LG 50lb6300 voltages are reversed

[nwcs]

This TV came in with the picture flashing rapidly on and off. I tested the LED's and they are fine. I then checked to voltages to the led's from the power supply and the voltages were changing from high to low on led+ on the left and changing too fast to tell what voltage's were on led+ on the right. Has anyone ever seen this before?

[nwcs]

Re: LG 50lb6300 voltages are reversed

I forgot to add that the some of the voltages to the main board from the PS are reading negative. I found pins 1,2,3,5,6,7,9,10,11,14 and 17 are all in the negative. sorry,

[budm]

Re: LG 50lb6300 voltages are reversed

You have tow boost converter circuits for two LED strings.
The two LED strings are not the same size.
How about good clear straight shots of the whole top and bottom side of the board?
Also what Voltages did you test on the connector of the power supply board that goes to the main board, what are they? You need to put down pin name of each pin and follow by the Voltage reading.

[budm]

Re: LG 50lb6300 voltages are reversed

I forgot to add that the some of the voltages to the main board from the PS are reading negative. I found pins 1,2,3,5,6,7,9,10,11,14 and 17 are all in the negative. sorry,

Connector has pin name for each pin, so what did you use for GND?
That has to be reading error.

[nwcs]

Re: LG 50lb6300 voltages are reversed

I do not know why my answer to your last question did not post but here it is again. I put the ground on one of the screws on the back frame.
1 is pwr-on -
2 drv-on
3 3.5v
4 p-dim1
5 3.5v
6 3.5v
7 gnd
8 p-dim2
9 24v
10 24v
11 gnd
12 gnd
13 12v
14 12v
15 12v
16 nc
17 and 18 gnd
even the grounds show neg voltage.

[budwich]

Re: LG 50lb6300 voltages are reversed

the point that you are using for "reference" which is the black lead IS NOT at ground potential (most likely floating) and hence any measurement to that "reference" is probably not going to be what you are looking for.

you can verify ALL your ground points and other areas with the set unpowered / unplugged and measure resistance between various "ground points" that you think should be grounds. They should all measure "0". Once you have determine that, then you can proceed to measuring things again.

[nwcs]

Re: LG 50lb6300 voltages are reversed

I did that and it is a good ground point

[budwich]

Re: LG 50lb6300 voltages are reversed

check your batteries in the meter... maybe.

you checked the resistance between the "third pin" on the power in connector with rest of set grounds. Further, you checked the power cable.

[budm]

Re: LG 50lb6300 voltages are reversed

Just to be clear, you are saying that the 3.5V, 12V, and 24 all shown as - 3.5V, -12V, -24V? Can we see the probes hookup and the screenshot of the meter display?
All the boards are screwed down, correct?

[nwcs]

Re: LG 50lb6300 voltages are reversed

I should add that when I first turned it on the tv worked fine and it took several days to start to strobe and guess what it is now working just fine and most likely will for days.

[budm]

Re: LG 50lb6300 voltages are reversed

Turn down the backlights level on all input to as low as possible to see if it has any affect on the symptom.

[nwcs]

Re: LG 50lb6300 voltages are reversed

I will and run it for days again to see if it fails

[nwcs]

Re: LG 50lb6300 voltages are reversed

I turned down the backlight on all inputs to 50% and it ran fine for one day. I turned it on this morning and back to the same problem. I ordered a power supply since the main board is not available and I will hope that is it.

[R_J]

Re: LG 50lb6300 voltages are reversed

I suspect the ground screws are not power supply ground, Use P205 or P204 near T101 transformer for ground, or use heatsink (HS4)

[frannyjunk]

Re: LG 50lb6300 voltages are reversed

I turned down the backlight on all inputs to 50% and it ran fine for one day. I turned it on this morning and back to the same problem. I ordered a power supply since the main board is not available and I will hope that is it.

Did the new power supply board fix it?

[nwcs]

Re: LG 50lb6300 voltages are reversed

No, it ended up being the main board. I did fix it and it is out the door.

[frannyjunk]

Re: LG 50lb6300 voltages are reversed

No, it ended up being the main board. I did fix it and it is out the door.

Do you remember if you replaced the board, or just a component? If component, which one? Thanks!