LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

[neex]

All voltages to my knowledge check out fine. The set comes on and I am unable to power it off with the power button.. volume control doesn't work and neither do source selections.... I only get fuzz and 'white noise' audio. I didn't know if this was something common - I have searched the forum so I apologize if I missed something... I will be replacing every primary/filter cap but something tells me this isn't the issue as the rails seem to be putting out voltage within/above spec....

Here are my readings from P201 and P202

202
(1)19V - 20.6
(2)19V - 20.6
(3) GND
(4) GND
(5) 6V - 6.09
(7) GND
(8) 3.4V - 3.46
(9) GND
(10) 12V - 12.8
(11) GND

P201
(1) 3.4V (1.94 with connector unplugged and 3.46 with it plugged in)
(2) GND
(3) 6V - 5.96
(4) DIM -
(5) GND
(6) ST/5V - 4.97
(7) I.B. - 1.69
(8) ERR - .013
(9) IC - 4.8
(10) GND
(11) ST/5V - 4.96
(12) ON - 2.69
(13) ACD - 4.21

measuring from one side of the ground plane to the ground screws is pretty consistent at .036V...

Any ideas? I feel like I'm pretty close here....

Thank you,
A.

[dskall]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

I would be checking for voltages at the regulators on main board

[dskall]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

Also check for voltage at cable to the buttons. There should be power there and one or more pins should change voltage when you press different buttons.

[neex]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

I pulled it on the bench again and the original statement about 3.4 changing states was false. The 3.4 ON pin reads 1.8V even when powered with backlights on. I did check the pinout from the power button and it changed voltage from 1.94V. All I can think of now is that a regulator somewhere on the main board is outputting the same or very close. I've also been probing transistors to see if any of them pass along the button press.

I think that once the 3.4V rail is sorted out this should be fixed. Time to check the backside of the main board I guess....

P1300 shows 3.3 high to 2.17 at KEY2 when power button is pressed. The very first cap to the right of the circuit tests as open. I hope I'm getting close... now to find a 8b 47 25J compatible cap in by parts bin....

How do I interpret this capacitor? I found B to mean +/- 0.1pF and I can guess the 25 represents voltage? Is this a 470uf @ 25V cap? Anyone??

Thanks!

[neex]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

Does 47nF sound right? @5% Tolerance? Not sure of the voltage though... guess I'll aim high...

[neex]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

nevermind - figured out the cap after testing a good one out of circuit... only problem left is no RL ON being sent from mainboard... I think I checked every regulator but might have missed one... getting very close....

[dskall]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

If your getting voltage changes from key press you may have an eeprom problem.

[neex]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

that would be more interesting than I bargained for.... the key presses don't manifest any voltage fluctuation at the SMPS however.... only on the lower section of the main board by KEY2 outputs...

[dskall]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

Key presses go through the main processor.

[neex]

Re: LG 37LC5DC - 'snow' for video/audio but no control of buttons/menu/etc...

maybe I'll get a scope on the outputs on the processor then... thanks.