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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
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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
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When i tested the board with connectors off i was getting a periodic voltage drop on all pins, (8v to 13v and back again) on the 18 pin connector to the main board while the standby light blinks when the tv tries to power on. Voltage to the led array was low when everything was plugged in (below 100v) Also there is a ticking from the regulator about every 2 seconds like its trying to power up but fails, CP807-6 is reading 400-450v no change. Regulator still ticks when main board is unplugged and no backlight probably due to this power loop
The backlights should turn on and stay on when the mainboard is disconnected.
What is the voltage between the LED+ve lead and earth when the setup is as above?
If there is varying or low voltage at the LED connector then it is a power board problem. If there is steady or ramping up to high voltage then the power board is driving the voltage as high as possible trying to turn on the backlights, so it may be in the backlights.
@jayeff voltage to LED array voltage was about 150-170v, Even with everything disconnected it does not want to give steady voltages at the 18p connector to mobo (with connector removed so no power to mobo)
(Every pin with voltage on hot side of the ps board drops to standby 8v then climbs back up again 13v every few seconds) you can clearly hear mobo and ps board getting power for a second then silence and repeat. Its a cycle you, would think wouldn’t happen with a new power cord and new PS board an
Flashing standby light whenever tv tries to power on
Standby voltage periodic drop from 13v ON to 8v STBY
TIcking from voltage regulator when tv tries to power on
No black lights when mobo disconnected
Hi @nick7847
With the mainboard being disconnected from the power board it means that it is not interfering with it so to speak so the voltages should be steady and the backlights should be on as well.
I don’t know unless the new power board (is this correct?) is also faulty
I would have thought that at 150-170V that the backlights should be on.
Perhaps you may have to invest in a LED backlight tester - examples only to prove that the LED's are OK and that they're not causing the problem. The tester can test if the backlights are OK without the need to have power applied to the TV.
Update upon checking LED voltage with new board it now goes from 70v to 320v every few seconds plugging in LED array seems to makes no difference to voltage reading
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@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.
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My multimeter jumps between ~5 and ~15 VDC when measuring between the + and -13 point next to it whether it is connect to the LED and mainboard or not. I'm not sure if there is a better reference point to test it against.
Could the board be rapidly switching between standby and on?
@Ryan M
It could be switching on/off but whether this was due to the mainboard or the power board, I don't know.
Try disconnecting the IR sensor/TV Power On button board (if they're on the same board) from the mainboard and then check the STB voltage on the power board to see if it stays steady. This is just in case one of the controls is faulty telling the mainboard to turn the TV on/off repeatedly
Not sure what you mean by the -13 point next to it.
Is the STB ref point just a convenient location to test as it is actually an even numbered pin on the connector that cannot be accessed without removing the cable ?
You should be measuring between the ref point and an earth (screwhead perhaps)
On the photo you linked, you can see a similar exposed point near by labled -13 VDC, but I repeated with a screw and got similar behavior. This behavior is consistent with the IR sensor/power on disconnected, the main board disconnected, and the LEDs disconnected.
I suppose this seems pretty straight froward to be power supply related. I appreciate your help. I will updated if a new power supply solves the issue.
As a note, do you have a recommended source for buying a new power supply?
@Ryan M
Try to get a power board from a supplier that offers a good returns policy if the board is not the problem i.e. full refund or minimal restocking fee.
Also if getting a board off Ebay etc, check the seller's 'reputation" %.
Personally i avoid any with a rep <99.5 but that's just me.
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