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**nomoresonys** · 01-16-2019, 08:27 AM

Re: TC-55CX400U Panasonic TV red light but black screen

Panasonic usually makes pretty good tvs, might be worth fixing.

**nomoresonys** · 01-16-2019, 08:28 AM

Re: TC-55CX400U Panasonic TV red light but black screen

Test all pins on connector from mainboard to powerbard on powerboard side, all board connected. Test in standby/plugged in but off, then apply power report both conditions, example: pin 1 bl-on=0 volts standby and 3.3 powered on, report results for every pin.

**observer247** · 01-16-2019, 10:05 AM

Re: TC-55CX400U Panasonic TV red light but black screen

Thank you for responding. I am new to using multimeter. One question. Please check the attachment (to this comment). I am supposed to measure the voltage at A (marked with yellow), right ? But around the area where I marked with A, its little difficult as there is not much space (still can do). But what if I measure at the Main Board side after pulling out the tab, ie the area marked with B.

So this is what I will do, overall:

A) Have the TV plugged out
B) Plug in the TV. Do a round of measurement.
C) Press the power button on the TV and do one round of measurements.
D) Report here.

Attached Files

**budwich** · 01-16-2019, 01:26 PM

Re: TC-55CX400U Panasonic TV red light but black screen

in general, a "wire is a wire" meaning that if you can't get access to the wire at one end, go to the other and measure there. In this case measure at B. You just have to make sure that the wires from A are in the position at B... follow and make note of any changes to the pin numbers.

Further, make sure you report the actual label also as the picture is not necessarily readable. Further, check for similar "labelling" on the main card that provides other possible signals / voltages that need checking.

**observer247** · 01-16-2019, 07:37 PM

Re: TC-55CX400U Panasonic TV red light but black screen

I took all the readings. The table is attached. Some of the pins (towards the middle) are little hard to reach.

I tried to take out the tab (B) in the previous image. I know its a silly question but how to pull it out. Should I press the tab in any specific direction and pull. Then I can get more accurate readings from the Control Board side.

And please let me know if I need to do any more readings. I cross checked the results around 4 or 5 times. I also uploaded a clearer picture of the voltages printed on the board. Thanks once again.

Attached Files

**budwich** · 01-16-2019, 09:24 PM

Re: TC-55CX400U Panasonic TV red light but black screen

those readings appear to be fine / as expected. as for taking off the cable, not sure, probably pushing on the side tab and then lifting the connector.... but you don't need to remove the connector, you can use a pin to touch thru the upper portion of the connector to the pins.

Anyway, you can try disconnecting, one at time, the ribbon cable going from the tcon to the panel and see if that changes anything when powered up in terms of the display and main card.

Further, the tcon (bottom board) should see the 12v somewhere as it comes from the main (switched by the main from the power board) towards it. There is usually a fuse on the board which should be checked also.

**observer247** · 01-16-2019, 10:36 PM

Re: TC-55CX400U Panasonic TV red light but black screen

So this is what I understood. On the TCON board (the bottom board, marked in my attachment), I need to check for the fuse. Also somewhere it should show 12V.

When you said disconnect one at a time the ribbon cable, I see three ribbons. Should I disconnect one by one (keeping at most one ribbon disconnected at one time) ? Which part is called the panel ? I will check the display but what to check on the main card ? Thanks.

Attached Files

**budwich** · 01-16-2019, 11:33 PM

Re: TC-55CX400U Panasonic TV red light but black screen

those cables on the bottom go around and connect to edge board that are attached to the panel. Unclamp / disconnect one at a time (only one disconnected at any point in test). Check the resulting display for any signs.

As stated, there will be 12v somewhere on the tcon as that voltage comes from the main card to power the tcon and more.

As for the main, the voltages go from the power board to the main... you can trace visually or with a meter or possibly looking for labelling on the card.

**nomoresonys** · 01-17-2019, 12:30 AM

Re: TC-55CX400U Panasonic TV red light but black screen

Tcon fuse will start with F, looks like F104 or something close, it's white close to the left connector, check meter set at 20 vdc, black probe to a ground, touch red probe to each side of fuse, looking for about 12 volts on each side. Also unplug cable from powersupply board to mainboard as suggested then plug tv in turn it on see if backlights come on and stay on.

