Vizio E291-A1

[staze]

Hi All,

I have one of these TV's that just went dead on me. I don't have the PS values handy, but from what I recall, the PS-On and the DIM-On were both showing as 0V when the unit is on and off.

It does the typical power on, no backlight, sound, video, and won't turn off until you pull the power.

What's interesting is there's some definite "switching" voice coming from the main PCB. I'm not sure if that's due to the EEPROM being bad, and the CPU not firing up, or if something else is going on. That switching noise appears on both the "dead" PS-On and DIM-On lines measured with an oscilloscope.

I'm happy to buy a new EEPROM, but my big question is, what causes the corruption/failure? A batch of bad chips, crappy design of the display, failing regulators? I'm just worried that I'm going to have to keep replacing this IC every few years. =/

Attached is a picture of the main board. The EEPROM IC is a winbond chip. I thought I had a picture of just it, but I'm not able to make out the exact IC model. Also interesting is there's, what looks like, a silver sharpie mark on U408. Not sure if that's from someone confirming it worked, or what. If anyone has values for what various regulators should output, I can also check and confirm that. Seems like there are a lot of redundant VRs... several 3.3v regulators, several 5V regulators. Guess that's just cheaper than paying for an extra layer on the board. The build quality of these TVs is pretty darn crappy. =/

[dskall]

Re: Vizio E291-A1

Try freezing eeprom. May have bad capacitor if you have noise

[staze]

Re: Vizio E291-A1

swapped out the caps that seem likely, no change. swapped out VR, no change. Somewhere on that side of the board, there's a relatively low impedance path to ground (136R). So working on tracking that down. Guessing it's not the eeprom.

[staze]

Re: Vizio E291-A1

hmm... managed to get a replacement main board to test with, and shows the same symptoms.

So either it's the power supply (not sure how, unless one of the dim/on-off rails is shorted), or I have a blown LED backlight.

Any suggestions how to test?

[dskall]

Re: Vizio E291-A1

Need to post some voltages from power supply. Also unplug ir sensor and wifi if it has one. See if that changes anything

[staze]

Re: Vizio E291-A1

Okay, here we go:

Off, from the dim pin being pin 1.

0v
0v
0v
0v
0v
0v
0v
0v
0v
0v
5.2v
5.2v

On:

0v (50mv)
0v (80mv)
12.5v
12.5v
0v
0v
0v
25v
25v
4.5v
5v
5v

Disconnecting backlight makes no difference. Also tried pulling the pins for the dim and on/off and that made no diff. Have not yet tried to force them on with a 1k resistor between the 5v standby and the on and dim pins.

So either the new board I got is bad, or... it's not the main board.

[CapLeaker]

Re: Vizio E291-A1

The main board is returning PSon. That's good. However the main board is not turning the back lights on (On/Off). That is not so good. Bad main board.
SJ sells a main board repair kit that you could try, or get a new main board.

So if you disconnect the main board and jump STBY voltage to the PSon and the On/Off pins through a 1k resistor for each pin and plug the PSU in, the PSU should fire up and the back lights should be on.

[staze]

Re: Vizio E291-A1

So "new" board I got was also bad? Any chance it's something else? I'm happy to buy parts to replace, just want to make sure I'm not wasting more time. Also before I send note to ebay seller about replacement board.

Thanks!

[CapLeaker]

Re: Vizio E291-A1

PSon and BLon are generated on the main board. BLon isn't there, the main board is bad.

[staze]

Re: Vizio E291-A1

figured. thanks!

[staze]

Re: Vizio E291-A1

so, another question before the repair kit: what causes the failure? bad parts, bad power supply? some hardware design fault on Vizio's part?

[CapLeaker]

Re: Vizio E291-A1

could be low quality parts, some esd discarge etc... Vizio's are known for bad solders, bad voltage regulators, etc. However I don't think your PSU is bad.

The repair kit states that it "may" fix that problem. See what a replacement board vs the repair kit costs.

[staze]

Re: Vizio E291-A1

Got the repair kit from SJ, and it worked perfectly!

Thanks All!

[dick_barton]

Re: Vizio E291-A1

Can you say what components needing to be replaced were in the repair kit which could help others having the same problem.

[CapLeaker]

Re: Vizio E291-A1

glad to hear that your TV is up and running again.

[staze]

Re: Vizio E291-A1

So, hopefully SJ won't get mad at me, but the kit came with 4 ICs. The EEPROM (U409), and Buck converter (U704), and two mosfets (Q702 and Q706). Only thing I noticed was the thermal pad on the back of U704 wasn't soldered very well when I removed it. I made sure it soldered quite well when replacing it. Note, you'll probably want a heat gun/rework hot air station to remove that chip. You may be able to heat enough from the back of the PCB with an iron to remove it, but I've never had good luck with that.

Attached is the image of which ones get replaced.

[dick_barton]

Re: Vizio E291-A1

Thanks for the update. Will prove useful to anyone else who may have this problem.

[staze]

Re: Vizio E291-A1

=)

I'll note I bought the kit over ebay from SJ because it had free shipping. The amazon store from SJ was more, and directly from SJ had shipping. So, make sure to check. =)