Vizio E470i-A0, No power, suspect bad LEDs?

Question

Vizio Television

Repair guides and support for LED, LCD, HD and other Vizio TVs.

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Justin Castle @erelectronics

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Eagle River Electronics

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crwdns2931729:0crwdne2931729:0: Maw 29, 2024

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Vizio E470i-A0, No power, suspect bad LEDs?

Vizio E470i-A0 with no power.

TV brought in for diagnosis and quote for repair. As usual, I am never confident with my diagnosis on TVs.

TL;DR: Power board throws stable voltages to the main board that I think are all correct. On the LED side it throws less stable voltage and returns ~50% power on LED1 but only ~25% power on LED2.

I think what I have found indicates bad LEDs, but not sure.

When trying to turn on, the TV displays no image. The LED power indicator lights up for a few seconds and then slowly fades to black. Flashlight test does not reveal any image hidden in the black screen. TV makes no noise of any kind from the speakers.

I first suspected faulty power board.

There is 1 fuse and it is not blown. No popped caps or any other failed components on the power board that I can find. AC power comes into the board just fine. On the DC side, there is some stable voltages (Main Board side) and some less stable (LED side).

Testing the power board pinout to main board:

1: 5.1V - Good (5.2V at all times)
2: 5.1V - Good (5.2V at all times)
3: Ground - Good (continuity)
4: Ground - Good (continuity)
5: Ground - Good (continuity)
6: 12V - Good (11.97V when TV "on") 11.97 3.27 3.21 3.06 3.06
7: 12V - Good (11.97V when TV "on")
8: PS On/Off - Good? (3.27V when TV "on")
9: Blu On/Off - Good? (3.21V when TV "on")
10: PWM1 - Good? (3.06V when TV "on", 1.01V when TV "off")
11: PWM2 - Good? (3.06V when TV "on", 1.01V when TV "off")
12: N.C. - Good (no contact)

Testing the power board pinout to the LEDs:

1: LED1 - Bad? (~60V-70V, unstable/fluctuating, when TV "on")
2: N.C. - Good (no contact)
3: VOut1 - Bad? (~120V-130V, unstable/fluctuating, when TV "on")
4: N.C. - Good (no contact)
5: LED2 - Bad? (~30V-40V, unstable/fluctuating, when TV "on")
6: N.C. - Good (no contact)
7: VOut2 - Bad? (~120V-130V, unstable/fluctuating, when TV "on")

(In all cases above, "when TV 'on'" means after plugging it in and after hitting the power button. If "off" is not specifically identified, it is effectively 0V when off.)

On both sides, if I have hit the power button, regardless of the little power indicator LED's current status as lit or not, the power remains. Any time after doing that, the power stays active (stable on the Main Board side, less so on the LED side) until the TV is unplugged. Pressing the power button again doesn't change the power flow. Holding the power button for approximately 6 seconds will reset the power to 0V but it will immediately rise back to the indicated levels above, if the power button is hit again, not hit again, or continued to be held.

I believe these readings are indicating to me bad/failed/burnt out LEDs, but I am not sure. It seems every time I think I have a TV figured out, the next one is different.

Hoping some of the expert here who know TVs better than me can chime in if I'm on the right track or have gone way off course.

Thank you for your time and any help!

EDIT: My LED tester:

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jayeff @jayeff

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crwdns2931729:0crwdne2931729:0: Maw 29, 2024

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Hi @erelectronics

If you're going to get into LED TV repairs, invest in a TV backlight tester (examples only)

They're a quick way to know if the backlights are all OK or not.

Just unplug the backlight power cable from the power board and connect the tester to each LED circuit on the cable plug. It supplies the power for the LEDs and not the power board. If they work it's the power board (or perhaps the mainboard), if they don't it's the LED strip.

Interesting to see that there's a power board LED repair kit available (scroll down to find), so perhaps it's a known problem with the power board.

Cheers

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Hi Jayeff, and thanks for your response.

I actually already have a dedicated LED tester. Photo amended to original post for your consideration.

The instructions that came with it explicitly said not to use it in the way you describe. (I think the wording was "Never test any LED strips while they are still connected", or something to that effect.)

For the record, it does work. I have used it successfully many times to identify faulty individual strips or LEDs for repair purposes. Just never when those strips were plugged into anything.

So is it that I can safely use it through the connector when the strip(s) is still plugged in? Or is that a function of some testers and not of others? It would be great to not have to fully disassemble a TV every time I want to test the strips and I wouldn't mind buying a different LED tester if that is a possibility only with another one.

Thank you for your time.

crwdns2934271:0Maw 30, 2024crwdnd2934271:0 Justin Castle crwdne2934271:0

@erelectronics

My understanding is that the LED strips (or rather the LED power supply cable at the power board) have to be disconnected from the power board, otherwise it would be trying to supply power both ways i.e. to the strips and back into the board.

