Vizio V755-J04 no backlight

[Lee M.]

When set is plugged in the BL will flash on for 1/2 sec and show the Vizio logo. I can shine a flashlight on the screen and still see the logo. Checking voltages on the PS/BL driver board look good on the connector to the main board with 5V on pin 15 (BL on/off). The voltage on the two BL connectors jump to around 90V for 1/2 sec when the AC power cord is plugged in then drop to .6V. I tried it with BL's connected and with BL's disconnected and the voltage was the same, jump to around 90V and then drop to around .6V. If the PS/BL driver board is good shouldn't the voltage stay up around 90V and not drop like this board is doing? thanks, Lee

[nomoresonys]

Re: Vizio V755-J04 no backlight

need good pictures of each board and one of the whole back as to see how everything is connected.

[diif]

Re: Vizio V755-J04 no backlight

The voltage drops as it's detecting a problem with the LEDs or wiring, probably the LEDs.

[Lee M.]

Re: Vizio V755-J04 no backlight

If there is one or more shorted LED's the amp draw would be high and the protection circuit would shut down the BL's. But if I disconnect the BL's so there is no load it does the same exact thing, 90V for 1/2 sec and then nothing. It seems like I remember testing other BL driver boards and when I disconnected the BL's the voltage on the connector pins would stay up and not drop to zero with no load like this one is doing. That is how I knew the BL's were bad and not the driver board. Since this one is acting the same regardless if the BL's are connected or not has me wondering if the driver board might be bad?

[Lee M.]

Re: Vizio V755-J04 no backlight

vizio e650i-a2 backlight flashes then turns off
vizio e650i-a2 (LWJAOZBP Serial) led backlight flashes then turns off, has video (via flashlight) and audio.

panel: au optronics T650HVN05.4
72 led total on 12 strips, 6 led per strip wired in three groups of 24 (led driver board has three anode and three cathode pins)
link to datasheet: https://datasheetspdf.com/pdf-file/8.../T650HVN05.4/1

Vizio 56.04219.641G (liteon PA-3231-01WN-LF) Power Supply Unit
https://www.shopjimmy.com/vizio-56-0...-power-supply/

Vizio 55.75J01.001G (91.75J10.004G) Main Board
https://www.shopjimmy.com/vizio-55-7...-for-e650i-a2/

Vizio 55.65T07.C07 (T650HVJ02.0, 65T09-C00) T-Con Board
https://www.shopjimmy.com/vizio-55-6...oard-e650i-a2/

Vizio 55.64S03.DE0 (4H+V3516.001/D) LED Driver Board
https://www.shopjimmy.com/vizio-55-6...-for-e650i-a2/

Vizio T650HVN05.4 LED Backlight Strips
vizio ep-65t01e01-jaa4x 65" led light bar
https://www.shopjimmy.com/vizio-t650...ght-strips-12/

voltages with tv off and plugged in:
====================================
Power Supply
cn203 (12 pins)
pins 1-5 (vddb)= 0v
pins 6-10 (blgnd)
pins 11-12= N/C

cn202 (14 pins)
pins 1-5 (vddb)= 0v
pins 6-10 (blgnd)
pin 11 (lamp_det)= 0v
pin 12 (vblon)= 0v
pin 13= N/C
pin 14 (dim)= 0v

cn201 (4 pins)
pins 1-2 (24v)= 0v
pins 3-4 (gnd is marked on board, but pin 3 is N/C)

cn101 (15 pins)
pins 1-2 (5vsb marked on board, but pin 2 is N/C)= 5.04v
pin 3 (ac_off_det)= .655v
pin 4 (ps_on)= 66mv
pins 5-6 (gnd)
pins 7-8 (5vres marked on board, but no pins connected)
pins 9-10 (gnd marked on board, but pin 10 is N/C)
pins 11-12 (reg_12v)= 0v
pin 13 (vblon)= 0v
pin 14 (dim)= 0v
pin 15 (lamp_det marked on board, but pin is N/C)

led driver board:
cn1 (14 pins)
pins 1-5 (vddb)= 0v
pins 6-10 (blgnd)
pin 11 (det)= 0v
pin 12 (vblon)= 0v
pin 13 (N/C)
pin 14 (e_pwm)= 0v

cn2 (12 pins)
pins 1-5 (vddb)= 0v
pins 6-10 (blgnd)
pins 11-12 (N/C)

cn3 (12 pins to led strips, only uses six wires)
pin 1 (1anode)= 0v
pins 2-3 (N/C)
pin 4 (2cathode)= didn't measure this pin
pin 5 (3anode)= 0v
pins 6-7 (N/C)
pin 8 (4cathode)= didn't measure this pin
pin 9 (5anode)= 0v
pin 10-11 (N/C)
pin 12 (6cathode)= didn't measure this pin
================================================== ======

voltages with tv on:
====================
Power Supply
cn203 (12 pins)
pins 1-5 (vddb)= 24.68v
pins 6-10 (blgnd)
pins 11-12= N/C

cn202 (14 pins)
pins 1-5 (vddb)= 24.70v
pins 6-10 (blgnd)
pin 11 (lamp_det)= 0v
pin 12 (vblon)= 3.3v
pin 13= N/C
pin 14 (dim)= 2.278v

cn201 (4 pins)
pins 1-2 (24v)= 24.70v
pins 3-4 (gnd is marked on board, but pin 3 is N/C)

cn101 (15 pins)
pins 1-2 (5vsb marked on board, but pin 2 is N/C)= 5.03v
pin 3 (ac_off_det)= .649v
pin 4 (ps_on)= 2.368v
pins 5-6 (gnd)
pins 7-8 (5vres marked on board, but no pins connected)
pins 9-10 (gnd marked on board, but pin 10 is N/C)
pins 11-12 (reg_12v)= 11.82v
pin 13 (vblon)= 3.3v
pin 14 (dim)= 2.278v
pin 15 (lamp_det marked on board, but pin is N/C)

