Toshiba 49L621U

[budm]

Re: Toshiba 49L621U

https://www.analog.com/en/technical-...d-dimming.html

https://focuslcds.com/journals/pwm-d...ight-for-lcds/

"with the unit on pin 15 (dim) is jumping between 3.005v and 3.024v" that is fine.
What is your TV LCD panel model number?

[jostewcrew]

Re: Toshiba 49L621U

It is PWM Dimming control. not variable resistor. You do know what PWM is, correct?

i do not sir...link to good reading? iw ill google it after this message. im assuming by abbreviation pwr managmnt chip?

You should check the dimming DCV reading when backlights stay on, it will be average reading since it is PWM not steady DC.

with the unit on pin 15 (dim) is jumping between 3.005v and 3.024v

BTW, LED tester only puts out about 30 mA instead of 200 ~ 300mA of operating current, so using tester will tell you if you have open circuit or not without having to disassemble the LCD panel, not for verify that the LED is good since bad LED will fail at operating current.

im still familiarizing myself with the tools of the trade. this is good insight on the usage of this device. ive been using it to see only if any voltage reading differs when a circuit of led strips is tested. if they are all lighting and not greater than 3v apart, id say they are good (although sometimes i am unsure of myself so i open up anyway) but if one circuit doesnt light....automatic bulb/circuit failure to me. if one circuit differs between 3v and upwards and the other two are the same...i assume one or more bulbs are out (basing around 3v per bulb)

[budm]

Re: Toshiba 49L621U

It is PWM Dimming control. not variable resistor. You do know what PWM is, correct?
You should check the dimming DCV reading when backlights stay on, it will be average reading since it is PWM not steady DC.
BTW, LED tester only puts out about 30 mA instead of 200 ~ 300mA of operating current, so using tester will tell you if you have open circuit or not without having to disassemble the LCD panel, not for verify that the LED is good since bad LED will fail at operating current.

[jostewcrew]

Re: Toshiba 49L621U

i understand that now with the unit functioning (havnt tested the led dim function as of yet) that some may not want to continue to theorize or such. im learning so im still curious as to why its working now after disconnecting/ reconnecting dim (pin 15)? im assuming its some type of variable resistor ..which i believe would have to be an ic of some sort to be able to increase/ decrease voltage for backlight dimming functionality? budms' insight provided me that it is controlled via the main board...id be interested in figuring out which component that would be and do some testing.

[jostewcrew]

Re: Toshiba 49L621U

How did you confirm the LEDs were good? Backlight flash is usually a sign of bad LEDs. Do you have a LED tester? A few of the Toshibas I worked on had bad LEDs that damaged the LED controller on the power supply. The cost of replacing both was close to the value of the TV.

i first used my backlight tester to test voltages on all 3 strip circuits. they seemed within range of eachother and not off enough to indicate one of the leds went out. i opened it up to visually check each strip after replacing the power board, main board and tcon board without it resolving the issue.

[jostewcrew]

Re: Toshiba 49L621U

to preface: after reconnecting pin 15 (dim) the set still continues to function properly. any reason? reset, something short close or open? did continuity between the wire at connector insert and the backside of the connector adapter itself to verify its actually back installed.

1) So what do you have on DIM pin if all cables are put back in place?
when the unit is off it jumps between 0v and -.1mv

2) What DCV do yo have on the LED connector of EACH pins when you first turn on the TV (you will need to leave the meter probes in place, black probe on chassis, red probe on each LED connector) and then after 10 seconds then turn the TV off, so you have to repeat this test on each pin of the connector that has the wire connected to it, you also need to provide the pin name so we can easily see what it has or does not have..

placed in min/max mode: p803 on power board (connector going to led strips)

with led load:

pin 1 vled1- = 15.6v
pin 2 nc
pin 3 vled2- = 17.1v
pin 4 nc
pin 5 vled3- = 15.3v
pin 6 nc
pin 7 nc
pin 8 nc
pin 9 nc
pin 10 nc
pin 11 vled+ = 97.4v
pin 12 vled+ = 97.1v
pin 13 vled+ = 97.3v

without led load:

pin 1 vled1- = 0v
pin 2 nc
pin 3 vled2- = 0v
pin 4 nc
pin 5 vled3- = 0v
pin 6 nc
pin 7 nc
pin 8 nc
pin 9 nc
pin 10 nc
pin 11 vled+ = 133.9v
pin 12 vled+ = 134.3v
pin 13 vled+ = 131.1v

[neilc6]

Re: Toshiba 49L621U

backlight flash on with toshiba logo, then went black with red led flashing 5 times. leds were good

How did you confirm the LEDs were good? Backlight flash is usually a sign of bad LEDs. Do you have a LED tester? A few of the Toshibas I worked on had bad LEDs that damaged the LED controller on the power supply. The cost of replacing both was close to the value of the TV.

[jostewcrew]

Re: Toshiba 49L621U

sure thing. i will get all of this together and place back all wires. i will post back when ready to begin from the beginning. thank you!

[budm]

Re: Toshiba 49L621U

i hhave a question about this 49l621u model. changed power supply, main board and tcon board to a set that had power, backlight flash on with toshiba logo, then went black with red led flashing 5 times. leds were good and again new pb, mb, and tcon with same issue. also downlaoded and flashed firmware for this model (dont know if it took as it was a black screen) read the posts about blon and dim (pins 13 and 15 respectively) and disconnected the dim from the connector. fired right up.

troubleshooting the power supply and main board connectors at the blon and dim gave 0v both when off, and 3.3v at blon and 2.9v at dim when turned on. being that dim is disconnected from the power supply side of dim, it would be as blon is 3.3v and dim is at 0v.

