Samsung UE55H7080 black screen (sound is working)

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

OK... now that "we" are talking the same thing in terms of tests, it would appear that there is an issue at the tcon to panel area... maybe. As "normally"... but maybe not for samsung / model, but when a panel is powered correctly and one of the tcon to panel cables is disconnected, the disconnected side shows white. Having said that, some sets like sony, if the panel connection is not there, then the system detects this and shut down. What happens to the sound when you do this test (tcon to panel disconnect)?

Further, your "other test" (removing the main to tcon cable) causes the backlights to turn on.... again a different observation than what started this thread and title.... so did you then redo your measurements at the power board to see what is different?

Please remember that the forum can only help you if you provide clear and concise answer as the forum can't see your set or your testing.

I'm sorry if it was unclear but that the backlight is working at all came up during the tests recommended here. I didn't know that when I was starting the thread.

I repeated the experiments and made a table of the results (see attachments). I always disconnected one cable at a time, so 3 were plugged, 1 was unplugged for this tests.

Maybe check those little capacitors on tcon for shorts, diode mode one probe on each side, if you find one shorted, could indicate a problem on driver board between tcon and panel.

In a particular area of the tcon board? There are a lot of capacitors on there.

OK, let me get this straight:
If you have both of the ribbon cables between the LCD panel and the T-CON board disconnected, and the cable between T-CON and the main board is still in place then the backlighs will be on when turning the TV ON, correct?
If that is the case the put the ribbon cables back in place and then check the resistance between GND test points VGH, VGL, VCOM, VCC, VDD,... to see what you get and report the readings.

When disconnecting both ribbon cables which go to the panel (marked with Ex3 and Ex4 in this attachment) and keep the cables marked with Ex1 and Ex2 plugged, the screen stays black, hence the backlight stays off.
Where can I find VGH, VGL, ...? I can't find these writings on the tcon board.

[budm]

Re: Samsung UE55H7080 black screen (sound is working)

OK, let me get this straight:
If you have both of the ribbon cables between the LCD panel and the T-CON board disconnected, and the cable between T-CON and the main board is still in place then the backlighs will be on when turning the TV ON, correct?
If that is the case the put the ribbon cables back in place and then check the resistance between GND test points VGH, VGL, VCOM, VCC, VDD,... to see what you get and report the readings.

[nomoresonys]

Re: Samsung UE55H7080 black screen (sound is working)

Maybe check those little capacitors on tcon for shorts, diode mode one probe on each side, if you find one shorted, could indicate a problem on driver board between tcon and panel.

[budwich]

Re: Samsung UE55H7080 black screen (sound is working)

OK... now that "we" are talking the same thing in terms of tests, it would appear that there is an issue at the tcon to panel area... maybe. As "normally"... but maybe not for samsung / model, but when a panel is powered correctly and one of the tcon to panel cables is disconnected, the disconnected side shows white. Having said that, some sets like sony, if the panel connection is not there, then the system detects this and shut down. What happens to the sound when you do this test (tcon to panel disconnect)?

Further, your "other test" (removing the main to tcon cable) causes the backlights to turn on.... again a different observation than what started this thread and title.... so did you then redo your measurements at the power board to see what is different?

Please remember that the forum can only help you if you provide clear and concise answer as the forum can't see your set or your testing.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

Jeesh, where did you indicate that you disconnected the ribbon cables one at a time as suggested. Disconnecting the connectors on the opposite side indicates you are not doing the correct test. The first half of this thread is trying to determine if your backlights come on or not.


Assumes you only checked one side.


Assumes you disconnected both at the same time.

I see what you mean. After the post from budwich #17 I anyway tried disconnecting also the bottom connectors to the panel (which I also tried to tell in my post). Sorry for the confusion.

I disconnected always one at a time from the bottom two connectors and neither with the right cable connected, nor with the left one connected I can see something on the screen. It stays black.

[neilc6]

Re: Samsung UE55H7080 black screen (sound is working)

Jeesh, where did you indicate that you disconnected the ribbon cables one at a time as suggested. Disconnecting the connectors on the opposite side indicates you are not doing the correct test. The first half of this thread is trying to determine if your backlights come on or not.

Nothing changes when I disconnect one of the bottom two ribbon cables.

Assumes you only checked one side.

By disconnecting the bottom cables, nothing (obvious) changes.

Assumes you disconnected both at the same time.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

You need to disconnect the two ribbon cables going from the tcon to the panel one at a time. NOT the two connectors you highlighted in red in post #18 you described as top connectors. If one side is working, then there is a panel fault on one side.

Man, I wrote the following:

"When I disconnect one of the top cables (see red areas in attachment) of the tcon board, the backlight turns on as I switch on the TV. The backlight also turns on if both cables are disconnected. By disconnecting the bottom cables, nothing (obvious) changes." in Post #18. There I only referred to the attachment when I was talking about the two cables on the TOP. I've also disconnected the two ribbon cables at the bottom and like explained twice now, everything stays dark when I disconnect the either of the two BOTTOM ribbon cables (I marked them for you now too in the attachment in this post).

