LG 47v5500 No Picture No Sound No power to TCON

[MBenesi]

Power board:



Main Board:


Layout:


Checked the voltages from the power board to the main board. All good.

Even with a new main board, there is still no voltage to the TCON board (no voltage across the fuse, which is intact).

Any ideas as to what the problem is?

[budm]

Re: LG 47v5500 No Picture No Sound No power to TCON

If all the Voltages from power board to the main board are OK then do you have backlights? 12V present for sure?

[MBenesi]

Re: LG 47v5500 No Picture No Sound No power to TCON

Thanks for the reply Budm,

No backlights.
Voltages are ~12,~12,~12 ... ~3.5,~3.5 ... ~24, ~3.5 to the main board when power is on.

No voltage across the TCON fuse with power on, which is intact (no resistance).

Umm, should mention that I didn't check the power to the LEDs, and am not exactly sure how to do that (I'm assuming LED+ on either side to the LED strings..). I'll try to check it tomorrow or the next day.

Would lack of LED power cause the main board to not send power to the TCON?

[syaoran123]

Re: LG 47v5500 No Picture No Sound No power to TCON

I assume this is a 47LV5500.

I had a faulty one before, similar symptoms to the way you described it. I replaced the PSU, mainboard and Tcon with good boards from a working 42LV5500 (42 inch and 47 inch models use identical parts). Still the same symptoms.

Trying different combinations, I have confirmed that all pairs of boards were good.

Why the 47inch didnt work when all boards were good remains a mystery. One possibility is the LED backlight has blown and sent an error message to the mainboard. But I already thew away the TV before I thought of that.

PS. voltage across a good fuse will be 0V. quite normal because resistance is 0.

[budm]

Re: LG 47v5500 No Picture No Sound No power to TCON

Thanks for the reply Budm,

No backlights.
Voltages are ~12,~12,~12 ... ~3.5,~3.5 ... ~24, ~3.5 to the main board when power is on.

No voltage across the TCON fuse with power on, which is intact (no resistance).

Umm, should mention that I didn't check the power to the LEDs, and am not exactly sure how to do that (I'm assuming LED+ on either side to the LED strings..). I'll try to check it tomorrow or the next day.

Would lack of LED power cause the main board to not send power to the TCON?

You need to check the DCV between the chassis GND and each end of the T-CON's fuse when TV is ON, not across the fuse terminals.

[bajangerry]

Re: LG 47v5500 No Picture No Sound No power to TCON

Hi, did you get this resolved? I have the same TV with the same problem, I get no 12V at the TCON board measured on the fuse. I can see the 3.5 and 12v (when TV turned on) on the P502 connector on the main board but it does not seem to be sending the power to the TCON board.
I got my hands on some diag/service guides and it seems to indicate that there is a Q507 transistor I need to check but I have not been able to find it yet, need a magnifying glass!