Toshiba 58L4300U no leds

[freelancenoob]

First of all I am no expert when it comes to electronics. So please if its something small and stupid that could have been over looked, dont bash me for it. lol Teach me instead.

Ok I just picked up this tv last night. Owner said it has sound but no picture. I got it home and plugged it in and the Toshiba logo lite up for about 2 seconds or so and then went away. I hooked up the dvd player to hdmi 1 and it started playing sound. If I turn the tv off and back on the Toshiba logo does not appear. If I unplug for a moment and plug it back in the Toshiba logo comes back.

I have included photos of the power supply. If there is anything you want to see a closeup of let me know. I have also included a video. I don't do videos very well so dont judge me lol.

https://youtu.be/RQCxnoErqHk

[dick_barton]

Re: Toshiba 58L4300U no leds

Can you measure the voltage on each pin of P803 at switch on.

Photo's courtesy of Shopjimmy

[freelancenoob]

Re: Toshiba 58L4300U no leds

Lb1+ 120
lb2+ 120
lb3+ 120
lb4+ 120
lb5+ 120
n.c.
N.c.
Lb1- 14.8
lb2- 14.8
lb3- 0
lb4- 14.8
lb5- 14.8

I checked and rechecked LB3-. Checked ground and tested again. Same results. These are all voltages with power on.

can you measure the voltage on each pin of p803 at switch on.

Photo's courtesy of shopjimmy

[dick_barton]

Re: Toshiba 58L4300U no leds

It looks like you have no return on led string LB3. Using your meter set to diode mode compare Q308 to the others alongside it. However it is possible that you have an open circuit led in string LB3

[freelancenoob]

Re: Toshiba 58L4300U no leds

It looks like you have no return on led string LB3. Using your meter set to diode mode compare Q308 to the others alongside it. However it is possible that you have an open circuit led in string LB3

Forgive me on this. Im assuming you want me to put it in continuity mode correct but where is Q308

[budm]

Re: Toshiba 58L4300U no leds

Looks like open circuit in the LED #3, LB3- is the Cathode return pin of the LB3 LED string.

[dick_barton]

Re: Toshiba 58L4300U no leds

Forgive me on this. Im assuming you want me to put it in continuity mode correct but where is Q308

I posted pictures of front and back of the power supply board. It's located on the back of the board. Set the meter to diode test with set off and compare to the other mosfets alongside.

[freelancenoob]

Re: Toshiba 58L4300U no leds

I posted pictures of front and back of the power supply board. It's located on the back of the board. Set the meter to diode test with set off and compare to the other mosfets alongside.

I see why I was confused now. My board it is labeled differently. But I checked the post from long leg to long leg and each one would start at around 1730 and jump to 1940 before cutting out to 1. All had the same readings.

[dick_barton]

Re: Toshiba 58L4300U no leds

If you feel confident then using a pin you should be able to push the little tab on the connector where LB3- is located and lift it out of the connector. (That is the connector that plugs into the power supply board.) Swap its position with, say LB1- .
If LB1- now shows 0V then string 3 definitely has an open circuit led.

[freelancenoob]

Re: Toshiba 58L4300U no leds

If you feel confident then using a pin you should be able to push the little tab on the connector where LB3- is located and lift it out of the connector. (That is the connector that plugs into the power supply board.) Swap its position with, say LB1- .
If LB1- now shows 0V then string 3 definitely has an open circuit led.

Ok swapped pins on wireharness from LB3 to LB2 and vis versa. LB2 now reads 0 and LB3 reads 14.6.

[budm]

Re: Toshiba 58L4300U no leds

Bad L3 LED string.

[dick_barton]

Re: Toshiba 58L4300U no leds

As Budm says, you have a bad led string L3.

[freelancenoob]

Re: Toshiba 58L4300U no leds

I pulled the wire from the plug and did a continuity test and it is in fact going to the center led strand. Did that just incase they didnt put them in order. lol

[freelancenoob]

Re: Toshiba 58L4300U no leds

Thank you all for teaching me how to diagnose if it was led's or not. Learn something new everyday. I got this tv for free so a little work to get it going doesn't bother me none. Picking up a 65" vizio tonight. Owner said it has 2 black lines on it. Don't know if vertical or horizontal. Owner was going to trash it this weekend. But its another freebie.

[budm]

Re: Toshiba 58L4300U no leds

You may find some bad LEDs but you should also inspect the SMD connectors really really well, you may want to re-solder them all or use jumper wires. Those connectors are not well designed and mouted without much mechanical supports.
https://www.badcaps.net/forum/showth...124#post690124

Hopefully it is just bad connectors:
https://www.badcaps.net/forum/showthread.php?t=65097

[freelancenoob]

Re: Toshiba 58L4300U no leds

I was watching a video the other day on testing led's. The video I watched they scraped a tiny spot of paint off the strip on each side of the led. voltmeter in continuity has just enough voltage to dimly light the led. if it lights then its good.

[budm]

Re: Toshiba 58L4300U no leds

FYI: Some meter in DIODE or Continuity mode may not put out enough Voltage to bias on the LED.

[dick_barton]

Re: Toshiba 58L4300U no leds

So have you found a dead led or poor connection going to the led strip (L3) or the interconnection of the two halves?

[freelancenoob]

Re: Toshiba 58L4300U no leds

So have you found a dead led or poor connection going to the led strip (L3) or the interconnection of the two halves?

I did a continuity test from the wire in the hardness to the test port on the led strip at the beginning of the middle strand. Its the only test port on any of the strands that would come back as the same.

[freelancenoob]

Re: Toshiba 58L4300U no leds

FYI: Some meter in DIODE or Continuity mode may not put out enough Voltage to bias on the LED.

You are correct. Mine however does not. I have an old atx power supply sitting around i've been wanting to convert to a bench power supply. That would probably be better for testing with.