[neilc6]

Re: Samsung UE55H7080 black screen (sound is working)

You need to disconnect the two ribbon cables going from the tcon to the panel one at a time. NOT the two connectors you highlighted in red in post #18 you described as top connectors. If one side is working, then there is a panel fault on one side.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

You need to disconnect the ribbon cables with the flip lock one at a time to see if half of the panel is working. This thread may apply https://www.badcaps.net/forum/showthread.php?t=50646

Like explained above, I did this (at least for the tcon board). Nothing changes when I disconnect one of the bottom two ribbon cables. When I disconnect either the top ribbon cable or the other cable with 6 connections, the backlight turns on.

I've spotted a 3rd LED (LED2) on the tcon board which stays off all the time. Don't know if this helps.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

How can you conclude that now? Shouldn't a panel failure be better visible on the screen?

[neilc6]

Re: Samsung UE55H7080 black screen (sound is working)

You need to disconnect the ribbon cables with the flip lock one at a time to see if half of the panel is working. This thread may apply https://www.badcaps.net/forum/showthread.php?t=50646

[MixyourMind]

Re: Samsung UE55H7080 black screen (sound is working)

Panel Failure, H 7000 and 8000 series from Samsung suffer from bad design and display driver failure.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

When I disconnect one of the top cables (see red areas in attachment) of the tcon board, the backlight turns on as I switch on the TV. The backlight also turns on if both cables are disconnected. By disconnecting the bottom cables, nothing (obvious) changes.

If you need any information about voltage levels, just let me know in which ones you're interested in.

[budwich]

Re: Samsung UE55H7080 black screen (sound is working)

disconnect, one at a time, the cables going from the tcon to the panel see what the result is (note: cable changes with POWER OFF).

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

I've checked the voltages on the CNM803 now after switching on the TV
N.C. 0V
P_DIM4 0V
P_DIM3 0V
P_DIM2 0V
GND 0V
P_DIM1 0V
A13V 12.6V
OD_ON/OFF 3.2V
A13V 12.6V
OD_LEVEL 0V
A13V 12.6V
BLU_ON/OFF 4.8V
A13V 12.6V
PS_ON 3.2V
A13V 12.6V
GND 0V
GND 0V
GNV 0V
Vamp 12.6V
Vamp 12.6V
Vamp 12.6V
GND 0V

I have to note that I don't have an oscilloscope at home right now, so I only can check the voltages with a simple multimeter. What makes me wonder is, that the P_DIMx Signals are 0V. But if they are actually PWM signals I might have problems measuring them with the simple multimeter?

I've checked the fuse at the T-con board (at least I think that this is the fuse; attachment) and this one is okay. The two LEDs on the T-con board light up blue after switching on the TV.

[nomoresonys]

Re: Samsung UE55H7080 black screen (sound is working)

Just for fun check the tcon fuse, make sure it isn't blown and see if you have voltage on each side, negative probe on ground positive on each side.

[budm]

Re: Samsung UE55H7080 black screen (sound is working)

https://www.badcaps.net/forum/attach...3&d=1557584044
1) The power supply/LED driver board has pull-up resistors for the PS-ON (CNM803 pin 14), BLU_ON/OFF (same as BL-ON, CNM803 pin 12), P_DIM 1 ~ 4; the pull-ups are there to keep those control pins HIGH for power supply/LED driver board self test. When the main board is connected to the power supply board and TV is not yet turned on, those controlled pins will be kept low by the main board, and the PWM in this case will be kept low by the T-CON board since T-CON board controls the backlights level in this TV model, you can see the wires from T-CON board to the power supply board connector CNM803, Samsung calls this "Samsung’s segmented dimming technology" so they can claim fake high dynamic contrast ratio.
2) When all the connectors are back in place you need to report the Voltage of each pin of the CNM803 of the power supply board so we can see if all the control signals are present or not, right now the BLU_ON/OFF is OK but we do not know if we have the PWM signals or not, these PWM 1 ~ 4 are used for controlling the backlights level, so report all the pin's Voltages, you MUST, REPEAT MUST put down the pin name and follow by the Voltage reading for each pin when TV is turned on so we can easily see what you have and do not have on those pins.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

Sadly I also don't have a service manual. Is there any way to get one?

What makes me suspicious is, that the BLU_ON bin shows 3.2V when the connector is disconnected (hence, the LEDs are on; as explained above) and the 4.6V when the plug is connected and the TV is switched on.

Should the integrated driver be a IC on the power supply board?

So to follow the path I would have to remove the power supply board from the TV and follow the paths on the bottom. Or have you thought of any other way?

[yokoono]

Re: Samsung UE55H7080 black screen (sound is working)

Another pin for bl-on does not see what it would be like. If the voltage increases at startup is correct because I think that the pine and the input to the integrated driver must be at least one transistor. Start from the bl / on pin to the integrated driver and see if the command reaches its starting pin. I do not know what is integrated and I do not even have the service manual.

[Steradiant]

Re: Samsung UE55H7080 black screen (sound is working)

OK. If that is the pin you are looking for, it means that the motherboard gives the command to backlight. The command follows a route and arrives at the LED driver. Measure if that command arrives and if something is not interrupted.

You write "if". I honestly can't tell if this is the pin I'm looking for.

Furthermore, you wrote that the voltage should go from high (approx 3V) to low (0V) when switching on the TV. This pin shows the opposite behavior though.