Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

[Grasshopper2Ant]

No backlight issue. Have sound and can see menu with flashlight.

Suspect LED driver, voltages are 100V each side. What should the voltages be for 75 inch TV on the Power Supply Board? I have 96 leds x3 volts per=288/2=144 volt per side?
Am I low on my volts causing the leds not to light up?

Before I got all backlights out, the right side was a bit darker than left side. How many leds
need to be out for all to not work?

Thinking of getting a led tester. If leds light up, would that confirm it is the Power Supply Board?

I do not want to dismantle entire board to get at leds at this time and hope to diagnose it is not.the PSB

Thanks for any help guys!.

[diif]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

It's LEDs not driver.

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

Thanks for reply. Anyway to confirm this 100%.

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

No backlight issue. Have sound and can see menu with flashlight.

Suspect LED driver, voltages are 100V each side. What should the voltages be for 75 inch TV on the Power Supply Board? I have 96 leds x3 volts per=288/2=144 volt per side?
Am I low on my volts causing the leds not to light up?

Before I got all backlights out, the right side was a bit darker than left side. How many leds
need to be out for all to not work?

Thinking of getting a led tester. If leds light up, would that confirm it is the Power Supply Board?

I do not want to dismantle entire board to get at leds at this time and hope to diagnose it is not.the PSB

Thanks for any help guys!.

Here is similar board as mine. Can someone tell me how many volts I should be getting at the two LED driver connects on 75 inch Vizio?

Also, I am getting a 300V led tester. If the leds light up on both connects, would that confirm it is power supply board?

Thanks for any help!

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

Power Supply board at LED driver connectors on and off board with power plugged in.

180 plus volts at connectors and board at start-up and dwindles to 100 volts in 5 seconds.

No Vizio logo or backlights.

Is this a normal board booting up?

I am resided to it being backlights but still want to do the 300V LED tester test.

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

Dismantled the TV.
Tested the LEDs with tester. 2 rows consisting of 6 leds each side are out. That is 24 leds out.
Trying to take the reflector sheet off but it is glued to the leds.
How does one deal with the reflector sheet without tearing it. Very poor design by Vizio.
Anyone else have this problem and how did you solve it?

[nomoresonys]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

That sounds pretty odd, post a good picture of this.

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

The led strips are glued to the back as well as the reflector.

I decided to cut the reflector around the leds. Lots of extra bullshit but once I carved out the first one I used it as a template for the rest. Tedious but just get a rhythm going.

A strip with 6 leds measure 34V on my tester.

Ordering a set and update later.

[bscottjohnston]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

Dismantled the TV.
Tested the LEDs with tester. 2 rows consisting of 6 leds each side are out. That is 24 leds out.
Trying to take the reflector sheet off but it is glued to the leds.
How does one deal with the reflector sheet without tearing it. Very poor design by Vizio.
Anyone else have this problem and how did you solve it?

Wondering if a heat gun on low or a hair dryer might get the sheet out without damage. On my 70" Vizio with the panel out the LEDs would start up and I could see which ones were damaged without the tester.

[nomoresonys]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

Could use a hairdryer, not too hot of a setting but most will peel right off with steady slow pulling, did a big vizio the other day, each led had it's own little screw beside it holding the sheet in place, have not seen that very often.

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

Thanks for tips guys!I

I looked at a shop Jimmy video and he cut it out with Olfa razor blade.

That is what I did. 16 strips. Top 4 rows had screws on LED strips, bottom 4 was glued with white thermal tape.

To put back new strips I used double sided thermal tape and on reflector edges and installed.

As a tip, buy or source the tape beforehand. I could not find it anywhere at any

Ordered on Amazon. Cheaper if you have time to get from Aliexpress.

Anyways, all was good till I messed up install which I will start a new thread for help.

[Grasshopper2Ant]

Re: Visio V755-G4 LED TV: No backlight, have sound, see menu with light.

The LEDs I had on my strips were all out on the bad rows, 4 rows.

I replace bad ones with existing good ones and all light up. I did same to other side and all lit up.

I tested a strip and I could not get one individually to light up with my new led tester.

Probably testing it wrong.

[howardc64]

Looks like have one with bad backlight. Here is a diagnostic summary. Will post update after backlight order/replacement and see how easy to get sticky reflector paper off.

Model


Right side backlight failure

This is a white screen test from youtube



LED tester results

Looks like 4x serial circuit. Each circuit is 6 6V LEDs/row x 4 rows or 130V @ 5.4V/LED. A pair of serial circuit is connected in parallel so if only 1 serial circuit fails in this parallel pair causing PSU to safety protection shut off the rail, then both serial circuits will be off. This is exact the pattern on the screen.

LED testor shows 128V on parallel 2x serial circuit for left side of screen and 154V on the right side of screen.



Disassembly Warning

Rear panel switches have a very short connection and connector will break easily. Best to have 2 people can carefully rotate the rear cover off. Here is a photo of my broken one



Misc Pics

[howardc64]

Finally got around to replacing the backlights which is PITA on this model.

• There are 16 strips, 8 rows on each side
• Bottom row is glued to the reflector paper. Need to cut the paper to remove which leaves paper very loose to the frame. Probably best to double side tape down the loose paper (I didn't do)
• Top 4 rows have 2x screw on LED bar besides glued down bar.
• Replacement strips comes in 32 pieces and 2x join together to match 1 OEM strip. This allows shorter package shipping. Need to cut the reflector paper where the joint is to keep reflector paper flat.
• Due to cutting the relfector paper to gain access to the LED strips, backlight evenness deteriorates. Bottom is the worst where cut reflector paper is loosest. See white screen test pic (in person looks slightly better than picture)

On reassembly, really easy to install 2x flex joining 2 buffer boards together upside down (All the printed labels need to face down rather than up) Luckily my prior post picture saved me

[howardc64]

One more note, the left (looking at TV from front) stand mounting bracket has 2 possible positions. Wrong one won't have the indent for the upper stand mounting bolt and will break it. So careful with this on reassembly. I made this mistake.

On the cut reflector paper to extract bottom row of LED strip. The original paper is lifted slightly above the chassis as its glued to the LED strip. When this is cut, there will be a gap (even if the paper is taped down against the tub) and likely cause uneven brightness at the bottom of the screen. Don't know how to avoid this without separating the LED bar from the glued on reflector paper. Furthermore, the plastic stands for the diffuser seem glued onto the reflector paper also so best not to remove the paper.