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Guides and repair information for televisions from Hitachi, a Japanese electronics manufacturer.

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Need help with backlighting issue on my Hitachi TV

My the screen on my Hitachi tv (43hk25t74u) has recently stopped working. The audio is still there, just no picture. I have done the flashlight trick and can still see some images vaguely, so I'm assuming it is the backlight.

Now from my understanding, it's either a problem with the power supply, or the led strips have failed.

I have opened my tv and looked at all the components, but can't see any obvious visible issues. But I'm no expert, so I have attached some images in the hopes somebody more experienced can spot the issue.

I think I can rule out the power supply being broken by using a multi meter, so if anybody can point out any issues, or point out where I need to check the LED power supply with a multi meter, that would be greatly appreciated!

Then I can be sure it's the strips that need replacing and get them ordered.

Thanks,

Ross

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Ross P, I can’t see anything on the boards that concerns me much. Have you tried measuring the output voltage of the inverter board, that drives the backlight? Try measuring the output and let us know what the voltages are as that can help in diagnosing.

There are two main ways of testing the backlight:

  1. Test the output of the inverter board
  2. Apply the correct power to the backlight externally

2 requires a power supply that can provide the correct voltages at the appropriate amperage. Should light up the backlight if it’s working. There are some backlight tester thing-a-ma-jiggies / do-hickey’s on Amazon, though I’ve never used them myself.

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Thanks for your reply, much appreciated.

I'm not entirely sure where I need to measure the voltage. Is there any chance you can point out where the power gets sent to the backlights, as i've got no idea lol.

Thanks

par

Ross P, Sorry for taking so long to answer! I was out for an afternoon walk :)

Are you experienced with reading schematics, troubleshooting and measuring? Here is a link to your main board (Vestel 17MB130S) service manual. Page 43 shows the troubleshooting section on the backlight.

Start by measuring the LED connector (bottom left connector, see image on page 5). The output voltage should be fairly “high”, can be up to ~48V.

If the voltage is there, follow the checks, like measuring Q113 (it’s a SOT-23 package) here is the data sheet for that transistor. The collector (pin 3, the top “lonely” pin) should be high, when the backlight is on.

par

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