**observer247** · 01-17-2019, 08:09 PM

Re: TC-55CX400U Panasonic TV red light but black screen

One important update is that the sound works (connected laptop to hdmi) and trying various inputs took to the right input. To power on for some reason, have to press power for 10 seconds. The remote works when I mute the TV, volume up-down or change inputs.

Also a new update is I see a red light on the boards (attached photo)

As far as the next steps suggested, I tried the following:

Removed the ribbons on the tcon board one by one (the ribbons marked in the photo). I did not see any change in the display.

Please check the tcon board photo. I could not find the fuse on the tcon board. So could not check voltage.

Any suggestions on next steps ? Does the audio working and the red light on the board point to any specific direction. Thanks once again.

Attached Files

**budwich** · 01-17-2019, 08:21 PM

Re: TC-55CX400U Panasonic TV red light but black screen

sound indicates that the main board is processing the "complex" hdmii signal... which is good.

As far the fuse, you need more diligence.... you need to be able to look at the WHOLE board... note your pictures show bracketing. The fuse will likely be near where 12v comes into the board.

**observer247** · 01-17-2019, 09:08 PM

Re: TC-55CX400U Panasonic TV red light but black screen

I will check for the fuse on the tcon board. Do I additionally check under the black cover. Or do I have to remove the aluminium bar. I am assuming the fuse is on the top and not under the board. So next is I will look for the fuse.

Another thing I noticed now (with room dark) is that when I press the power button for 10 seconds, before the sound comes on, there is a light flicker on the left side of the screen for a fraction of a second. I could not see any panasonic logo etc on the screen though, just a light flicker before the red led turned on.

From what you have seen till now, can we rule out certain failures ? For example not a power board problem etc. Thanks

**observer247** · 01-17-2019, 09:29 PM

Re: TC-55CX400U Panasonic TV red light but black screen

This is the image of a t-con board. Can you please point where the fuse is ? https://www.wavesparts.com/wp-conten...22a50c7f50.jpg

**budm** · 01-17-2019, 09:43 PM

Re: TC-55CX400U Panasonic TV red light but black screen

White body fuse on the left of the left LVDS connector, rated at 32V 7A as printed right on the board.

**observer247** · 01-17-2019, 09:49 PM

Re: TC-55CX400U Panasonic TV red light but black screen

Found the fuse. Attached photo with arrow.

The photo is of my t-con board. Where do I check for 12V and what should be the voltage on the way out of the ribbons.

Attached Files

**observer247** · 01-17-2019, 10:04 PM

Re: TC-55CX400U Panasonic TV red light but black screen

Update: I checked the voltage on both sides of the fuse. Its 11.65V on both sides. Also I disconnected later the cable from power board to main board, I could not see any backlight.

I checked the fuse. It shows 000 which means its good. Which points do I check the powers at (for 12V) incoming and outgoing ? Should I check the pins near the LVDS connectors. Thanks.

**budwich** · 01-18-2019, 12:39 AM

Re: TC-55CX400U Panasonic TV red light but black screen

If you look at your tcon, there is a vcom point and vref. check those, especially vcom. There might be others labelled so look at those especially toward the panel cables.

Further, your "hold the power button for 10 sec"... potentially is a type of "force on" for panasonic... at least that is what is used in their plasma sets.... usually the system then may flash an error code there after but it appears that is not happening for this model... maybe.

Further, on the power board, there are other connectors / voltages going to the back lights and other places (can't read the labels. Check those, especially going to the back lights.

**angelos** · 01-18-2019, 01:02 AM

Re: TC-55CX400U Panasonic TV red light but black screen

Yes, check the voltages going to the backlights since you get a flicker or flash perhaps the LED driver circuit is shutting down due to an error on the LED's in the panel. There would normalyy be a large voltage. Sometimes in excess of 200V DC.

**observer247** · 01-18-2019, 10:11 AM

Re: TC-55CX400U Panasonic TV red light but black screen

@budwich when you say check " vcom point and vref". What do I check ?

I uploaded a high quality image of the power block. Once the image load, there will be a link saying "Load Full Resolution". Click on that please
https://ibb.co/MNb8SDn

If this is not clear enough, uploaded same in two parts:
https://ibb.co/qjDY89Z
https://ibb.co/34FmKMm

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TC-55CX400U Panasonic TV red light but black screen

TC-55CX400U Panasonic TV red light but black screen

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