Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

[DXseekerMO]

I bought this Vizio E55-C2 yesterday with the complaint of completely dead, will not power on, no initial power light that trails off when plugged in. The complaint is confirmed.

The 120V protection fuse is good. The first thing I checked was main cap voltage, always at 385V. Other voltages found on the power board look like the TV is trying to tell me it's partially on? Here they are:

Main cap…….385v stable

1: 5VSB……….5.05v stable
2: 5VSB……….5.05v stable
3: ACD…………3.3v stable
4: PS_ON…….3.3v stable
5: GND………..18 ohms according to my meter
6: GND………..16 ohms according to my meter
7: 12V………….12.11v stable
8: 12V………….12.11v stable
9: GND……….. .018ohms
10: GND……… .013ohms
11: 12V………..12.11v stable
12: 12V………..12.11v stable
13-15: nc

The 20V rail is dead on all pins, plugged in to the main board or not. The grounds are good. The power board has an output rating for 20V printed on it so it must come from the power board?

I accidentally plugged the 20v connector back in while the unit was plugged up to the wall. I got an arc flash on one of the ground pins when I plugged it in, a pretty good one too. See the black spot on pin 8 and the connector body?

Also, I checked for PS_ON voltage change at the main board connector for the power button. Voltage drops from 3.3v to 0v when the button is pressed. I also checked for remote response by testing for voltage at the IR sensor board test points. The voltage does drop to different levels depending on what button is pressed on the remote. There is no voltage change at the power board when the power or on buttons are pressed on the TV or remote.

I pulled the power board, tested components in the 20V circuit and I see oddball readings, like diode test readings of .170. I saw readings like this on my LG 60PB6650 Y-sustain and found shorted MOSFETS.

The processor on the main board is warm to the touch when plugged in.

I see some things here that tell me both the main and power boards have problems. I was wondering if anyone can confirm this or maybe point me in a diagnostic direction from here?

Thanks everyone!

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

If you are getting 12 volts, you should be getting the 20 volts also as its from the same transformer.
If the PS_on line is changing I would expect the microprocessor is working, It could be that you don't have any backlights.
It seems the backlight power supply is part of the main board.

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

Thanks for the reply. The backlights are hooked up to the main board. I did re-confirm 20v is absent. That makes me wonder if something from the transformer to the 20v pins are open, or maybe the main board is sensing something amiss in the backlights and turning the 20v off?

If it weren't for the missing 20v I'd probably be diagnosing this as a bad main board.

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

I'm sorry, I must issue a correction here. The 20v rail is making 20.4 volts, or just enough to make my meter go OL in the 20v position

The 20v is present, main board hooked up or not.

Super glad you said that R_J, that made me go re-check to see what I missed!

Looks like its time to pop the main board and break off some high quality pictures.

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

Main board pix

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

Start by checking the F3 fuse, lower left corner in picture #2 It is a small smd fuse about 1/2 inch from the corner of the board

[DXseekerMO]

AAAAAAAAAAAAAAnd we have a winner!

Have a look at what I found. Looks like a shorted cap to me.....and it appears to have blown that whole area to smithereens! LOTS of damage!

R_J, Fuse F3 is good

[DXseekerMO]

Good fortune continues....

I just bought a NEW main board off ebay from a supplier close by for $21.00

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

It does'nt look that bad, clean it up, it might just be a shorted chip cap. here is a shopjimmy photo.

[budm]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

It does'nt look that bad, clean it up, it might just be a shorted chip cap. here is a shopjimmy photo.

It does look like just the C33 (MLCC) just shorted out which is the typical failure mode for the MLCC.

[DXseekerMO]

After clean-up of failed cap.....

R_J, I went ahead and cleaned it up. It's cooked real good! It looks like when the cap blew, it blew the trace back over on itself off the board, folded completely flat! It also looks like the trace is gone from under the cooked side.

Look carefully, the edge of the trace is pointing right at the camera after I folded it back a bit.

I guess I like them well-done!

Hey budm, hows it going?

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

I've repair board that were a lot worse than that. remove the blown cap, repair the trace with a small piece of wire, replace the cap, and it might be fine?

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

Challenge accepted!

Any idea how I'm going to get the spec from the blown cap?

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

What is the number on U2? check its datasheet
or if you have a capacitor checker? check the value of C52 off the same pin of U4, they look about the same. Or just try a 10 uf/50 volt elec. in its place

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

So the datasheet for U2 must call for a specific value cap off that leg? I don't have a cap checker but if projects like this keep coming in I'll probably get one. The one on my Harbor Freight-O-Meter is only so helpful, very basic multimeter with slotted terminals and few test modes.

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

So whats the number on U2? It is a ldo regulator ic I doubt the value is critical

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

The number is 54227, apparently the part number is TPS54227. Here's the datasheet link:

https://www.alldatasheet.com/datashe.../TPS54227.html

The callout is 4.5V to 18V Input, 2-A SYNCHRONOUS STEP DOWN (SWIFTTM) converter.

It looks like pin 6 is in circuit with the blown cap. It's callout is: Supply input for the high-side FET gate drive circuit. Connect 0.1 uF capacitor between VBST and SW VBST 7 pins. An internal diode is connected between VREG5 and VBST.

There appears to be a mix-up on the datasheet, seems as if they have pins 6 and 7 swapped around in the picture and description below it.

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

I'm having a hard time seeing the board, it is pin 8 its in circuit with. Its callout is VIN, input voltage supply pin.

If I'm reading the diagram correctly the input bypass capacitor is the one that is blown?

If it is, it looks like its calling for a 10uF cap?

Picture courtesy of ShopJimmy

[R_J]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

Check the resistance between pin 8 and 6 and then pin 6 and ground to make sure the ic's input is'nt shorted, then repair the trace (or install a 1Ω resistor or 1amp fuse to connect the trace) and try the board, you may not even need that cap just to try the board. or just put a radial 10uf/50v cap

[DXseekerMO]

Re: Vizio E55-C2, appears dead, no 20V, main cap always 385V, no PSon

The reading between pin 6 and 8 is OL

The reading between pin 6 and 5 is 370ohms.