Panasonic TX-48CX400B - No Video

[tmcw]

Hi, looking at this TV set, I can hear the audio, LEDs/backlights are on, but there is no video, here are some details...

Panasonic TX-48CX400B

17IPS20 power board and 17MB100 mainboard.

With HDMI source, I can hear the audio fine, but I can't see any video.

But the LEDs seem to be on, I can see the light coming through the holes on the metal plate at the back, that the circuit boards are attached to, and I can see an even layer of light on the LCD panel at the front.

The TV was on this afternoon for a few hours, audio continued to play, while the LEDs stayed on. When the TV is left on without a video source for maybe 5 minutes, the backlight/LEDs switch off.

I've attached a photo of the back showing the light getting through the metal plate, I'm thinking I'm not having a problem with the LEDs, but elsewhere.

I have read other threads with similar/same power board, but those problems were saying that they could see images on the LCD panel with the aid of a torch; I don't think I'm getting video to the panel.

What should I test first? It might be worth a bit of time if the panel is ok.

Thanks.

[diif]

Re: Panasonic TX-48CX400B - No Video

Check the fuse on the tcon.

[CapLeaker]

Re: Panasonic TX-48CX400B - No Video

check all the different inputs as well.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Check the fuse on the tcon.

Yes, the fuse is ok, and I'm getting 11.83V either side of it.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

check all the different inputs as well.

Yes, I tried all HDMI inputs, and they give the same result, audio, but no video.

I will try the VGA, and component too, I think I have a media player that will output component.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Yes, I tried all HDMI inputs, and they give the same result, audio, but no video.

I will try the VGA, and component too, I think I have a media player that will output component.

Same results with VGA and component, no video.

[Trevtron]

Re: Panasonic TX-48CX400B - No Video

Do you get any graphics? I.e. menus, volume bar etc.?

[nomoresonys]

Re: Panasonic TX-48CX400B - No Video

Faulty tcon? try with power unplugged, remove one side of tcon ribbon connector, plug in tv, power it on, see what display you get if any then do the same for other ribbon connector.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

I came back to this set, and have seen the above new posts...

No graphics on screen whatsoever, no menus, volume bar, etc., but the buttons do work, as I can hear the sources switching, and the volume goes up and down when the appropriate buttons are pressed.

I also tried unplugging both sides of ribbon cables on the t-con board (one at a time) but it made no difference to the display, still no picture, graphics, etc., but the backlight is still coming on as reported before.

I had a look at the t-con board, and could see a couple of places where voltage is marked, I was getting 11.78V at the place marked 12V (on the U1 connector), and up from that in the middle of the board (as per the attached photo), I am getting 3.3V at the place marked 3.3V.

Are there any other tests I can make on this board?

[nomoresonys]

Re: Panasonic TX-48CX400B - No Video

Hmm, maybe throw a tcon at it, see if that's a match: https://www.ebay.ie/itm/PANASONIC-VE...8AAOSwDZ9bsfy6

[budm]

Re: Panasonic TX-48CX400B - No Video

There are many Voltage test points on that T-CON board: Test those Volatges with and without ribbon cables between LCD panel and the T-CON board.
HVIN_12V
VCC_3.3V
VCC_1.8V
VCC_1.2V
VCC_1.1V
VCLN.

I cannot see VGH, VGL, AVDD.
Does it have test points on the bottom side of the board?

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Thanks for that list, I'll test them out.

I don't think there are any on the other side, I'll upload an image of it, if you wouldn't mind double-checking for me.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Here are the voltages off the various test points, before and after panel ribbon cables connected...

VIN_12V ... 11.78 ... 11.82
HVIN_12V ... 0.06 ... 0.06
VCC_3.3V ... 3.32 ... 3.32
VCC_1.8V ... 1.80 ... 1.80
VCC_1.2V ... 0.94 ... 0.95
VCC_1.1V ... 1.15 ... 1.15
VCLN ... 0.10 ... 0.01

Is the VIN_12V of 11.78 / 11.82 good enough?

Also, is the drop on VCLN from 0.10 to 0.01 significant?

[nomoresonys]

Re: Panasonic TX-48CX400B - No Video

Looks like HVIN is way too low.

[diif]

Re: Panasonic TX-48CX400B - No Video

VIN_12V IS OK BUT you're missing HVIN_12, and the 1.2V looks off also.
AVDD is next to the left hand LVDS socket.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Thanks for pointing out AVDD, I don't know how long I've looked at this board and didn't see it!

AVDD is 0.01V with the ribbon cables connected and not connected.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Hmm, maybe throw a tcon at it, see if that's a match: https://www.ebay.ie/itm/PANASONIC-VE...8AAOSwDZ9bsfy6

Thanks, that looks like the same board, and is fairly cheap, might be worth a gamble?

[budm]

Re: Panasonic TX-48CX400B - No Video

Time for new T-CON board unless you want to troubleshoot it further.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Time for new T-CON board unless you want to troubleshoot it further.

I think with the possibility of getting a t-con board for £5-£20 is a better shot than me trying to troubleshoot it, as I don't have the skill or equipment, or eyesight to work on these small components.

I'll order a t-con board, and report back when I get it.

Thanks again to all for the help and pointers.

[tmcw]

Re: Panasonic TX-48CX400B - No Video

Ok, so I got another t-con board, but I have the same issues as before, sound but no picture.

Testing the voltages on the new t-con board, I'm seeing more or less (+/- 0.03V) the same voltages as noted a few posts above.

I went back to the power board, at the connection (CN4) that goes to the mainboard, and apparently I'm not getting what I think should be the +5V_STBY, this is what I'm getting on the pins (hope I've assigned the voltage to the correct pin)...

1 24.8V
2 0.01V
3. 0V
4. 0V
5. 3.2V
6. 0V
7. 1.6V
8. 0V
9. 0V
10. 11.8V
11. 11.8V
12. 11.8V

I've attached the 071114 R9 schematic, but it doesn't show the CN4 pinout, I got the CN4 pinout from the R6 schematic, so assuming it would be the same.

But the mainboard would not be using 5V standby for generating video, would it, surely it would be using the 12V?