Question:

is the blon and dim originated from the powersupply board or the main board? if it the main board, is it safe to say that there is some variable resistor or something that dictates dim voltage? if so, in theory, i could replace the resistor ir ic and it wont suck all the voltage from blon turning off the backlights correct? any insight is appreciated.

BL-ON and DIM are controlled by the Main board. BL-ON <1V = OFF, > 2.5V = ON. most TV uses PWM DIM control signal.
1) So what do you have on DIM pin if all cables are put back in place?
2) What DCV do yo have on the LED connector of EACH pins when you first turn on the TV (you will need to leave the meter probes in place, black probe on chassis, red probe on each LED connector) and then after 10 seconds then turn the TV off, so you have to repeat this test on each pin of the connector that has the wire connected to it, you also need to provide the pin name so we can easily see what it has or does not have..
3) We need good clear pictures of the whole back side of the TV showing all the board.
4) We need close up pictures of the LED connector so we can see how many wires it has and which pins the wires are connector too.
5) You must follow instructions as requested.

[jostewcrew]

Re: Toshiba 49L621U

i hhave a question about this 49l621u model. changed power supply, main board and tcon board to a set that had power, backlight flash on with toshiba logo, then went black with red led flashing 5 times. leds were good and again new pb, mb, and tcon with same issue. also downlaoded and flashed firmware for this model (dont know if it took as it was a black screen) read the posts about blon and dim (pins 13 and 15 respectively) and disconnected the dim from the connector. fired right up.

troubleshooting the power supply and main board connectors at the blon and dim gave 0v both when off, and 3.3v at blon and 2.9v at dim when turned on. being that dim is disconnected from the power supply side of dim, it would be as blon is 3.3v and dim is at 0v.

Question:

is the blon and dim originated from the powersupply board or the main board? if it the main board, is it safe to say that there is some variable resistor or something that dictates dim voltage? if so, in theory, i could replace the resistor ir ic and it wont suck all the voltage from blon turning off the backlights correct? any insight is appreciated.

[budm]

Re: Toshiba 49L621U

Show us good clear picture of your C603? Is it missing on your board? What section is it in?

[Nvbenv]

Re: Toshiba 49L621U

Can anyone tell me the volt and UF rating at c603 on the power board. It is a green cap. Please

[nomoresonys]

Re: Toshiba 49L621U

http://tvna.compal-toshiba.com/us/en...=529&model=544 Right there is the download page for 49L621U, instructions should all be there, just be sure to follow them exactly.

[budm]

Re: Toshiba 49L621U

If I were you I would buy a digital meter right now, it will make it much easier to troubleshoot the problems.

[kristapMA]

Re: Toshiba 49L621U

BTW before we get too deep, do you have proper tools to do component level replacement, especially the SMD (surface mounted parts)?

I have basic tools so most likely not. But if it will save me money to fix it myself, I will get the tools i need. My husband did say if something needed to be soldered that we will take it somewhere because he isn't confident that i can do it. I have watched my dad and brothers solder things that I think with instruction I can.

[kristapMA]

Re: Toshiba 49L621U

So did you verify that your meter is OK since you are now basically getting 0V readings?

Pretty sure i had it set wrong... going to take the tv apart today so will double check before i even think about taking the board off but wanted instructions so i have it...

[budm]

Re: Toshiba 49L621U

BTW before we get too deep, do you have proper tools to do component level replacement, especially the SMD (surface mounted parts)?

[budm]

Re: Toshiba 49L621U

I redid the pins and got different numbers. I must be doing something wrong then? I don't get it... my son took a video while I was doing it, maybe someone can tell me what i am doing wrong... I am trying to figure out how to upload the video from my phone and will post when i figure it out.. in the mean time here are the numbers i got...

Standby
1 - 0 - 16v2
2 - 0 - 16v2
3 - 0 - 16v2
4 - 0 - gndp
5 - 0 - gndp
6 -0 - 16va
7 - 0 -gnda
8 - 0 - 16v2
9 - 0 - gndp
10 - .2 (ish) - 5v1 - needle moved a tiny bit
11 - 0 - acd
12 - 0 -pwon
13 - 0 -blon
14 - .2 (ish) - 5v1 - needle moved a tiny bit
15 - .2 (ish) - dim
capacitor - 0v
capacitor - 1v

POWER ON

1 - 1 - 16v2
2 - 1 - 16v2
3 - 1 - 16v2
4 - 0 -gndp
5 - 0 - gndp
6 - 1 - 16va
7 - 0 - gnda
8 - 1 - 16v2
9 - 0 -gndp
10 - 0 - 5v1
11 - .2 ish acd
12 - 0 -pwon
13 - 0 - blon
14 - 0 -5v1
15 - 0 - dim
capicitor - 3v
capicitor - 3v

i can't figure out how to attach the video so I uploaded it to youtube. https://www.youtube.com/watch?v=3jhNrz11i9Q

So did you verify that your meter is OK since you are now basically getting 0V readings?

[budm]

Re: Toshiba 49L621U

Take pictures first so you have the record of how the connectors are in place.
1) Check the Voltage between the two legs of the main filter cap to make sure it is discharged do to 10V or less first.
2) Carefully remove the connectors and then the mounting screws to remove the board.

[kristapMA]

Re: Toshiba 49L621U

I am talking about the bottom soldered side of the board.

ooops sorry i misunderstood.... How do i take it out without damaging anything?