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DP42D23 Has power & sound,no picture. I see screen with a flashlight.

Sanyo DP42D23, power and sound but no picture. Picture is visible with a flashlight. 120V is good. I’ve checked DC voltage at K702, There is 12V at the pins required. This is about as far was I’ve gotten with my limited ability. Any help is appreciated.

Ted

Update (11/15/2019)

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Hi @nict ,

Couldn't find a service manual for the TV but you're description indicates a problem with the LED backlighting.

Found this link which may help to get you further on to resolving the problem

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I followed your link, however, I'm not sure what a lot of these things are. Beyond my knowledge of LED TV's.

さんによる

Hi @nict

Try to keep things simple.

In the link above, in the 2nd last post it mentions that the problem was a bad cable connector between the power board and the LED array board.

You never know, you may have the same problem.

The LED array board is where the LED backlights in the screen are connected to.

Perhaps you could used an Ohmmeter (disconnect the power from the TV first) and test for continuity on the wires between the the power board and the LED array board.

Maybe even disconnect the cable at both ends and inspect the ends for corrosion or dry joints where the connector sockets are mounted on the board.

Can't see it too well from the picture you posted of the Power board, but where does the cable (4 wires 2 x black and 2 x white) go from the white connector shown at the bottom of the board in the picture?

Perhaps you could measure the voltage on them. To be safe as I don't know what they're for or where they go, start the Voltmeter on highest AC voltage and then scale down to get more accurate reading or change to DC Volts after you know that it is not high AC volts.

さんによる

Thanks for keeping it simple.

If the array board is the one with function buttons and HDMI connectors, there is a 14 wire harness that runs from it to the power board. I disconnected it, checked continuity on each wire and inspected the plugs. All are okay.

I've added two more pics at the top that might be better of the 4 wire plug. The wire go directly into the metal back covering the screen. The plug end is marked LED- on one end and LED+ at the other. The voltages are erratic. AC voltage is .3 - .4 on the black wires, and .1 - .3 on the white wires.

Ted

さんによる

Hi,

It says LED on the board it must be the feeds to the LED array board.

Measure the voltages on the connectors (should be near to what was mentioned below but to be safe use highest AC then DC voltage scale). Don't know for sure but maybe the white wires are the LED power supply and the black are the return path. You'll soon know which is which by measuring them

Trace the cable to the end and measure again.

If the voltage is OK and the same the problem will be in the LED array.

If the voltage at either end is low (assuming <68V but may be wrong about the value, on BOTH LED power leads) then there is a problem on the Power board

さんによる

Hi,

The array board will be in the metal back of the screen.

Did you unplug the LED connector cable from the power board and visually inspect it, both plug and socket?

What is the DC voltage on the LED terminals on the power board?

From what you said earlier and if @oldturkey03 is correct there is insufficient voltage on the BL_ON lead on pin 12 it should be nearer to 3.3 volts as per what you saw on pin 13.

Did you read these same voltages where they appear on the Power board as well?

Perhaps the power board needs both BL-ON voltages to be correct before turning on the LED power and not just one. I don't know. If it only needs the one BL-ON for each LED array (are there two only?) then why isn't one LED strip being turned on as you read 3.16V on pin 13

So we're a bit closer but not much.

It looks like it is the mainboard not sending the correct signal value to the power board on the BL-On pin 12

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@nict it always pays off to give all the voltages. Remember that this is a backlight issues so you need to get the voltages for BL-On (~3.3V)and BL_DM as well. Then measure the voltages on your backlight connectors. If all of those check out your TV is having issues with the backlight array. If the voltage do not check out, you are having trouble with your power board.

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Pin 1-3 68V Pin 5-7 100V

This is not an answer but just an augmentation to @jayeff answer

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I may been in over my head. Not sure what or where "BL-On and BL-DM are located. I can see the obvious power board. I don't know which is the array board. Also don't see anything that is on the above diagram "Symbol (CN201 or LBP)" so I've not checked those voltages. I'll post pics of my boards in the section below "Add to your answer".

Photos are added to original post.

さんによる

On the K702 plug, both pin 12 and 13 are labeled BL-On. pin 12 is 1.16V and pin 13 is 3.16V

さんによる

Ok so that is proper voltage for your BL On. Let me see if I can mark where to measure the voltages on the power board.

さんによる

On the four wire connector K701 check voltages at led1+ and led1- as well as led2+ led2- with power on. Then turn your TV's power off and unplug the connector. Do the same voltage check while you push the power button to turn your TV on. That will give us a maximum voltage when the TV gets turned on. Let us know what you find.

さんによる

Use this video from ShopJimmy as a guide on how to check it

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I don't know if you have fixed your tv yet, but my issue was a burned out led in one of the strips. I didn't have the led/backlight testing tool so I used this video to diagnose which strip was faulty. https://youtu.be/4pK6o2DMLWQ

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Ted Nicolai さん、ありがとうございました!
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