You should be able to connect it between the LED+ lead and the return lead on the cable plug going to the LEDs for each strip (or feed if there's more than 1 strip per feed), so you should only have to remove the back cover to do this.

crwdns2934271:0Maw 30, 2024crwdnd2934271:0 jayeff crwdne2934271:0

@jayeff Okay. I have tried that and was able to power and get light from line LED1/VOut1 and tried the same but was unable to get any light from line LED2/VOut2.

I think this confirms the LEDs have gone out? At least, one or more of them on line 2?

Thank you for the advice. I genuinely didn't know I could use the tester in such a way.

crwdns2934271:0Maw 31, 2024crwdnd2934271:0 Justin Castle crwdne2934271:0

@erelectronics

The LEDs in a strip (and strips on the same feed) are in a series connection so it only takes one to fail open circuit and the whole strip doesn't light up.

You could try replacing just the individual faulty LED on the strip but getting one that has the same characteristics as the others may not be easy, so you may notice a brightness difference in that area of the screen, when it's working again. Also the others have aged so again might be problematic. Best to get a complete compatible strip or maybe replace all the strips given that one LED (or more) has failed. The probability is that the others may not be far behind anyway.

Looking at the parts link above for the repair kit, there are 12 LED strips in the TV (6 strips/power feed?) and the part number is LC470DUE-SFR1 LC470DUG-JFR1 (examples only to show cost of set of 12).

Usually the part number is printed on the strip itself, if you wish to confirm.

crwdns2934271:0Maw 31, 2024crwdnd2934271:0 jayeff crwdne2934271:0

Hi @erelectronics

Ran out of characters (1024) in my comment above but your LED tester supplies from 0-320V so it can be used to test individual LEDs on a strip, individual LED strips i.e. multiple LEDs in series on a strip, (both of the former are when access to the strips themselves has been achieved - screen assembly disassembled) and complete LED "feeds" i.e. multiple LED strips in series from the power board (TV back cover only removed) as usually individual LED power "feeds" e.g. in your case 2 feeds, will not exceed 320V DC anyway

Here's a video that shows how to replace the strips in the TV.

Apologies if you knew how to do this already.

crwdns2934271:0Mha 1, 2024crwdnd2934271:0 jayeff crwdne2934271:0

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crwdns2934285:0crwdne2934285:0

Hi Jayeff, and thanks for your response.

I actually already have a dedicated LED tester. Photo amended to original post for your consideration.

The instructions that came with it explicitly said not to use it in the way you describe. (I think the wording was "Never test any LED strips while they are still connected", or something to that effect.)

For the record, it does work. I have used it successfully many times to identify faulty individual strips or LEDs for repair purposes. Just never when those strips were plugged into anything.

So is it that I can safely use it through the connector when the strip(s) is still plugged in? Or is that a function of some testers and not of others? It would be great to not have to fully disassemble a TV every time I want to test the strips and I wouldn't mind buying a different LED tester if that is a possibility only with another one.

Thank you for your time. — Justin Castle
@erelectronics

My understanding is that the LED strips (or rather the LED power supply cable at the power board) have to be disconnected from the power board, otherwise it would be trying to supply power both ways i.e. to the strips and back into the board.

You should be able to connect it between the LED+ lead and the return lead on the cable plug going to the LEDs for each strip (or feed if there's more than 1 strip per feed), so you should only have to remove the back cover to do this. — jayeff
@jayeff Okay. I have tried that and was able to power and get light from line LED1/VOut1 and tried the same but was unable to get any light from line LED2/VOut2.

I think this confirms the LEDs have gone out? At least, one or more of them on line 2?

Thank you for the advice. I genuinely didn't know I could use the tester in such a way. — Justin Castle
@erelectronics

The LEDs in a strip (and strips on the same feed) are in a series connection so it only takes one to fail open circuit and the whole strip doesn't light up.

You could try replacing just the individual faulty LED on the strip but getting one that has the same characteristics as the others may not be easy, so you may notice a brightness difference in that area of the screen, when it's working again. Also the others have aged so again might be problematic. Best to get a complete compatible strip or maybe replace all the strips given that one LED (or more) has failed. The probability is that the others may not be far behind anyway.

Looking at the parts link above for the repair kit, there are 12 LED strips in the TV (6 strips/power feed?) and the part number is LC470DUE-SFR1 LC470DUG-JFR1 (examples only to show cost of set of 12).

Usually the part number is printed on the strip itself, if you wish to confirm. — jayeff
Hi @erelectronics

Ran out of characters (1024) in my comment above but your LED tester supplies from 0-320V so it can be used to test individual LEDs on a strip, individual LED strips i.e. multiple LEDs in series on a strip, (both of the former are when access to the strips themselves has been achieved - screen assembly disassembled) and complete LED "feeds" i.e. multiple LED strips in series from the power board (TV back cover only removed) as usually individual LED power "feeds" e.g. in your case 2 feeds, will not exceed 320V DC anyway

Here's a video that shows how to replace the strips in the TV.

Apologies if you knew how to do this already. — jayeff

Vizio Television

Vizio E470i-A0, No power, suspect bad LEDs?

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