47LW6500 Debug Help - Power Board or Mainboard?

[dannysporea]

Hi all,

My TV suddenly stopped working and when trying to turn on, just the standby lights come up and the screen does not light. I opened it and tried to debug based on a training manual I found on these boards for a similar TV, but the voltages do not match so I am not sure how to identify the problem. Here is some info:

LG 47LW6500-UA
Power Board: EAX62865401/8 / EAY62169801
Main Board: LA12C / BCM35230 / EAX63969205(0) / EBT61399411

So here is what I did so far:

TEST1
- Removed P502 on the main board
- Jumped pins 1 (PWR_ON) with 9 (3.5V STBY)

- P201 (pins 17, 19 and 21) show 11.94V
- P201 (pins 2, 3 and 4) show 24.05V
- P202 (pins 1 and 12) and P203 (pins 1 and 13) show 35.82V

TEST2
- Removed P502 on the main board
- Jumped pins 1 (PWR_ON) with 9 (3.5V STBY)
- Jumped pins 10 (3.5V STBY) with 18 (DRV_ON)

- P201 (pins 17, 19 and 21) show 12.21V
- P201 (pins 2, 3 and 4) show 23.8V
- P201 (pin 18 DRV_ON) shows 12.21V
- C256+ leg, P202 (pins 1 and 12) and P203 (pins 1 and 13) show 52.9V
- LEDs light up

TEST3
- Removed jumpers and put P502 back on the main board
- Powered the TV on -> LEDs do not light
- P201 (pins 17, 19 and 21) show 11.85V
- P201 (pins 2, 3 and 4) show 24.22V
- P201 (pin 18 DRV_ON) shows 11.85V
- C256+ leg, P202 (pins 1 and 12) and P203 (pins 1 and 13) show 36V
- Attempted to monitor voltage jumps when turning the TV on on C256+ and P202/203, it never goes above 36V

Is this a bad motherboard or a bad power source? Any ideas on what else to test and what next steps to take?

Thanks!

[nomoresonys]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Ok now with everything hooked up try test #3 below, try to do it just as instructed.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Ok now with everything hooked up try test #3 below, try to do it just as instructed.

3) Test connector from mainboard to powerboard on powerboard side with all boards hooked up, test with tv plugged in but off then hit power, report both conditions here, give pin number, pin description/name and condition both off and when you hit power on. So we can see all the voltages and what they are doing.

Should I look for a spike on each pin when hitting power, or just the final reading after power on?

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Ok, here are the values for P201.

Standby

23 - N.C   -> 0V     |  24 - ERROR  -> 0V
21 - 12V   -> 0V     |  22 - PWM   -> 0V       
19 - 12V   -> 0V     |  20 - N.C   -> 0V
17 - 12V   -> 0V     |  18 - DRV-ON  -> 0V
15 - GND   -> 0V     |  16 - VSYNC  -> 0V
13 - GND   -> 0V     |  14 - GND   -> 0V
11 - 3.5V   -> 3.52V   |  12 - 3.5V   -> 3.52V
 9 - 3.5V   -> 3.52V   |  10 - 3.5V   -> 3.52V
 7 - GND   -> 0V     |   8 - GND   -> 0V
 5 - GND   -> 0V     |   6 - GND   -> 0V
 3 - 24V   -> 0V     |   4 - 24V   -> 0V
 1 - PWR-ON  -> 0V     |   2 - 24V   -> 0V

Power

23 - N.C   -> 0V     |  24 - ERROR  -> 0V
21 - 12V   -> 11.84V   |  22 - PWM   -> 3.2V       
19 - 12V   -> 11.84V   |  20 - N.C   -> 0V
17 - 12V   -> 11.84V   |  18 - DRV-ON  -> 0.03V
15 - GND   -> 0V     |  16 - VSYNC  -> 0V
13 - GND   -> 0V     |  14 - GND   -> 0V
11 - 3.5V   -> 3.51V   |  12 - 3.5V   -> 3.51V
 9 - 3.5V   -> 3.51V   |  10 - 3.5V   -> 3.51V
 7 - GND   -> 0V     |  8 - GND   -> 0V
 5 - GND   -> 0V     |  6 - GND   -> 0V
 3 - 24V   -> 24.21V   |  4 - 24V   -> 24.21V
 1 - PWR-ON  -> 3.44V   |  2 - 24V   -> 24.21V

[Andrew F. Ali]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

I have found with the LW series LG LED TVs that the BGA chip becomes disconnected from the Main Bd. Remove the Heatsink and using a Hot air Station and heat the BGA chip for 15 mins at 350 degrees. allow it to cool on its own and refit the Heatsink and give it a try. I have successfully done this accouple times already without any call back complaints.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

I have found with the LW series LG LED TVs that the BGA chip becomes disconnected from the Main Bd. Remove the Heatsink and using a Hot air Station and heat the BGA chip for 15 mins at 350 degrees. allow it to cool on its own and refit the Heatsink and give it a try. I have successfully done this accouple times already without any call back complaints.

