Toshiba 55SL412U

[james28909]

I am at a loss so far with this TV. i have measure with power supply plugged in to wall but disconnected from main, and i get only 5v for standby which is normal i think.
but when i plug the main board back to the power supply, and plug up the power cord, i get readings as if the tv is trying to power on or something without me doing anything.

let me explain it a little further and hopefully we can clear up some of my confusion here. while psu and main connected, when i touch the power button, the voltage on the pin of power button board drops to 0, i can trace this back to the main board, but not on the psu.

what i am trying to decide is, if it is the main board acting up, the power button board, or the psu that is causing this. i have no steady or blinking lights at all and here are my readings

Pin# psu reading with main board disconnected:
16 BLON - 0v
15 DIM - 0v
14 ACD - 0v
13 PWON - 0v
12 5Vcc - 5.0v
11 5Vcc - 5.0v
10 NC
09 12V - 0v
08 12V - 0v
07 GND
06 GND
05 GND
04 24V - 0v
03 24V - 0v
02 GND
01 GND

Pin# psu reading with main board hooked up:
16 BLON - .33v
15 DIM - .01v
14 ACD - 3.3v
13 PWON - 3.05v -> stays at 3.05v even while pressing power button
12 5Vcc - 5.0v
11 5Vcc - 5.0v
10 NC
09 12V - 12v
08 12V - 12v
07 GND
06 GND
05 GND
04 24V - 24v
03 24V - 24v
02 GND
01 GND

i honestly think the main board is the problem here, but would really appreciate if someone could help me or give me some insight.
thanks for reading

[budm]

Re: Toshiba 55SL412U

16 BLON - .33v
15 DIM - .01v

The main board is not sending either the Backlights ON (BL-ON) or the Dimming control for the backlights circuits.
It does send PSON because you do have switched 12V, 24V.

[james28909]

Re: Toshiba 55SL412U

but the thing is, PWON (at psu) stays at 3.05 whether i am pressing the power button or not. when reading the PWON pin on the touch key board, the voltage drops to 0v. i think the main board and touch key board has went south never to return.

the 12v and 24v are like that as soon as i plug main back up and me pressing power button has no effect on it at all. i dont understand why when i press the power button, why does it drop to 0v at touch key board? shouldnt it be the other way around? and main board is not relaying the PWON signal to psu, it is stuck at 3.05v at psu, power button has no effect
EDIT: I am ready to start pulling my hair out haha,
also, i have went ahead and ordered a main board and touch key board.

[budm]

Re: Toshiba 55SL412U

The bottom line is that the main board is not sending out the proper signals, and the PS-ON signal is stuck on even when the Power switch is not activated.

[james28909]

Re: Toshiba 55SL412U

that is exactly what i was thinking and thank you for responding so quickly.

do you know if it is normal, on toshiba's, for the touch key control to read 0v when power button pressed? shouldnt it read something like 3v-3.3v when power button pressed, and 0v when not pressed?

[budm]

Re: Toshiba 55SL412U

It is active LOW signal.

[james28909]

Re: Toshiba 55SL412U

great, so it is normal. i thought something was shorted on the touch key board. anyways, ill replace that to just for extra measure. wasnt but a few bucks anyway and the part from a 46sl412u had matching part numbers. now to wait for this stuff to arrive. ill keep this post updated when i get everything in. thanks for your time budm

[james28909]

Re: Toshiba 55SL412U

hey budm, i have a part number here and was wondering if you could tell me how i can test it. part number is K15A50D
looks like a switching regulator, but i dont think i can test it like a transistor (with emitter, base and collector). this part is beside the bridge rectifier and bolted to the metal heatsink.

it seems a

[budm]

Re: Toshiba 55SL412U

That is Power MOSFET:
http://www.datasheetspdf.com/datasheet/K15A50D.html
http://www.datasheetspdf.com/PDF/K15A50D/705606/1