Vizio XVT3D474SV: power but no video, suspected t-con failure

[unlimitedbacon]

Hi everyone,

I just picked up a broken Vizio VXT3D474SV from a friend. Reportedly, they had a technician come out and replace 1 or more of the circuit boards but the TV still did not work and it was declared dead. On bringing it home, I cleaned it up and powered it on. Amazingly, it worked absolutely fine for about 20 minutes. Then, as I was flipping through channels, the screen became garbled. I tried to reboot the TV but it does not want to power back on.

Symptoms:
* After plugging in power, TV goes through normal boot sequence (LED logo blinks amber/white for a few minutes), then settles into standby mode (amber LED)
* After turning on the TV with power button or remote, the LED turns white but nothing else happens. No sound, and no image (I checked using a flashlight). On rare occasions, the backlight will turn on, but usually it doesn't.
* After a few minutes, the TV reboots (flashing amber/white LED)

Diagnostics:
* All capacitors look undamaged.
* I have checked all the voltages coming out of the power supply and they are all good.
* I checked voltage drop and continuity across all the fuses (one large fuse on PSU and several ceramic fuses on other boards) and they are all good.
* I was only able to find one voltage regulator (a 7805 on the motherboard) and its output is nominal.

Here are a couple threads that describe the same issue:
https://www.badcaps.net/forum/showthread.php?t=38370
https://www.badcaps.net/forum/showthread.php?t=23735
https://www.badcaps.net/forum/showth...3D424SV&page=2
http://www.tv-forums.com/cgi-bin/gfo...9172837#154479
http://www.tv-forums.com/cgi-bin/gfo...9172837#152379

Pictures:
http://imgur.com/a/IrgLf

Based on all of this, I believe the problem is with the t-con board, but every place I have looked online is sold out of replacements (probably because this is a common issue with this TV). Thus, I would like to try and fix the board I have.

Since the TV did work momentarily, I think we can make some deductions. The faulty component must be one that became functional again after either sitting idle for a long time (weeks or months), or getting shaken during the car ride home. This component then failed after warming up (operating for about 20 minutes). Do you guys think this could be a capacitor issue? They all look fine but I know that doesn't necessarily mean they don't have problems.

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I was also thinking of trying to reflow the BGA chips, but I don't really want to do anything until I have a better idea of whats wrong with it. Does anyone have any advice? I have a crappy oscilloscope if that will help for anything.

[budm]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

We need to look at the common signals that the TV needs to operate, read my basic troubleshooting guide, your TV uses LED backlghts so it does not have inverter. We need to look at Standby voltage, PS_ON, Bl_on when the TV is off, when the TV is on, and when TV does not function.

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

Heres the signals you asked for and a few extra. There is nothing here labeled PS_ON but REMOTE ON/OFF seems to serve the same function. I'm not sure what LD ON/OFF does.

		Standby		On (not functional)
5V SB		5.10		5.07
REMOTE ON/OFF	0.00		3.29
LD ON/OFF	0.00		0.06
BL ON/OFF	0.00		0.01

12V		0.00		11.79
18V		0.00		18.73

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

Played with the TV a little more. On the rare occasions when the backlight comes on, audio also works.

[mmartell]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I say main board. Get out your hairdryer and warm it up.

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

The backlight seems to be working more consistently today. Not sure why. I tried hitting the motherboard with my heat gun, but it had no effect. Warming up the tcon also did nothing.

Heres an updated voltage chart with measurements from when the backlight turns on. Sometimes it flickers while it is running. Still no image under any circumstances.

		Standby		On (no backlight)	On (with backlight)
5V SB		5.10		5.07			5.09
REMOTE ON/OFF	0.00		3.29			3.29
LD ON/OFF	0.00		0.06			1.97
BL ON/OFF	0.00		0.01			3.28

12V		0.00		11.79			11.81
18V		0.00		18.73			18.63

[Boroth]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I am having a similiar issue with this same exact TV. I have the TCON board out and have reflowed all the chips that are covered with heatsinks. Afterwords I decided to go through and check out the caps on the board as several look to be slightly bulged. To my amazement it was two lesser caps that are producing some strange results.

