Chosen Solution
I have a Samsung UN55KU6290 that has a black screen, voltage on standy drops every few seconds and USB ports on main board drop as well (tested with a good cable) power supply seems to be making enough power but it drops on assuming before LEDs can power on. No bulged or popped capacitors, burns or anything kind of stumped anything helps
Hi @nick7847 , Are there any images to be seen on the screen if you shine a torch at an angle close to the screen when the TV is trying to turn on? Try the following: Disconnect everything from the TV including the power. Remove the back cover and then disconnect the cable between the mainboard and the power board. Reconnect the power to the TV. The screen’s LED backlights should turn on and stay on. There will be no pictures because the mainboard is disconnected. If the backlights stay on measure the voltages on the power board at the connector where the mainboard cable was connected to. Their values should be marked on the board near the connector. If the voltages are OK it may be a mainboard problem or a mainboard-powerboard cable problem. Use an Ohmmeter to test each wire in the cable for continuity to eliminate it as a possibility. Do this with the cable out of circuit If the backlights blink or don’t turn on then there is a problem either in the backlights or in the power board. Measure the voltage between the LED +ve leads and earth on the power board. If the voltage is >230V DC the problem is in the LED array or the connection to the array from the power board. If the voltage is <50V DC it is most likely in the power board. Be safety aware when testing on the power board as there is exposed lethal AC voltage on the board when the power is connected
@Ryan M Usually power supply voltages don’t fluctuate so it sounds like a problem with the board. Reconnect everything back to normal and them check if there is 12.35V DC at the STB (standby) voltage reference point on the power board, when power is connected to the TV. The power board signals the mainboard with the STB voltage to indicate that power is available to the TV and it is the mainboard that turns on the red standby power LED. Here’s an image of the board that shows where it is.
(click on image). It seems too high a value for a standby voltage as other Samsungs are usually 7.5V STB and 13V On when they have a combined reference point as this model has (it also says STB/On). i.e. 7.5V in standby, 13V when the TV is on, when measured at the same point and this is usually printed on the board near the STB ref point, but not on this board it seems as it only shows the one voltage value.. Whatever, the point is that it must be a steady voltage. If fluctuating, I’d change the board.
