Vizio E500i-A0 backlight goes out intermittently

[llabourdeth]

My TV started dying a while back. It turns on and always has sound, but after a while (a few minutes in the beginning, now often only a few seconds) the screen goes dark. Using a flashlight, I determined that the backlight turning off, so that's where I started troubleshooting.

I'm confused by my troubleshooting test results. See photo attachments courtesy of ShopJimmy for reference. Power board is 0500-0605-0280. With the TV on, the connector to main board measured:
1: 5v
2: 5v
3-5: 0v
6: 12v
7: 12v
8: 3v
9: 3v
10: 3v
11: 3v
On the LED connector:
LED1-: 3v
LED1+: 68v
LED2-: 3v
LED2+: 68v

At one point during testing, the part of the backlight came on and I measured 113v on LED1+ which slowly came back to 68v when the light went out. All this made me think I had bad LED strips, but that's where it got interesting.

With the LED connector unplugged, I applied the leads of the led backlight tester to the connector and was able to get both LED1 and LED2 to illuminate.
I haven't removed the panel to check that each individual LED lights up, as I don't want to remove it unless I have to.

Does anybody have any thoughts? Do I need to replace the LEDs? or is there something else that I'm missing?

[budm]

Re: Vizio E500i-A0 backlight goes out intermittently

68V is the input Voltage feeding the LED boost converter circuit which boosts the voltage to over 100V. So you have to monitor both LED + pins to see what you have when it is working and when it is not, you have two LED driver for two set of LED strings.

[dskall]

Re: Vizio E500i-A0 backlight goes out intermittently

Vizio drives there leds over 400ma. Your tester drives them around 300ma. If you leave tester on for awhile the strip may fail as they get hot. Since yours are intermittent they will need to get hot to show failure.

[budm]

Re: Vizio E500i-A0 backlight goes out intermittently

I believe those LED tester only putting out <20 mA.

[dskall]

Re: Vizio E500i-A0 backlight goes out intermittently

Sorry retested about 30ma

[llabourdeth]

Re: Vizio E500i-A0 backlight goes out intermittently

...you have to monitor both LED + pins to see what you have when it is working and when it is not.

I forgot to mention that. While the tv was somewhat working, I think only string 1 was on by the time I thought to investigate: the display looked blotchy. LED1+ was at the aforementioned 113v and LED2+ was still 68v.

Vizio drives there leds over 400ma. Your tester drives them around 300ma. If you leave tester on for awhile the strip may fail as they get hot. Since yours are intermittent they will need to get hot to show failure.

So I'll need to replace some LEDs. The strips are out of stock and have been for a while, so I need to do some soldering. Is it plausible to pinpoint which ones need replacing by driving the string with the tester and applying heat to each led with a heat gun? Or should I just plan on replacing each and every one?

[dskall]

Re: Vizio E500i-A0 backlight goes out intermittently

You should be able to find the bad ones with tester. Also make sure connections between strips are good

[dkeener]

Re: Vizio E500i-A0 backlight goes out intermittently

Hi Folks. Also Working on a Vizio e500i-a0 which has a similar issue to the one in this thread but not quite as severe. Display has a dim horizontal band which is about one third of the screen height. The proper stuff is in the band... its just dim. The rest of the screen is fine and nice and bright. I checked LED1 and LED2 pins on the power supply board and found LED1 at 67v and LED2 and 113v. I removed the cable and tested LED1 and 2 open circuit and got 67v. What i found searching indicated that this pointed to LED problems. I bought a new set of LED's and replaced them but still have exactly the same problem.

Any thoughts?? Thanks.

[dkeener]

Re: Vizio E500i-A0 backlight goes out intermittently

68V is the input Voltage feeding the LED boost converter circuit which boosts the voltage to over 100V. So you have to monitor both LED + pins to see what you have when it is working and when it is not, you have two LED driver for two set of LED strings.

Where is the LED boost converter located?

[budm]

Re: Vizio E500i-A0 backlight goes out intermittently

https://www.badcaps.net/forum/attach...5&d=1497448943

Top right section where the two yellow inductors are.

[dkeener]

Re: Vizio E500i-A0 backlight goes out intermittently

https://www.badcaps.net/forum/attach...5&d=1497448943

Top right section where the two yellow inductors are.

Ahh... Ok, thanks. So if I am holding at 67v on LED1+ and I have already changed LED's, does that imply that my issue is really on the power supply board? What triggers the boost converter to increase drive above the open circuit 67v?

Thanks!

[budm]

Re: Vizio E500i-A0 backlight goes out intermittently

Since LED2 has the boosted Voltage then the BL-ON signal is fine.
There are two LED driver ICs (IC390/490 16-pin SMD): on the top left side.
https://www.badcaps.net/forum/attach...6&d=1497448943

So look up the spec sheet of the IC and then you can also do the Voltage comparison test. Check the MOSFET (Q302/402)/DIODES (D301/401), solder joints, etc. in the booster section.

[dkeener]

Re: Vizio E500i-A0 backlight goes out intermittently

Since LED2 has the boosted Voltage then the BL-ON signal is fine.
There are two LED driver ICs (IC390/490 16-pin SMD): on the top left side.
https://www.badcaps.net/forum/attach...6&d=1497448943

So look up the spec sheet of the IC and then you can also do the Voltage comparison test. Check the MOSFET (Q302/402)/DIODES (D301/401), solder joints, etc. in the booster section.

Replaced the power supply board (eBay $42) and all works fine now.

Thanks!!!!

[budm]

Re: Vizio E500i-A0 backlight goes out intermittently

Thanks for follow-up.