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I tried a lot - measured the power board with a multimeter, bought a new power board (KB116WJQZ), measured power supply, baked the motherboard in the oven - nothing, no standby light, no power.
I'm not quite ready yet to give up on the TV, so does anyone have any idea what to try next?
Thanks
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There has to be a voltage from the power board to the mainboard.
Perhaps when the new power board arrives, do not connect any cables to it except the AC power cable and check for voltage on the PD connector pins, presumably only the AC Det or STB pins
That way with no other cable connected to it, there's nothing that can damage the power board.
If there is none then the power board is not providing initial standby power to the mainboard for some reason
Can't imagine why especially if it happens with a 3rd power board, unless the board is shorting out to the chassis where it shouldn't be i.e. not at designated earth point on the board through a screw connection but somewhere else where it may be touching the chassis.
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@jayeff good point, will try to measure the 3rd power board before connecting with the other connectors - it would be an explanation, however I don't think it shortens out anywhere since there is a insulation mat below the power board and they only rest on the designated crew pillars that create the ground.
Also was wondering why the TV doesn't have a ground - it only uses a 2 pin plug??
Ground (aka earth) is relative.
Once the AC power is rectified to DC on the power board the +ve DC output is the supply and the -ve DC is the common (or earth) return path.
So the chassis will be connected to the -ve side of the DC power output.
Like a car battery, the +ve is the power supply, the -ve is connected to the chassis as a return path aka earth.
Any point that is measured for voltage with the meter connected between it and an earth point (or chassis) will be +ve with respect to or relative to the -ve side of the DC supply i.e. how much voltage is still there after the current has passed through components to get to that point.
Knowing Ohm's Law is fundamental in understanding how electrical circuits work
@jayeff I received the replacement for the replacement power board today, on that one I could measure the 5V supply voltage. So I built it into the TV and it works again. Super happy, thanks for your help!
@jayeff It was on the BU5V, and accessible from the top ;)
Thx
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@joejonson give us more information about this "and is completely dead". Are you saying that there are no signs of life? No power LED etc.? You said you have a new power board and "measured power supply". Where did you measure and what were the results? Do you get power to the center unit and did you check your AC cable? Your new power board is a RUNTKB116WJQZ what are the outputs on connector PD?
por oldturkey03
@joejonson,
What voltages are on PD-13 (AC Det) & PD- 24 (STB) of the power board?
Do you get the same voltages (if any) on the same pins of the PD connector on the mainboard?
por jayeff
@oldturkey03 sorry for the late response: Yes, no signs of life, I have 120V on the power cable pins, fuse is intact, but pressing of any buttons etc. does not light up LED etc. I saw in a video that if you unplug the main board (PD connector) the LEDs should be on, tried it nothing.
And yes, the part numbers and models of the power board are the same - don't think I overlooked something there.
@jayeff
I don't know if did anything wrong measuring the PD connectors but I didn't get any voltage there - had my multimeter on 20V DC put black on the housing of the TV and the red on on the pins and didn't get anything?! Was that correct?
[image|2772687][image|2772686]
por JoeJonson
@joejonson
I was just looking at the info printed on the board next to the PD connector.
You can only access the odd numbered pins easily on the top of the board so pin 24 is hard to get to unless you unplug the cable, or remove the board from the chassis and support it whilst measuring the even pins on the underside
With most other brands the STB voltage is the standby voltage sent to the mainboard to indicate that power is available (the mainboard turns on the standby power LED)
There also being an AC Det pin (AC Detect?) might do the same thing. Either way there should be some voltage from the power board to the mainboard when the power is connected to the mainboard. The power board doesn't control the TV the mainboard does.
You may have to take a step back and ensure that there's AC power through the fuse on the power board
por jayeff
@jayeff Hi Jayeff, you reply fast :D - unfortunately there is no labeling of the pins on that board except of PNL12V, SGND, BU5V - the underside is also not labeled - so should I unscrew the board, take the connectors out and measure the Voltage between the two rows of connector pins with 20 VDC?
Thanks
por JoeJonson
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