Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

[alias_willsmith]

So upon opening this up, there was clear physical damage to EL408, so I replaced it. There was also damage to a few resistors and a capacitor directly connected to that transistor which were also replaced and which are on the opposite side of the board. However I still get no power at all when pushing the power on button, NOTHING. In the attached picture I have shown the voltage levels at each transistor leg. I have no idea what this part of the circuit was designed to do, so I'm clueless as to what reference levels should be at. I do know that AC is being delivered at least to that point on the board and that it's at least stable to that point. Initially whatever the original problem was also blew the mains fuse which I replaced as well. It has since not blown.

Hopefully, I've been clear in my description and someone can help me understand what the hell is going on with this one. How would I get a schematic for this to better understand things? It's been a while since my formal electronics engineering schooling and honestly, I'm way out of my element at this point. Thanks in advanced.

[budm]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

Please up load pictures of the whole back side of the TV so we can see how all the boards are connected together, then full board pictures of the top and bottom side of the power supply board.
There are more than one version of this model:
http://www.shopjimmy.com/catalogsear...=Vizio+E472VLE
This looks to be your power supply/inverter board? Vizio 0500-0405-1290
http://www.shopjimmy.com/vizio-0500-...t-inverter.htm
Are you sure you are not getting 5V standby Voltage feeding the main board?
Pictures provided by shopjimmy.

[alias_willsmith]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

See attached pics.

There is 5V on pins 1,2, and 3 of the connector that is circled in red. This connector connects to the other board which I assume is the control board. So yes, standby voltage is present, assuming the pins circled in red are the "standby"?

[alias_willsmith]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

Any takers?

[budm]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

See attached pics.

There is 5V on pins 1,2, and 3 of the connector that is circled in red. This connector connects to the other board which I assume is the control board. So yes, standby voltage is present, assuming the pins circled in red are the "standby"?

How about the DCV readings of rest of the PIN 8 through pin 14?

[alias_willsmith]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

pins 8 through 14 are all at 0v. What should these be at?

[budm]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

That means the main board is not sending the command signals to the power supply board.
You need to get that pin 11 P_ON/OFF of >2VDC first to turn on the rest of power supply, the rest of the pins are for the Backlights ON/OFF to turn on the Backlights Inverter circuit and Dimming control which you do not have either.

[alias_willsmith]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

So does that mean the likely cause is a bad main board?

When I connect the ribbon cable from the main board to the power supply board, the pins 1 through 3 start oscillating in voltage from under 1V to a bit over 3V. Is this normal? I can also hear a very very tiny "tick" coming from some component on the power supply board but only when the ribbon cable is attached.

Not sure how to proceed at this point. Any clues?

[budm]

Re: Vizio E472VLE, No power at all, blown transistor (replaced), still no power.

So does that mean the likely cause is a bad main board?

When I connect the ribbon cable from the main board to the power supply board, the pins 1 through 3 start oscillating in voltage from under 1V to a bit over 3V. Is this normal? I can also hear a very very tiny "tick" coming from some component on the power supply board but only when the ribbon cable is attached.

Not sure how to proceed at this point. Any clues?

Ah, that is the important information, so the readings of 0 on other pins were done without the cable between the power supply and the main board in place.
Fluctuating 5VSTBY with amin board connected can be due to bad STBY power supply or the main board is drawing too much current.
At his point I would inspect the main board really really well to see if it has any burnt, blown, or shorted out components.
BTW, what is the history of this TV? Was it hit by the surges or lighting near by?