Unfortunately I don't have a hot air station, nor did any micro-soldering before... I was planning on trying to find a replacement board once I identify the culprit. Does this look to you that the power board is good and the main board is bad? DRV_ON seems to be very low at 0.03V, so this would support this.

[nomoresonys]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

You are correct sir, the drv_on signal comes from the mainboard when functioning properly.

[viewfindr]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

I have a 55LW6500 that has failed in similar fashion before, and was able to fix it by baking the entire motherboard in the oven (following a suggestion in another thread) as sort of a "low budget" reflow. It worked for a few months the first time before I had to repeat the process again. I think it's worth a try. There's more discussion here.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

I have a 55LW6500 that has failed in similar fashion before, and was able to fix it by baking the entire motherboard in the oven (following a suggestion in another thread) as sort of a "low budget" reflow. It worked for a few months the first time before I had to repeat the process again. I think it's worth a try. There's more discussion here.

If I had an electric oven, I would try it as a last resort, nothing to lose... unfortunately mine is gas. And I still want to try to pinpoint the point of failure on the board if possible. I may be able to solder it back on if it was large enough and not requiring a heat gun or micro soldering.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

You are correct sir, the drv_on signal comes from the mainboard when functioning properly.

Thank you. Any ideas on how to figure out which component is the cause?

[budm]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Are you getting any video on the screen if you use flash lights?
Are you getting 12vdc feeding the T-CON?

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Are you getting any video on the screen if you use flash lights?
Are you getting 12vdc feeding the T-CON?

No video on the screen with flashlights. 0V on the F1 fuse on the T-CON board, as well as P3501 on the mainboard side.

[nomoresonys]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Tcon fuse is good tho correct, just no voltage getting to it?

[Andrew F. Ali]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

These boards are difficult to get unfortunately. However, it is not working properly at the moment, so the option is to heat up the Main Chip. I never tried the baking the board method but I have read on this Forum that it works but temporary though.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

Tcon fuse is good tho correct, just no voltage getting to it?

Yes, no voltage getting to T-CON board at all. Nothing on the mainboard side either, so the cable cannot be blamed.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

So here is what I am seeing on the T-CON's voltage circuit on the main board:

Q505
- B - 0.628V (PANEL_CTL)
- E - 0V (GND)
- C - 0.03V

Q506
- B - 0.03V
- E - 0V (GND)
- C - 12V

Q507
- D - 0V (PANEL_VCC)
- S - 12V (from L511)
- G - 12V

Does this make sense to you? I am not sure what PANEL_CTL value should be, but the D pin on Q507 should be 12V in order to power the T-CON board.

Thank you.

[neilc6]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

PANEL_CTL is likely a logic signal that comes directly from the microprocessor through a BGA connection. Try heating up the processor with a hair dryer before plugging in to confirm you have bad BGA solder balls.

[budm]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

So beside not having DRV drive signal, you also have T-CON power control signal.

Q505
- B - 0.628V (PANEL_CTL) This should change states when you toggle TV on and off, does it?
- E - 0V (GND)
- C - 0.03V

Q507
- D - 0V (PANEL_VCC)
- S - 12V (from L511)
- G - 12V Since this MOSFET is P -Channel, for it to be on, the Gate Voltage has to be at least 3V less than the Source Voltage, this why you get 0V on the Drain pin at this point due to Gate Voltage is at 12V.
So the MICOM is not working correctly at this point.

[dannysporea]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

So beside not having DRV drive signal, you also have T-CON power control signal.

Q505
- B - 0.628V (PANEL_CTL) This should change states when you toggle TV on and off, does it?
- E - 0V (GND)
- C - 0.03V

Q507
- D - 0V (PANEL_VCC)
- S - 12V (from L511)
- G - 12V Since this MOSFET is P -Channel, for it to be on, the Gate Voltage has to be at least 3V less than the Source Voltage, this why you get 0V on the Drain pin at this point due to Gate Voltage is at 12V.
So the MICOM is not working correctly at this point.

PANEL_CTL on the base of Q505 barely changes voltage when toggling TV on and off: 0.6V when off and 0.63V when on.

[budm]

Re: 47LW6500 Debug Help - Power Board or Mainboard?

PANEL_CTL on the base of Q505 barely changes voltage when toggling TV on and off: 0.6V when off and 0.63V when on.

The MICOM is not sending the control signal for this section of the circuit beside the DRV circuit.