Toshiba 55LF621U21

[Dellinger316]

Hello,
Does anyone have the schematic for this set or the Power Supply 1T920000900. Thank you

[nomoresonys]

Re: Toshiba 55LF621U21

Do you want to tell us your symptoms.

[Dellinger316]

Re: Toshiba 55LF621U21

Hi,
The symptoms are the set does not come on. The red set indicator lights and appears to respond to remote inputs but that's all. I cannot determine if there is sound as I do not know what is any indication there is. I have measured 2x12v 1x3v 2x18v but nothing on the led connector. I do not even know how much potential to expect there. If I bad a schema, I could hunt for some missing electrons. Thank you

[nomoresonys]

Re: Toshiba 55LF621U21

The first thing I try is a simple reset, unplug tv for 5 minutes, hold the power button in on the tv for 30 seconds if it has buttons then plug it back in and try it.

[nomoresonys]

Re: Toshiba 55LF621U21

Monitor, meaning check pin5 PW ON and pin16 BL ON, in standby, leave probe where it is and hit power button, report both readings, example PW ON-standby 0 volts, push power on button and it goes to 3.3 volts.

[R_J]

Re: Toshiba 55LF621U21

The backlight voltage will be around 120~130vdc, you need to check the voltage across P803, pins 1 and 5 when you first turn on the tv as the voltage will drop if there is a fault detected, likely an open led in the panel.
You should be able to check the raw dc voltage for the led circuit across C901 or C902 (Top side from J201 to D902 cathode), the boosted voltage will be across C904 and C905 but only if the circuit is not in protection.

[Dellinger316]

Re: Toshiba 55LF621U21

First off, thanks for the great advice. Reset did not work. Plug tv in no buttons pressed led+ is 90V. 12v1=9.1 pwon=0v 18va=14.6 blon did not measure, When the pwr button on remote is pressed, 12v1 goes to 12 pwon goes to 3.1 18va goes to 18 and led+ goes to 170v. The reason I did not see was blon was doing, was an accessibility issue. I was not sure where to monitor a pin I coild not get to. Thank you

[EazyBone]

Re: Toshiba 55LF621U21

Take a flashlight to the screen after you turn it on. Use strongest one you have and move it at angles on the screen and look for a image. Try hitting the settings button on remote also to pull that menu up and look for the menu. If you have a faint image on the screen. It's probably a backlight issue. Possible to be power board, but these cheap TVs the lights go out all the time.

[nomoresonys]

Re: Toshiba 55LF621U21

First off, thanks for the great advice. Reset did not work. Plug tv in no buttons pressed led+ is 90V. 12v1=9.1 pwon=0v 18va=14.6 blon did not measure, When the pwr button on remote is pressed, 12v1 goes to 12 pwon goes to 3.1 18va goes to 18 and led+ goes to 170v. The reason I did not see was blon was doing, was an accessibility issue. I was not sure where to monitor a pin I coild not get to. Thank you

The bottom ones are tougher to get to, I usually carefully insert a stripped bread tie to take the measurements.

[Dellinger316]

Re: Toshiba 55LF621U21

I will try to monitor BLON. But, if +VLED is toggling, does that not mean BLON is doing something? What indication should I look for on BLON? Is the +VLED going for 90V to 170V normal or is it confirming an issue with the leds not dropping any voltage? Thank you.

[nomoresonys]

Re: Toshiba 55LF621U21

RJ said 120-130 so yes looks like a backlight problem.

[Dellinger316]

Re: Toshiba 55LF621U21

So, as it turns out- J205 is BLON. 0V at plug in no buttons pressed. When the power button is pressed, it is 2.99 then red light goes out. When the red light is on BLON is 0V. Sometimes at power on the red light will blink about 12 times then go out.

[nomoresonys]

Re: Toshiba 55LF621U21

Ok, so looks like the mainboard does send the bl-on signal, so probably it senses the backlight error and shuts down for safety, I would take a good close look at the backlights, prolly at least one is bad, possibly a bad connection in backlight circuit but more likely bad led/s. Have to be very careful taking panel off if it cracks or breaks game over, check some youtube videos for procedure, they are easy to break, need to be in a very patient mood and take it slowly, we're here to help if you have any questions.

[nomoresonys]

Re: Toshiba 55LF621U21

Here's our friends doing a backlight replacement: https://www.youtube.com/watch?v=I51vKi8MyvY

[Dellinger316]

Re: Toshiba 55LF621U21

Thank you so much for all the help. The video was a nice touch. Thanks

[EazyBone]

Re: Toshiba 55LF621U21

I have the 50 inch version of this right now. Did you ever take a flashlight to the screen as I said? Worked for me and shows picture

[nomoresonys]

Re: Toshiba 55LF621U21

Agree, flashlight test is very good, on lots of tvs, including this one as EasyBone confirms, it lets you know that it's just a backlight issue if you see a good image, it won't be bright of course.

[Dellinger316]

Re: Toshiba 55LF621U21

I was not able to see anything. But thought I did. LOL

[nomoresonys]

Re: Toshiba 55LF621U21

It can be very hard to see anything, try the flashlight test while hitting menu.

[Dellinger316]

Re: Toshiba 55LF621U21

Hello all,
Tried the flashlight thing and it is showing info on the screen! I am so excited. I just wish I had a service manual to order the LED's and have them ready when I try to take this thing apart. I know how delicate they are. To bad they don't make the sets where the LED is like changing a light bulb. You know, like slide the strip out the side of the TV, Slide the new one in and connect and GO!!