led driver board:
cn1 (14 pins)
pins 1-5 (vddb)= 24.69v
pins 6-10 (blgnd)
pin 11 (det)= 0v
pin 12 (vblon)= 3.3v
pin 13 (N/C)
pin 14 (e_pwm)= 2.278v

cn2 (12 pins)
pins 1-5 (vddb)= 24.69v
pins 6-10 (blgnd)
pins 11-12 (N/C)

cn3 (12 pins to led strips, only uses six wires)
pin 1 (1anode)= 24.41v
pins 2-3 (N/C)
pin 4 (2cathode)= didn't measure this pin
pin 5 (3anode)= 24.41v
pins 6-7 (N/C)
pin 8 (4cathode)= didn't measure this pin
pin 9 (5anode)= 24.41v
pin 10-11 (N/C)
pin 12 (6cathode)= didn't measure this pin
================================================== ========

what i have done so far:

only problem i could find on original led driver board was that pin 5 (3anode) did not have any voltage on it.
fuse f2 was blown.

disassemble panel and check each individual led strip (12 of them) using a hp laptop psu with output of 19.28 volts.
all led on each string lit completely.

bought this kit from shopjimmy:
https://www.shopjimmy.com/vizio-e650...air-parts-kit/

fed a full 3.3v to ps_on (with wire to main disconnected, of course) because i thought 2.368v might be too low
(made no difference).

so, long story long ;-) tv acts same as original boards. power comes on and backlight flashes once, then turns off.
flashlight shows image (says "no signal" after displaying vizio logo) and have audio, but nada from backlights.
initial voltage on led driver board cn3 (pins 1,5,and 9) is 84v then dropping and holding at 24v.

the only signal i see that might be a problem is the DET signal, but i don't know. i'm a noob on these led backlit
tv's, so i would appreciate some help from the Wise Ones here on the forum. Thanks! James

[Lee M.]

Re: Vizio V755-J04 no backlight

The post above is another Vizio with the same symptoms as mine. He checked the BL led's and they were all good. "disassemble panel and check each individual led strip (12 of them) using a hp laptop psu with output of 19.28 volts.
all led on each string lit completely." So I'm assuming the problem was with the driver board, but the OP never posted what the fix turned out to be.

[diif]

Re: Vizio V755-J04 no backlight

If there is one or more shorted LED's the amp draw would be high and the protection circuit would shut down the BL's. But if I disconnect the BL's so there is no load it does the same exact thing, 90V for 1/2 sec and then nothing. It seems like I remember testing other BL driver boards and when I disconnected the BL's the voltage on the connector pins would stay up and not drop to zero with no load like this one is doing. That is how I knew the BL's were bad and not the driver board. Since this one is acting the same regardless if the BL's are connected or not has me wondering if the driver board might be bad?

You're aware LEDs can fail open too ?

[Lee M.]

Re: Vizio V755-J04 no backlight

Right I know led's can fail open, but I have not seen a TV with a protection circuit that turns off the voltage due to an open circuit. The few sets I've worked on still had voltage on the BL pins with the BL's disconnected. Since this is a 75" TV I was hoping to avoid taking the panel apart risking breaking it only to find all the led's are good like the poster above did with another Vizio.

[dskall]

Re: Vizio V755-J04 no backlight

That's why they only go to a certain voltage and then shut down. Also, lighting 12 leds with 19v is not a proper check. In fact, most backlight testers can't load leds like the tv does.

[nomoresonys]

Re: Vizio V755-J04 no backlight

from what I can tell, the only problem I see with your voltages is the ac-det, which should probably be about 3.3 volts.

[nomoresonys]

Re: Vizio V755-J04 no backlight

no ac det usually means a problem with power board.

[Storyteller12]

Re: Vizio V755-J04 no backlight

Please post pictures of the boards. Second post asked but you never uploaded them.

[Lee M.]

Re: Vizio V755-J04 no backlight

Here's some pics, sorry for the delay.

[dskall]

Re: Vizio V755-J04 no backlight

Replace your backlights.

[nomoresonys]

Re: Vizio V755-J04 no backlight

Right I know led's can fail open, but I have not seen a TV with a protection circuit that turns off the voltage due to an open circuit. The few sets I've worked on still had voltage on the BL pins with the BL's disconnected. Since this is a 75" TV I was hoping to avoid taking the panel apart risking breaking it only to find all the led's are good like the poster above did with another Vizio.

get a backlight tester, they're not perfect but they are very useful to get a clue of whats going on, around 20 bucks on amazon, a small price to pay compared to a broken screen or the total teardown required for most backlight replacement jobs, which has to be done anyway if that is the problem.

[nomoresonys]

Re: Vizio V755-J04 no backlight

Ideally you want one that gives both voltage and current readings, example there: https://www.amazon.com/HELYZQ-0-320V...3D%3D&sr=8-162

[nomoresonys]

Re: Vizio V755-J04 no backlight

notice that one goes to 320 volts, some of the others only go to 230 or so.

[diif]

Re: Vizio V755-J04 no backlight

Maximum current is only 35mA with that tester, that's more of a gentle tickle.

One that tests up to 150mA https://www.aliexpress.com/item/1005002498419259.html

[nomoresonys]

Re: Vizio V755-J04 no backlight

its all about how much you want to spend, I doubt the op wants to go into the tv repair business or I would have suggested something better than both of those and I doubt he would want to wait 2 to 6 weeks to get it.

[diif]

Re: Vizio V755-J04 no backlight

Which one do you recommend that's better than both