Vizio E701i-A3 backlight only and now no backlight

[Awsmessymail]

Hello all,
I’ve tried to repair TVs in the past with some luck. Toms repair manuals got taken down and now thats a bit harder.
I picked this TV up hoping for a quick fix. When the TV would power on, only the backlights would come on. The owner told me they heard loud screeching before it shut off. This alone makes me want to think the main board has an issue.
As I researched, I found the TCON/driver boards were an issue on this unit. I went in troubleshooting the TCON but found good voltages on the TCON. I followed shop jimmys guide to test the transistors and they seem okay. I also went through freaks first few pages of troubleshooting and no changes (I think this is correct since shop jimmys tutorial had me check common failure points of the TCON.)

freaks post:
https://www.badcaps.net/forum/troubl...but-backlights

shopjimmy checks:
https://youtu.be/yTnkOfwBGGE?si=lmBwShQZkWVISjcm

I then found the repair manual and tried to come back another day to see if I could make sense of it. I propped the tv up on the wall to try and make sense of voltage readings on the main board, etc. when I went to power on and make a post here, the backlights didnt come on. Nothing came on.

I started checking CN201 connector voltages and saw there was approx 2.1 volts on BL ERR pin. There was missing voltage on tcon on and 12v tcon.

i jumped pin 1 to pin 11 (LED ON) with a 100 ohm resistor and the backlights came on. BL ERR was now approximately 0. I went ahead and jumped pin 1 to 15 (tcon on) and saw that pin 14 went to 12 volts (12 v tcon).

I dont think I shorted anything out or did anything between troubleshooting sessions to cause this. I am assuming the main board is bad, but I would like to find out how to troubleshoot this further to fix why the unit only had backlights previously. I would prefer to not buy a full main board since the TV is pretty old at this point and not worth dumping 100-150$ into.

Any advice on where to go from here? Id really like to start understanding this stuff a bit more and how boards/voltages work together.

please let me known if you can supply some troubleshooting guidance to check the main board and also to check what component failed on the main board. What derives the BL Err voltage?

thank you in advance!

[nomoresonys]

When you did the jumper did you have about 12 volts on each side of the tcon fuse?

[Awsmessymail]

Where is this tcon fuse?

I did notice that when its jumpered I no longer have voltage across the silver roung cap (on the right side of the Tcon photo). I had voltage there when I did have backlights.

[nomoresonys]

Probably F101

[Awsmessymail]

Sorry it took so long to reply.

yes f101 has voltage on both sides of the fuse, indicating that its good (when jumpered on power supply board as mentioned previously).

any other ideas?

[Awsmessymail]

All, bumping this post.

hoping to get some help here so I can start learning/get this TV going.

[Awsmessymail]

Bump, still needing some help please!

have a good weekend!

[nomoresonys]

Try a simple test, check the vdc of that connector with your bl-error, check all 15 pins, report voltages here, give good description, so we don't have to keep going back to the picture, check with tv plugged in but off/standby, make note, now leave probe where it is and turn tv on, make note, so it will be like PS-on, standby xxx voltage, tv on xxx voltage.

[Awsmessymail]

Hello,
Sorry for taking so long to reply. This project took the backseat as we had our first kiddo this year. My wife is now wanting the repair room thrown in the trash so I'm trying to get everything fixed up and learn again. When plugging the TV in, it seems like the backlight now is working great but still no picture. I must of been a dummy and just hit the power button lol.

I assume standby is just plugging it in (backlights still come on) and that turned on is when you hit the power button (Backlights shut off).

At the PS connector that goes to the main board using a fluke 87V:
T CON_ON: STANDBY: APPROX 1.75V TURNED ON: 0v
12V T CON: STANDBY: 12.41V TURNED ON: started at 2.1v and appeared that it would bleed down to 0v. took meter off around 1.2. assume this is from a cap.
NC: NO WIRE/CONDUCTOR
LED-BR: STANDBY: APPROX 1.117V TURNED ON: APPROX 1.89 THEN WENT TO 0V
LED-ON: STANDBY: APPROX 1.8V TURNED ON: 0V
BL-ERR: STANDBY: 0.031V TURNED ON: 0V
12V REG: STANDBY:12.39V TURNED ON: 0.65, APPEARS TO BE BLEEDING DOWN TO 0. ASSUME THIS IS A CAP
12V REG: STANDBY: 12.39V TURNED ON: 0.65, APPEARS TO BE BLEEDING DOWN TO 0. ASSUME THIS IS A CAP
GND: STANDBY: 0V TURNED ON: 0V
GND: STANDBY: 0V TURNED ON: 0V
GND: STANDBY: 0V TURNED ON: 0V
12V AUDIO: STANDBY: 12.39V TURNED ON: 0.45V, APPEARS TO BE BLEEDING DOWN TO 0V.
PS-ON: STANDBY: 3.33V TURNED ON: 0.09V
AC-DET: STANDBY: 3.454V TURNED ON: 3.456V
3.3V: STANDBY: 3.368V TURNED ON: 3.369

After taking these measurements I can only assume that the when plugging in, the TV goes into on mode and when I hit the power button I assume its going into standby.

Do all these voltages look normal? Can you confirm or shed any light on what you are looking for here? I understand most of then but some I don't. I.e. LED-BR and LED-ON.

[nomoresonys]

Seems to be a mainboard issue, mainboards are a tough animal to troubleshoot, haven't had much success fixing them myself.