Lg 50pk950 turns on by itself (stumped!)

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

ok, lets try something different.

locate the power on pin that goes to the main from the button and sub boards.
what does it read in stby. is the voltage fluctuating from the word go? then monitor that voltage till it powers up, annoying, but could prove interesting. it has to get its command from those boards, i can't see it being the main.

Thank you, that's a good idea and I will probably do that next, but right now I'm doing tests with the IR sensor covered up.

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

Update: Since covering the IR sensor, the TV has not turned on by itself in the 2 times I've left it plugged in for about an hour. Promising, but I'm hesitant to believe it! I uncovered the IR sensor and it turned itself on in the usual 15 minutes. On my 3rd test session now with IR covered. We'll see what happens. I'm trying to figure out how this makes sense because the IR sensor must not be bad or it would have caused my friend's TV to turn on by itself when it was in his. Do you guys think it could be giving false feedback to the main board by way of an intermittent wire in the harness from the SUB to the main board?

[dskall]

Re: Lg 50pk950 turns on by itself (stumped!)

Maybe fluctuating 3.3v or cap on main. I think something on main board affecting circuit

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

Update: It's still turning on by itself with the IR covered.

Maybe fluctuating 3.3v or cap on main. I think something on main board affecting circuit

Yes, I think something like a fluctuating voltage like that might be the issue, but would that have allowed this main board to work fine and not cause self power-up in my friend's TV? Maybe because it's a combination of issues or something to do with the cable in between the main board and the SUB board? I need to check each wire for continuity and test for fluctuating voltages when the TV is in standby.

Can anyone again suggest which voltages I should monitor and where would be the best to probe?

[dskall]

Re: Lg 50pk950 turns on by itself (stumped!)

You sure it was not turning on with sub disconnected. Not just coincidence.

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

You sure it was not turning on with sub disconnected. Not just coincidence.

I tried several times leaving it for hours with SUB board disconnected and it never came on, but I could try again while I'm waiting for something else to check. I would like to get a confirmation on what voltages to monitor and at which test point in the meantime.

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

Also, I just checked for continuity on each wire of the cable between the main board and the SUB board and everything was okay, but of course it's possible that one of the wires could be intermittent; it's hard to move them around and test at the same time to see if something is intermittent in that way.

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

ok, lets try something different.

locate the power on pin that goes to the main from the button and sub boards.
what does it read in stby. is the voltage fluctuating from the word go? then monitor that voltage till it powers up, annoying, but could prove interesting. it has to get its command from those boards, i can't see it being the main.

I'm not seeing which pin, can you help me identify? I think my 2 pictures of the SUB board are good enough to show, right?

[dskall]

Re: Lg 50pk950 turns on by itself (stumped!)

Running out of ideas. If you have min/max meter you could monitor on/off pin to see if signal is originating. Does it have wifi? Have had strange things go on with wifi modules. When you unplug sub are you unplugging at main or sub?

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

Also, I've noticed that if you touch certain areas of the SUB board (just handling it to cover and uncover the IR sensor with tape), the TV will turn on all by itself. I made sure it wasn't moving the cable going to it from the main board that was doing this and I also tried the other SUB board I have and it acts the same way. I think my body is just giving it the input it gets from the capacitance keypad (even though it is unplugged) near the traces for the ribbon cable plug for the keypad. What I'm wondering is if something is giving it this same false input and if there's some way to test this or isolate this.

Also, I found that my method of covering the IR sensor with masking tape was not sufficient to block IR beams; I tried a remote and it worked right through the masking tape. I could use a different type of tape or method, but I'm wondering if the IR problem theory is not necessary to explore? Ideas? Anyone? Thanks in advance!

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

Running out of ideas. If you have min/max meter you could monitor on/off pin to see if signal is originating. Does it have wifi? Have had strange things go on with wifi modules.

My Fluke does have min/max, but which pin is the on/off one? I'm not sure what it would be marked; how can I identify it?

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

There are 9 test points on the back of the board, would one of these be the on/off point you are referring to? They are:

IR
KEY 1
KEY 2
LED-RED
SCL
SDA
3.3VST
GND
3.3V

(See my pictures in post #2)

[dskall]

Re: Lg 50pk950 turns on by itself (stumped!)

Your on/off key presses should change voltages on one of the wires. Is there any missing shielding or grounding. Still wonder if mainboard doesn't factor in to this somehow

[dskall]

Re: Lg 50pk950 turns on by itself (stumped!)

key1 or key2

[dskall]

Re: Lg 50pk950 turns on by itself (stumped!)

You also have an scl and sda which are multiplex. What they are interfacing with I don't know. As I am reaching limits of my skillset here I hope someone with more knowledge will contribute.

[sam_sam_sam]

Re: Lg 50pk950 turns on by itself (stumped!)

I am wondering if the IR module is having issues because you say that if you cover it dose not turn on by it self

Just a thought

[dick_barton]

Re: Lg 50pk950 turns on by itself (stumped!)

A long shot but have you checked to see if there is any AC (or high frequency smps) ripple on any of the DC lines. This could be due to a leaky diode(s) or duff capacitor(s) and could be the cause of the problem you have.

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

I am wondering if the IR module is having issues because you say that if you cover it dose not turn on by it self

Just a thought

Thank you, but I posted an update after that that it WAS still turning on by itself, it just didn't the first few tries. Also, I later found that the masking tape I was using wasn't blocking a remote signal, so I might retry the tests with a better cover, but will pursue the other tests first.

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

key1 or key2

Does it matter which one I use? And I'm just going to be monitoring a voltage on one of those points and set my meter to min/max and wait for the TV to turn on by itself?

[Truncatedhose]

Re: Lg 50pk950 turns on by itself (stumped!)

A long shot but have you checked to see if there is any AC (or high frequency smps) ripple on any of the DC lines. This could be due to a leaky diode(s) or duff capacitor(s) and could be the cause of the problem you have.

Thanks for chiming in! No, I have not checked for that. Any suggestion on exactly where to start? Just put my meter to AC and see what is on the VS, VA, Stby, etc.? Or something else?