Samsung UE75MU7009TXZG Endless Power Cycle
Hi everyone and thanks in advance for any help I might get here
My Samsung TV is about 4 years old. The exact model number is UE75MU7009TXZG.
About half a year ago I started seeing occasional green frames pop up while watching movies. I mean literally green frames. Not the image turning green, but the entire screen turning green for a split second. This happened maybe once or twice during a 2 hour movie. So no big deal, but clearly something was not quite right.
Since a few days, the TV won't turn on anymore. I removed the back-cover to take a look at the internals, in the hope of spotting one of these bad capacitors that Samsung seems to be quite famous for.
Unfortunately all the capacitors seem to be in good order. While the TV was open, I powered it up, just to see what would happen. Here is the exact sequence of events:
1) Connect the power cord -> The little red LED at the lower right hand corner of the TV turns on (meaning the TV is in stand-by)
2) Press the power-on button (either on the TV or on the remote) -> something on the power board makes a "click" sound and on the Backlight Control Board three blue LEDs turn on.
3) For about 5-10 seconds, nothing happens. Then the power board emits a "click" sound, the blue LEDs on the Backlight Control Board turn off. Immediately afterwards there is another "click" from the power board and the blue LEDs on the Backlight Control Board are on again. This cycle repeats for as long as the TV is powered.
While the TV is powered up, there is no image showing up on the screen. The backlight LEDs also never turn on.
I tried disconnecting various cables to see if any of them have an impact on the behavior of the TV.
When I unplug the 20 pin cable that is connected to socket CNM803 (on the power board), this has quite an impact:
1) Connect the power cord -> power board makes "click" and all the bright white backlight LEDs come to live. No more power-cycling, the TV just stays in this state until I disconnect the power cord.
The voltages on CNM803 seem ok. According to the printed table next to the connector, there should be a bunch of 12 V and 18 V lines. Multimeter measurements confirm that these voltages are present (12.8 V and 18.0 V), regardless of CNM803 being connected or disconnected. In case CNM803 is connected and the TV is in stand-by, the voltage of the 12 V line is reduced to around 8.5 V, which is in line with the stand-by value listed in another table on the power board. As soon as the TV goes from "stand-by" to "on", the voltage goes up from 8.5 V to 12.8 V.
Thermal imaging of the power board reveals no particular hot-spots. The VRMs that are attached to the heatsinks are going up to around 30 degrees C, and one resistor lights up a bit as well (not as hot as the VRMs though). Otherwise the board and the components stay close to room temperature.
Some additional information regarding the TV:
* The TV was attached to the wall with a VESA mount bracket for almost its entire life
* The TV was connected to a master/slave power distribution unit. It was a slave (the AVR was the master).
* The TV was basically a glorified monitor: usually it would just display whatever video signal it gets from the AVR. Maybe 1% was spent watching Netflix or Youtube directly through the TV.
* As mentioned in the introduction, completely green frames started to be inserted at random while watching movies. It is unclear if this was caused by something in the TV slowly breaking or if it was a problem of the AVR or the media center.
What would be the next debugging step?
Hi everyone and thanks in advance for any help I might get here
My Samsung TV is about 4 years old. The exact model number is UE75MU7009TXZG.
About half a year ago I started seeing occasional green frames pop up while watching movies. I mean literally green frames. Not the image turning green, but the entire screen turning green for a split second. This happened maybe once or twice during a 2 hour movie. So no big deal, but clearly something was not quite right.
Since a few days, the TV won't turn on anymore. I removed the back-cover to take a look at the internals, in the hope of spotting one of these bad capacitors that Samsung seems to be quite famous for.
Unfortunately all the capacitors seem to be in good order. While the TV was open, I powered it up, just to see what would happen. Here is the exact sequence of events:
1) Connect the power cord -> The little red LED at the lower right hand corner of the TV turns on (meaning the TV is in stand-by)
2) Press the power-on button (either on the TV or on the remote) -> something on the power board makes a "click" sound and on the Backlight Control Board three blue LEDs turn on.
3) For about 5-10 seconds, nothing happens. Then the power board emits a "click" sound, the blue LEDs on the Backlight Control Board turn off. Immediately afterwards there is another "click" from the power board and the blue LEDs on the Backlight Control Board are on again. This cycle repeats for as long as the TV is powered.
While the TV is powered up, there is no image showing up on the screen. The backlight LEDs also never turn on.
I tried disconnecting various cables to see if any of them have an impact on the behavior of the TV.
When I unplug the 20 pin cable that is connected to socket CNM803 (on the power board), this has quite an impact:
1) Connect the power cord -> power board makes "click" and all the bright white backlight LEDs come to live. No more power-cycling, the TV just stays in this state until I disconnect the power cord.
The voltages on CNM803 seem ok. According to the printed table next to the connector, there should be a bunch of 12 V and 18 V lines. Multimeter measurements confirm that these voltages are present (12.8 V and 18.0 V), regardless of CNM803 being connected or disconnected. In case CNM803 is connected and the TV is in stand-by, the voltage of the 12 V line is reduced to around 8.5 V, which is in line with the stand-by value listed in another table on the power board. As soon as the TV goes from "stand-by" to "on", the voltage goes up from 8.5 V to 12.8 V.
Thermal imaging of the power board reveals no particular hot-spots. The VRMs that are attached to the heatsinks are going up to around 30 degrees C, and one resistor lights up a bit as well (not as hot as the VRMs though). Otherwise the board and the components stay close to room temperature.
Some additional information regarding the TV:
* The TV was attached to the wall with a VESA mount bracket for almost its entire life
* The TV was connected to a master/slave power distribution unit. It was a slave (the AVR was the master).
* The TV was basically a glorified monitor: usually it would just display whatever video signal it gets from the AVR. Maybe 1% was spent watching Netflix or Youtube directly through the TV.
* As mentioned in the introduction, completely green frames started to be inserted at random while watching movies. It is unclear if this was caused by something in the TV slowly breaking or if it was a problem of the AVR or the media center.
What would be the next debugging step?
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