LG 60LB7100 screen goes black seconds after start up

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

LED+78.6 all the VC we're the same as before.

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

budm I did leave the meter ground to the chassis and put the positive to each positive side of both LED+ VC+. I'm kinda thinking the back lights are good. Uncertain though. Waiting for your knowledge on this.

[budm]

Re: LG 60LB7100 screen goes black seconds after start up

budm I did leave the meter ground to the chassis and put the positive to each positive side of both LED+ VC+. I'm kinda thinking the back lights are good. Uncertain though. Waiting for your knowledge on this.

Do you mean VC_X (I.E. VC_1, VC_2,....VC_6). I cannot see how you ca have VC_x higher than the feeding Voltage (LED+).

[sean0118]

Re: LG 60LB7100 screen goes black seconds after start up

Are you sure that the multimeter is working and the DC voltage setting is selected?

If your unsure, confirm by measuring the voltage of a 9V battery or similar.

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

I tested the meter on my truck battery and got 12.2 so I believe I have the correct setting. The LED+ and all the VC 1-6 were at 78.6 on start up.

[sean0118]

Re: LG 60LB7100 screen goes black seconds after start up

These two pins for LED+ and LED-?

I'm just looking through the thread again to try to understand, what do you mean by LED-? I can't see anything with the label, or do you mean GND?

[sean0118]

Re: LG 60LB7100 screen goes black seconds after start up

I've attached a circuit based on budm's description (I might be wrong).

Each LED represent 100 or so in series, so the voltage at VC_1 is LED+ minus the voltage drop over the first string of LEDs. So it must be less than LED+ unless something is horribly wrong...

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

Here's a picture of the meter setting I'm using and the other picture is from the old board but shows where I tested the LED+ and the plug to the left I tested all 1-6 VC's positive. Results were LED+ 78.7v and 55.8v after the lights were off. All 1-6 VC were the same 78.6v down to 55.9v. Maybe I'm testing the wrong spots for VC?

[budm]

Re: LG 60LB7100 screen goes black seconds after start up

Where did you put the black probe of the meter?

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

I kept it in a screw hole right above the board. I'm assuming it's the chassis. The screw hole is in the big sheet metal backing of the screen that all boards attach to.

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

I'm running out of time to send the inverter board back if this isn't a back light problem.

[sean0118]

Re: LG 60LB7100 screen goes black seconds after start up

Interesting... sounds like you're doing it right. What's the resistance (when OFF) from LED+ to each VC?

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

I tested resistance from LED+ to each VC+ and got 0.00. then I tested LED+ to each VC- and got 46.7 and 46.6 through out all 6 VC's. Maybe I'm testing wrong with meter setting? My experience with anything electrical is mostly from competition car audio and minor computer upgrades. So this is my first go on trying to save an 1,800 dollar TV.

[sean0118]

Re: LG 60LB7100 screen goes black seconds after start up

I might be missing something, but there is no VC+ and VC-, only VC, which is the cathode voltage of the LEDs. LED+ is the anode voltage. The pins of that 14pin connector alternate between LED+ and each of the six VC lines.

[RJARRRPCGP]

Re: LG 60LB7100 screen goes black seconds after start up

Damn! Seems that LED tvs are no better than CCFL tvs from the Core 2 era.....(also that was the classic bad cap tv era) (2006-2009)

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

sean0118. Thank you for explaining that. I had to magnify the picture of my board to see that. I'll be re testing after a while now that I know exactly where to test the VC. I'll post results soon.

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

LED+ 78.6v down to 55.9v after back lights off.
VC1_13.5v down to 6.0v
VC2_13.1v to 6.0v
VC3_12.1v to 9.3v
VC4_12.9v to 5.7v
VC5_13.0v to 6.0v
VC6_13.0v to 5.9v
Please note that I have no prior experience with testing. Hopefully I had the correct meter setting and test spots this time. I am grateful for everyone who's helping me through this. I tested all of these results twice to make sure they didn't deviate.

[sean0118]

Re: LG 60LB7100 screen goes black seconds after start up

Sounds like your on the right track now, but unfortunately I don't know much about this TV, so you'll have to wait for one of the pros to chime in with instructions.

[dick_barton]

Re: LG 60LB7100 screen goes black seconds after start up

What voltages do you have on the EL test points

[tstew]

Re: LG 60LB7100 screen goes black seconds after start up

I tested all 12 EL from left to right and the first reading is with back lights on the second reading is 15-20sec after back lights off.
EL62-13.1v to,6.1
EL54-12.9v to 6.1
EL55-13.0v to 5.5
EL64-12.9v to 5.3
EL52-12.9v to 5.4
EL66-12.8v to 5.3
EL65-13.0v to 5.3
EL53-12.9v to 5.3
EL63-13.3v to 5.7
EL50-13.2v to 5.7
EL67-12.0v to 8.8
EL51-12.0v to 8.9