Vizio VW37L HDTV20A Power supply No Standby Voltage

[Worminizer]

I have a Vizio VW37L HDTV20A with no power, no standby light, no response whatsoever. I pulled the cover, and tested all the rails on the power supply board, with no 0v on all rails. Even 5v standby voltage is missing. I have 67v ac at the big capacitor with reference to chassis ground. I have 67v ac at the hot side of the smaller transformer, but no dc or ac reading on the other side. There is no voltage anywhere on the cold side of the board. I am not experienced with transformers, so I'm not sure what could cause this. If I had the parts readily available, I would change the transformer. I have tested all the resistors and diodes that I could see.(though I could have easily missed one) No caps are bulging, and all but two have very low esr, the two with questionable esr are a 2.2uf 50v and a 1uf 50v. They are only at 1ohm. I have not changed them yet, because first, I wasn't sure if they would affect loss of standby, and second, I can't find a suitable low esr 1uf 50v cap on digikey. I have fixed other vizios with dc-dc voltage reg problems(u33 and the like) as well as some with bad caps on the board, and even one with a bad eeprom. This one is new to me, because tv repair is also new to me, I'm a fiber optic splicer for the giant corporation with initials. Any assistance would be awesome.

Thanks in advance,
Steve

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Also, here is a clear shot of the transformer I was referring to. I am probably way off base, but I am too dense to learn from anything but painful mistakes. They tend to stick.

[retiredcaps]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

1) We rarely ask anyone to do AC measurements. At the large filter capacitor, we are interested in DC V across the legs of the big cap.

It should be AC mains x 1.414 or roughly 165V DC if you live in the USA.

Do you get roughly 165V DC?

2) What is part number IC201 on the backside of the pcb?

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

yes, i have 169.21v dc

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

I will post pics of all the ic's that I took as soon as my phone stops acting up.

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Here they are.

[retiredcaps]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Refer to

http://pdf1.alldatasheet.com/datashe.../TEA1532T.html

for pinouts.

1) Measure the DC voltage of VCC with respect to GND.

2) Is the above stable or fluctuating?

3) One of the two electrolytic caps on the other side of IC201 is your startup cap. It is likely 47uF 50V. It's positive leg will have continuity to the VCC pin of IC201.

4) What is the DC voltage across the legs of the startup cap?

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

1-2) It seems to be fluctuating quickly between 55 and 56vdc.

3-4) The startup cap is fluctuating between 9 and 10vdc

[kevinm34232]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Worm are you using "hot" ground or chassis ground??

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

ok, I checked the rest of the pins, and they all seem to have similar voltages. Not all exactly the same, but here they are

1 51-52vdc fluctuating
2 59.3vdc stable
3 59.3vdc stable
4 59.3vdc stable
5 59.3vdc stable
6 58-59vdc fluctuating
7 59.3vdc stable
8 58-59vdc fluctuating

I couldn't find any indicator or circle that represents pin 1, so i started at bottom left if you are reading the writing upright. Most of the ic's that were marked with circles had them at the bottom left. If I am wrong, then just invert my readings.

[tom66]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

You need to use the metal frame of the TV (such as the LCD back plate) as your ground.

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

in order to get the readings on the bottom, I had to bench the board. I have the ground from the plug bolted to the corner hole, as it would be in the case, I don't know what else to do to get it close to how it reads in the set. Should I tie all four corners together to ground?

[tom66]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Can't you install the board in the TV and leave the connectors disconnected, then test that way?

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Sorry I'm a noob guys, ground is earth in my line of work, I'm not used to all these different potentials.

[tom66]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

Is this a singly or doubly insulated chassis? It is doubly insulated if it has no earth connection to your plug.

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

the connectors are not my hindrance, so much as i cant get to the ic he wants the readings from because its on the back of the board, against the lcd panel. The leads on the cap can't be reached even from the top, because the cap sits flush on the board.

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

The line from the ac plug has three leads, the pos and neg leads go directly to the board, and the ground bolts straight to the chassis. The four bolt holes on the board are grounded when it is installed, but out of the set, they have different potentials, and are not all common. Short of running a ground field around to all the holes on the board, and connecting that to the plug ground, I don't know what else to do to make it behave as it should out of the set to get the readings.

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

I can take a picture of the whole set fully assembled if you like.

[tom66]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

All those screws should be at the same potential as they're all bolted into the chassis. However, they might not all be connected on the PSU. You should use the chassis as your ground in this instance.

[Worminizer]

Re: Vizio VW37L HDTV20A Power supply No Standby Voltage

I created a quasi-chassis by tying all the points on the ps board that it touches the chassis together, as well as tying it to ground. If this doesn't work, the only thing else I can think of is getting some stand offs and bolting it in backwards.

Between the two leads of the startup cap, its fluctuating between 9-10vdc.

Here are my new voltages on the ic.

1 68-70vdc fluctuating
2 79-79.5vdc fluctuating
3 78-79vdc fluctuating
4 78-79vdc fluctuating
5 78-79vdc fluctuating
6 78-79vdc fluctuating
7 78-79vdc fluctuating
8 75-78vdc fluctuating