Cap at CE28 is Labeled OE 470 EZD and when using the continuity feature of the meter (just a first test sort of way I like to check capacitors in circuit to test for blown out caps) this one is reading far far far lower then the other similarly mark caps on the board. The Buzzer is going off and it is reading 016 when all of the other fuses marked the same are reading in the 1380 range and no beep.

Cap next to it at CE8 is marked OP 220 CLA. Same thing....reading 014 and buzzer going off. Other caps marked the same on the board are all reading around 530.


Can you check what those are running for you if you still have access to this board please. May help me in the repair of this board!

[Boroth]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I should point out...my issue is different however. After the boot up flashing logo I can power the TV on and get the Vizio logo and then black screen. I can press the job button and see volumn control and channel selector and get into basic menu. However, this TV is not responding to ANY inputs. Will not respond to HDMI inputs...VGA(RGB) from PC or AV from DVD player. Do not have cable here so unable to check to see if that is working. Have checked every single fuse on all the boards and everything is good. The ONLY thing ive found are these couple caps showing weird numbers.

[budm]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

@unlimitedbacon, so it looks to me that, the BL_ON control signal from the main board is not present when the Backlights goes out.

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

@unlimitedbacon, so it looks to me that, the BL_ON control signal from the main board is not present when the Backlights goes out.

Yes. Normally this would indicate the motherboard but I am still leaning towards t-con for a couple reasons. First, I confirmed with my friend that the technician replaced the motherboard already. Second, even when the backlight comes on there is still no image. Finally, the threads I linked to in my original post describe identical symptoms and the solution was to replace the t-con.

Can you check what those are running for you if you still have access to this board please. May help me in the repair of this board!

I'm getting 6.6 ohms across both of those capacitors.

[budm]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I do not know but the BL_ON signal is separated signal, usually if they use an error signal from T-CON if the T-CON is bad, it will shut down the TV which means the PS_ON will be turned off. Your friend knows for sue that the used main board is good? You can try disconnecting the cable between the T-CON and the main board to see what you get, also check and see if you do have 12VDC at both ends of the SMD fuse on the T-CON board using chassis as the gnd ref.

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I've got 11.82 volts on both sides of the fuse. TV does the same thing with the LVDS cable disconnected. White LED comes on but no image or backlight.

[budm]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

Well, it still can mean that the main board is not sending the LVD SIGNALS to the T-CON board. You can take a chance changing the T-CON board, but I say it has bad main board but you will have to take chance on replacing the board, you will need the scope to find out if you do have LVD SIGNALS or not.

[Boroth]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

I have an update. So I reflowed the main board and the Tcon board today....all the big IC chips were all reflowed. Put everything together and the tv was working perfectly. Went through the whole setup process and after about 20 minutes the tv rebooted and then had a screen claiming it was automatically updating the Firmware and was updating it to the Aug 9th 2011 version mp-xp2.7.9_rc1 and to please wait while it the tv restarts. Well, it has been restarting over and over for the last 45 minutes. Goes through the flashing White and Amber phase.....V logo screen shows up...and then does it all over again. Over and over and over. Any ideas anyone?

[budm]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

How does it get the firmware from, USB?, and how did it do that by itself or you are trying to do the firmware updating? Sounds like the main board is still the problem.

[Boroth]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

it is a smart Tv and I had it connected to the internet. It autodownloaded it and started the update process.
Still has not come out of it

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

Boroth's TV would be getting firmware updates automatically over wifi.

I tried scoping the LVDS signals but its really hard because the pins are so tiny and I have a crappy scope. Some of the lines do change voltage when the TV turns on (looks like about 3V), but I havn't found anything that looks like a signal. Can you tell me a little more about what I'm looking for? What frequency and any pins in particular?

[budm]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

@unlimitedbacon, you will need to get the spec sheet of the LCD panel to get the pinout of the T-CON which it will show you all the signal pins, the signals can be in 100MHz range.

[unlimitedbacon]

Re: Vizio XVT3D474SV: power but no video, suspected t-con failure

So I tried baking the T-Con board to reflow the BGAs. Figured I had nothing to loose. It didn't fix it but it does something different now. The backlight comes on and it shows what looks like a test pattern. White screen with 3 vertical black bars dividing the screen into quarters.