TOSHIBA 32L1400U is dead

[renoid]

Hi guys.

I would like to fix my LCD TV with LED backlight which is completely died, it doesn't turn on and there is no standby light.

I did some tests, and I suspect it is the main board.

I have first checked the Power Supply Board, the fuse is OK, and I think I get correct voltages in the output.

With the main board not connected, I get 0V in the output.

With the main board connected, I get the following voltages in the output:

DIM 3.2V
5V1 5.2V
BLON 0.00V
PWON 3.3V
ACD 3.2V
5V1 5.2V
GND 0.00V
12V2 12.4V
GND 0V
12VA 12.4V
GND 0V
GND 0V
12V2 12.4V
12V2 12.4V
12V2 12.4V

With the mainboard hooked, I connected a resistor across the 5V1 and BLON pins and the backlight turns ON OK.

Pressing the power button does not produce any change in the PWON or any other voltage of the PSU.

I get 170V across the large capacitor.

I don't know if I should test further on the PSU, I think it is working properly.

Regarding the mainboard, I see a little area near the tuner that in the back of the board, is darker, also I see some signs of humidity and oxide.

This is the first time I open and try to fix an LCD TV.

I couldn't find a service manual for this TV.

Any help would be appreciated.

Thanks!

[budm]

Re: TOSHIBA 32L1400U is dead

Its the main board not sending out the BL-ON command to turn on backlights circuit so you need to check the main board at this point. I see two Voltage regulators, U11 is one of the two. Any sign of corrosion should be cleaned off, and inspect the suspected bad parts really well with magnifying glass.

[dskall]

Re: TOSHIBA 32L1400U is dead

Your bottom red circle on your third picture looks like it maybe in the bl-on circuit. Third pin up. I would check that area over real good.

[renoid]

Re: TOSHIBA 32L1400U is dead

Its the main board not sending out the BL-ON command to turn on backlights circuit so you need to check the main board at this point. I see two Voltage regulators, U11 is one of the two. Any sign of corrosion should be cleaned off, and inspect the suspected bad parts really well with magnifying glass.

I checked the two regulators U11 and U14.

U11 is an adjustable regulator G1117.

R1=249ohm , R2=110ohm so Vout=1.802V

I measured:

PIN1=0.55V
PIN2=1.79V
PIN3=4.99V

error% (to 1.8V)= 0.55%
Vout-Vadj=1.24V

U14 is a fixed regulator: 1117-3

It does not have resistors, I measured:

PIN1=0V
PIN2=3.26V
PIN3=4.99V

error% (to 3.3) = 1.21%

Regulators to me are OK.

Your bottom red circle on your third picture looks like it maybe in the bl-on circuit. Third pin up. I would check that area over real good.

I cleaned the board with alcohol and a toothbrush, that seems to have removed the corrosion in that area. I still don't see anything wrong around there but I'll re check.



I have to add: I made it turn on, by connecting a resistor across the 5V1 and PWON. I got image it worked fine. Then I turned it off (by pressing Power button) and the LED indicator remained on, just for a seconds, then it died again, I tried to force it to turn on again but this time it did not work, only get backlight on when I connect the 5V1 to that pin (BLON), I still get the same voltage at the output of PSU.
By the way, what does ACD stand for?

[dskall]

Re: TOSHIBA 32L1400U is dead

ACD stands for A/C detect