Vizio E371VL - Power Supply Problem

[pauldow]

Hello,

The current project is this Vizio unit. No picture, sound or logo light.
I found the 3.15A fuse was blown. It's the diagonal one at the upper left.
I replaced it, and it turned into a flashbulb when I plugged the set in.

The diodes at to the left of the capacitor seem OK, as does the bridge rectifier. The capacitor to the left of the fuse reads 92 uF while in circuit. It's labeled 68 uF.

I've got a question on the value of those two resistors left of the fuse near the heat sink. All the color band guides I see don't allow a black band to be at the end. It looks like the bands are red, black silver, gold, black. The middle band appears to be metallic, and not gray. Two metallic colors don't make sense either. My meter isn't extremely sensitive, so I show 0.4 Ohms on them. when I touch the probes together, I get 0.2 ohms. Does that sound right.

Does anyone have any hints on what to look at next?

Thanks,
Paul

[budm]

Re: Vizio E371VL - Power Supply Problem

That fuse is from the output of the PFC Voltage booster circuit, the shorts is more likely due to shorted SMD Power MOSFETs (4 of them on the bottom half of the board in the pictures) which drive the Inverter transformers. You need to find out if they are shorted out or not.
https://www.badcaps.net/forum/attach...4&d=1463429463

[pauldow]

Re: Vizio E371VL - Power Supply Problem

Hello Bud,

Thank you for the suggestion. I checked them, and don't get any short between any of the three leads. All four read pretty close to each other.

The part number on those is HF5N50

There's not a lot of circuitry to go wrong before the transformers.
The SMD diodes in that area seem to be good too.

I tried it again with all the connectors unplugged (except 110V in) and got the same blown fuse result.

[budm]

Re: Vizio E371VL - Power Supply Problem

Check the resistance between the negative leg of the main filter cap and the output side of the fuse to see what you get.
The shorts may be also in the standby power supply section, we can isolate that section once we see the resistance reading as requested above.

[pauldow]

Re: Vizio E371VL - Power Supply Problem

I've been working with the 'ol meter trying to trace where the low resistance is, but haven't pinned down the component yet.
I get 1.6 Ohms from the negative side of the filter capacitor to the output of the fuse.
I took out the capacitor, and it reads 151 uf, but it's a 68 uf 450V cap.
The resistance reading didn't change with it in or out though.
The semiconductor attached to the heat sink near the red top transformer is KF12M60. The M may be an H. The print is blurry. A search came back with nothing on either of those numbers though.
Measurements across those pins are 9 K Ohm minimum.

Thanks again for the help,
Paul

[budm]

Re: Vizio E371VL - Power Supply Problem

You can lift one end of the inductor (the one I marked in the picture) for feeding the Voltage from the fuse to the STANDBY power supply section to see if the shorts after the fuse will go away.

[pauldow]

Re: Vizio E371VL - Power Supply Problem

OK. It looks like that isolates the area where the problem is. With that inductor removed, I get 4.5 M Ohms from the end of that fuse to the negative side of the filter capacitor when I have the - lead on the fuse, and the + lead on the capacitor. It's an open circuit with the + on the fuse and - on the cap.

[OleICdude]

Re: Vizio E371VL - Power Supply Problem

Is the 68uf filter cap you took out leaky? Check with ohmmeter Rx1 forward and reverse.

[budm]

Re: Vizio E371VL - Power Supply Problem

That means the shorted circuit is in the standby power supply section.
So now we are going to isolate the SMPS IC150 (6-PIN TO-220 IC on the heatsink) by lifting one end of the GND return resistor R183 (0.39 Ohm), then check to see if the shorts after the inductor still exist, right now the shorts after the inductor should be there before lifting the resistor.
http://www.shopjimmy.com/vizio-0500-...-inverter.htm#

Pictures provided by shopjimmy.

[pauldow]

Re: Vizio E371VL - Power Supply Problem

Is the 68uf filter cap you took out leaky? Check with ohmmeter Rx1 forward and reverse.

I get over range with the leads touching in both directions.
When I change the range up to 100K, it starts increasing the resistance reading. I have a cheap capacitance meter, and it reads 63.8 Ohms.

So now we are going to isolate the SMPS IC150 (6-PIN TO-220 IC on the heatsink) by lifting one end of the GND return resistor R183 (0.39 Ohm), then check to see if the shorts after the inductor still exist, right now the shorts after the inductor should be there before lifting the resistor.

I put the inductor back in. Looking at the solder side of the board with the 110V connector at the bottom left, I get 1 ohm at the left side of that resistor, 1.4 Ohm on the right. With the resistor removed, I get 1 Ohm on the left side, and 100 Ohms on the right side of the resistor location.
All measurements are being done from the fuse.

I was poking around on the board to see if I could find anything, and the transformer seems to have a low resistance. That's the one with the yellow tape on it.
If I remove it, I got 3.9 M Ohms from the fuse to the negative side of the filter cap. I'm not sure how the transformer is wired since the numbers printed on it didn't appear when I did a search. On the hot side I get open circuit on the outer leads, and again on the inner leads. I get 0.8 Ohms on the two right pins (when looking from underneath) and 0.2 Ohms on the two left pins.
Could that be the evil part?

[budm]

Re: Vizio E371VL - Power Supply Problem

So, you are saying that when one leg of that resistor I asked you to lifti then you check the resistance between the inductor leg that you solder back in place, it still show <1 Ohms between the negative leg of the cap and the inductor? That is what we are trying to find out.
No it will not be the transformer, not even need to remove the transformer if you follow my instruction.
All the resistance reading right now is ref to the negative leg of the cap.
So the bottom line is what is the resistance you are getting between the negative leg of the filter cap and the the inductor (resistor back in place) when that ground return resistor R813 has one leg lifted off the board?

[pauldow]

Re: Vizio E371VL - Power Supply Problem

So the bottom line is what is the resistance you are getting between the negative leg of the filter cap and the the inductor (resistor back in place) when that ground return resistor R813 has one leg lifted off the board?

Sorry about that. It's a fine line between me trying to not to be too much of a pest to you, and well, being a pest.

I get 100 Ohms from the inductor to the - side of the filter capacitor when R813 is out of the circuit.

[budm]

Re: Vizio E371VL - Power Supply Problem

You need to remove that IC next.
BTW, can you read the P/N of that IC?

[budm]

Re: Vizio E371VL - Power Supply Problem

Sorry about that. It's a fine line between me trying to not to be too much of a pest to you, and well, being a pest.

I get 100 Ohms from the inductor to the - side of the filter capacitor when R813 is out of the circuit.

You put the transformer back in place?
You need to remove that IC next.
BTW, can you read the P/N of that IC?

[pauldow]

Re: Vizio E371VL - Power Supply Problem

Yes, the transformer was back in for that last measurement.
The part number of that device is STR W6053N
The last line on that part says 1D141, but I figure that's some manufacturer number.

[dano69]

Re: Vizio E371VL - Power Supply Problem

You can lift one end of the inductor (the one I marked in the picture) for feeding the Voltage from the fuse to the STANDBY power supply section to see if the shorts after the fuse will go away.

What is the number for that inductor