Vizio E28H-C1

[CapLeaker]

Re: Vizio E28H-C1

now you have a main board problem. No PSon and BLon.

[dick_barton]

Re: Vizio E28H-C1

Since you have changed the power supply, like CapLeaker I would be suspecting the main board since as he has stated you have no PS_ON or BL_ON

[Fisher77]

Re: Vizio E28H-C1

Do you get anything on pson when you push power button? Backlights? Check around mainboard input connector for fuses, voltages at regulators. Brown wire fluctuates when you push power button?

Voltage on the pson pin is .7V at all times, even when I push the button. Tried with the remote as well, no change.

Checked fuses around the main board input, all checked good.

Brown wire fluctuates with and without pushing the button.

I will check the voltages at the regulators.

[Fisher77]

Re: Vizio E28H-C1

Ok I checked the voltage regulators.

I think I may have found a problem with U703. It is a 903T63 low dropout regulator. Here is the datasheet for it:

https://www.digchip.com/datasheets/p.../G903T63UF.php

Ok the datasheet shows Pin1 as GND, Pin2 as Vout, and Pin3 as Vin.

When I checked the voltage on this regulator I found the following:
Of course 0V pin1.
Pin3 had 5V input
Pin 2 was fluctuating from .8V to 1.4V.
According to the datasheet that regulator should have 3.3V typical output.
Another thing I did was test the continuity. Of course pin 1 to ground buzzed, but pin2 to ground also buzzed. So then I checked continuity between pins 1, and 2 with a resulting buzz from the meter. Resistance between pins 1 and 2 was 1.6 ohms. From pin2 to ground was also 1.6 ohms.

Now I assume that this would indicate that the regulator is bad. But I wanted to run it by you all first, and ask Do I need to remove it from the board confirm that it is bad? Or does this indicate that it is deffinitely shot?

[dskall]

Re: Vizio E28H-C1

I would remove regulator then check board for short between pin 1and 2

[CapLeaker]

Re: Vizio E28H-C1

I would remove regulator then check board for short between pin 1and 2

x2

[Fisher77]

Re: Vizio E28H-C1

I would remove regulator then check board for short between pin 1and 2

x2

Yep, the board has a short between pin pads 1 and 2.

[dskall]

Re: Vizio E28H-C1

If you have external power supply you could put 3.3v with low current on pads 1 and 2. Freeze components around the regulator and see what thaws out first.

[Fisher77]

Re: Vizio E28H-C1

If you have external power supply you could put 3.3v with low current on pads 1 and 2. Freeze components around the regulator and see what thaws out first.

Will do. Thanks

[CapLeaker]

Re: Vizio E28H-C1

If you have external power supply you could put 3.3v with low current on pads 1 and 2. Freeze components around the regulator and see what thaws out first.

or use pure 99% alcohol.

[Fisher77]

Re: Vizio E28H-C1

Well I used the rest of the freeze spray I had, and did not find anything. I switched to 91% IPA that I had on hand. Put drops on just about everything, and still found nothing. I then removed the cover and heatsink from the eeprom after I noticed the cover felt a little warm. I put a couple of drops of IPA on the eeprom, hooked up the 3.3 volts and it almost instantly started evaporating the IPA. I stuck the board in the freezer for a bit to get it nice and chilly, put the IPA on the eeprom again, hooked the 3.3V to it, and again it almost instantly started evaporated the IPA.

The eeprom is the only thing I am seeing on the board that is evaporating the IPA that fast.

[CapLeaker]

Re: Vizio E28H-C1

Make a picture of the board first, then take that IC off and check if the short cleared. If it didn't, keep on going on anything that is on that voltage rail. It could also be a surface mount SMD cap shorted to GND.

[Fisher77]

Re: Vizio E28H-C1

Ok I finally got back to this TV. I removed the eeprom chip as suggested by CapLeaker. The short was gone after that, so it looks like the eeprom was the cause of the short. Ordered a new board and the TV fired right up.

Thanks for all the help with this.