found the issue with my TV and was able to get it working. As I said, all of my LEDs passed every test I performed, but there was actually an issue with one LED that was preventing the LEDs from working. It worked intermittently with TV power but always worked with the LED tester. I was testing each LED with diode setting on my multimeter, and found one that was open until I pressed on it a little. I tried to resolder it but couldn't, so I just ran a jumper across it and everything is fine now.

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  • RCA Master
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The website is heavily dependent on scripts and are often glitchy. Often posters will post and not complete. We only delete Duplicate comments, inappropriate comments and spam posts. Sorry about that, it happens.

https://www.fixya.com/users/george-l-pate

Here is some information, but post again. We now have a television expert called Larry.

https://www.google.com/search?q=RCA+46%2C+I+have+no+backlight

..

Posted on Sep 17, 2021

  • George L Pate
    George L Pate Sep 18, 2021

    I posted the question again, and again it is deleted, poof, gone, disappeared.

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