Toshiba 50L1350UC not powering on

[DasBub]

Hi folks.

I have a Toshiba 50L1350UC which almost never powers on. This situation started with it occasionally not powering on, then progressively got worse until the owner (my aunt) decided to just leave it on 24/7. Whenever she accidentally powered it off, she would continuously cycle its power bar and press the Power button again and again until it turned on. Eventually she gave up and it moved to my house.

I've already checked the standby voltage, and it's a solid 5.1V, as labeled on the board. I tried to check the bridge rectifier's output but I got a spark and a loud pop as soon as I put the red lead near the positive leg of the rectifier. Maybe I got too close to another component.

Strangely enough, the TV started working after the sparking! I could turn it on and turn it off and turn it on again about 20 times and it worked 100%! Then I unplugged it for about ten minutes and tried again, but it stopped working.

I've attached some snaps from my phone. Let me know if you need close-ups and/or part numbers.

Any help is appreciated!

[DasBub]

Re: Toshiba 50L1350UC not powering on

Anybody?

[budm]

Re: Toshiba 50L1350UC not powering on

https://www.badcaps.net/forum/attach...5&d=1483325647
That white connector of the power supply board that goes to the main board has labels for each pin of the connectors, we need the pin name follows by the DCV readings so we can see what are missing for each pin.
BTW, pictures are not in focus.

[DasBub]

Re: Toshiba 50L1350UC not powering on

Okay, the values are thus:

PWM: 0V
5.1V: 5.1V
BL_On/Off: 0V
Power_TV: 0V
AC Detect: 0V
5.1V: 5.1V
GND: 0V
12V_LNB: 0V
GND: 0V
12V_AUD: 0V
GND: 0V
GND: 0V
12Vcc: 0V
12Vcc: 0V
12Vcc: 0V

I've included some (hopefully) better pictures.

Thanks for your help.

[budm]

Re: Toshiba 50L1350UC not powering on

OK, I believe the AC Det should normally be around 3VDC if the incoming AC detect is OK, I will need to look at my old notes to verify, this may have cause the main board to be locked from sending the PS-ON (POWER ON) signal to turn on the rest of the power supply.

[DasBub]

Re: Toshiba 50L1350UC not powering on

What could cause the AC Det to fail? Does it just detect whether or not AC is present or whether it is at the proper voltage and frequency?

[budm]

Re: Toshiba 50L1350UC not powering on

The AC detect is part of the protection circuit in case the incoming AC is not within the TV operating range.
Topical failure are due to bad resistors, bad OPTO. I did not have the time to look up the info for this model yet.
Most Toshiba TV, 3VDC = Good AC Det, <1V = Bad AC DET.
http://www.shopjimmy.com/catalogsear...oshiba+50L1350

Toshiba 75033153 (PK101W0050I, FSP156-3FS01) Power Supply Unit
http://www.shopjimmy.com/toshiba-750...upply-unit.htm

[DasBub]

Re: Toshiba 50L1350UC not powering on

Cool. Thanks for the info. I'll check the resistors and read up on checking optos (never done that before).

[nickmatine1]

Re: Toshiba 50L1350UC not powering on

so, finally did you changed tjhe power supply?

[DasBub]

Re: Toshiba 50L1350UC not powering on

I ended up swapping the power supply board for a working one, probably pulled from another unit.

The new power supply lasted about six months before croaking.