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CoffeeCoffeeCoffee
Joined: 23 Sep 2009
Posts: 11
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 Posted: Wed Sep 23, 2009 5:40 am Post subject: Vizio VW42L HDTV10A No Picture or Sound |
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TV Info:
Vizio VW42L HDTV10A
Part #10235020022
Serial #LSPALBH4238741
Manufacturing Date: October 2007
42" 1366x720p
Problem:
I was watching TV with my son a couple of days ago when I noticed some slight picture distortion (almost like interference) near the top of the picture for ~5-10 seconds. It was a couple of inches down from the top of the unit - the movie we were watching had the letterbox bars on the top and bottom of the screen.
Right after that the video on the TV went out.
At the same time the video went out the speakers started buzzing (it was a somewhat high-pitched buzzing).
The white "on" light stayed on on the front of the TV.
The remote and controls on the TV were unresponsive to turning the TV off.
I had to unplug the TV to shut it off.
After plugging the TV back in the orange standby light would came on.
Pressing the power button both on the remote and on the unit itself after plugging it back in would cause the orange standby light to turn white (on), but I don't get any video or sound. Also the backlight turns on, as I can see it illuminated in the bottom corner of the screen and the whole screen slightly illuminates as well.
So far I have taken the rear cover off of the TV and visually inspected the power supply board and the main board for any signs of damage, and I've checked for bulging caps. I didn't find anything out of the ordinary.
I was only able to find 1 fuse so far, located on the power supply board, and it tested good.
So now I'm hoping that someone might be able to help me figure out what the problem is, because my electrical skills are basically limited to automotive electrical circuits. I also really don't want to have to buy a new TV right now.
Thanks,
Dan |
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Justmanuals
Joined: 21 Aug 2004
Posts: 1948
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CoffeeCoffeeCoffee
Joined: 23 Sep 2009
Posts: 11
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| Posted: Fri Sep 25, 2009 4:12 am Post subject: More Info |
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I checked some voltages coming off of the power supply board.
At the fuze I couldn't get a constant reading - it kept jumping around all over the place between 180 and 255 volts. I used the chassis as earth ground for this check.
On the big capacitor (the only one) from earth ground to each of the two legs I got 347 and 56 volts. Measuring across both legs I got 400 volts.
Shortly after powering the TV on (maybe like 2 seconds after I hit the on button) there's a blue LED on the master inverter board that comes on for 2 seconds. For the first second it stays on solid, then for the second second it fades out to off.
On the master inverter board the input voltages were as follows (tested on earth ground):
23.3 (Ground wire on connector)
23.3
23.3
23.3
0
0
0
0
0
4.11 (this wire and the next one are not on the slave inverter board)
3.068
From ground wire on the connector to each of the other wires:
0
0
0
23.3
23.3
23.3
23.3
23.3
19.19 (this wire and the next one are not on the slave inverter board)
20.19
Readings from the 2 capacitors on the master inverter board (to earth ground) were 0 on the negative terminal and 23.3 volts on the positive terminal.
The slave inverter board had the same readings as the master, except for that the slave doesn't have the extra 2 wires furthest away from the ground wire.
The wires on the connector going into the main board from the power supply tested as follows (reading taken from all wires to earth ground):
3.15 (ground wire)
12.3
12.3
12.3
0
0
0
5.13
5.13
5.13
3.067
4.10
From ground wire on connector:
9.14
9.14
9.14
-3.14
-3.14
-3.14
1.988
1.988
1.988
-81.9mV
.959 V
Coming off of the main board I measured the speaker wires also (going to earth ground) and got:
Wires going to the left speaker:
6.07
6.11
Wires going to the right speaker:
6.05
6.07
I measure almost 0 V between the two wires for each speaker (should be kind of given anyway with the readings from above...).
Don't know if this will help or not, but at least there's some extra info  |
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minnie
Joined: 18 Aug 2005
Posts: 2880
Location: Hell
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| Posted: Sun Sep 27, 2009 2:01 am Post subject: |
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| Caps block dc and pass ac if you read dc across the cap it's shorted... Any caps bulged in the power supply? |
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CoffeeCoffeeCoffee
Joined: 23 Sep 2009
Posts: 11
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| Posted: Sun Sep 27, 2009 2:24 am Post subject: |
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There's no bulging caps that I can see on any of the boards, including the power supply.
So, I shouldn't be measuring a voltage drop across the terminals of the big cap then?
I just checked the resistance of the cap with the cap drained. It started up around the 20 Meg-ohm range and slowly dropped. I only held the meter on until it dropped to around 12 meg-ohms. After that I got a small voltage reading that started around 270mv and steadily and slowly dropped as I held the meter on it.
Maybe I'm thinking about caps wrong, but I thought that they acted somewhat like a fast-acting battery, or as a power conditioner to smooth out voltage spikes and dips...
In any event, thanks for the reply. |
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CoffeeCoffeeCoffee
Joined: 23 Sep 2009
Posts: 11
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| Posted: Thu Oct 08, 2009 5:45 am Post subject: |
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| Would anyone happen to know if parts from another VW42L HDTV10A with Serial # LSPBLBH would be interchangeable with mine (Serial # LSPALBH)? |
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krytron
Joined: 05 Sep 2009
Posts: 28
Location: Europe
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| Posted: Thu Oct 08, 2009 3:50 pm Post subject: |
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| minnie wrote: | | Caps block dc and pass ac if you read dc across the cap it's shorted... Any caps bulged in the power supply? |
This is incorrect. Caps block DC current, meaning there should be a DC voltage drop across a capacitor - an open circuit is the best DC blocker, and there would normally be a DC voltage drop over open circuit.
Actually, your statement is contradictory: if the cap is shorted, the DC voltage on it would be (near) zero, not some sane, "readable" value.
Quite the opposite for the coil - it passes DC (practically shot circuit for DC current), but for AC current it offers inductive resistance, i.e. one can measure AC voltage on the coil.
At least they told me so, but maybe they were lying to me. |
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Royalman
Joined: 28 Oct 2009
Posts: 6
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| Posted: Fri Oct 30, 2009 2:14 am Post subject: Coffee |
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| Just wondering if you have had any sucess with your project? |
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OldIBMer
Joined: 21 Aug 2009
Posts: 27
Location: USA
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| Posted: Sat Oct 31, 2009 4:16 am Post subject: |
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Given the OP's voltage readings, does it appear the inverter is being prevented from firing the backlight?
Is there something he can do to attempt to fire it?
And isn't it unlikely that the inverter is bad since the audio is out and that would imply two separate problems?
Gerald |
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CoffeeCoffeeCoffee
Joined: 23 Sep 2009
Posts: 11
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| Posted: Tue Nov 03, 2009 3:03 pm Post subject: |
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| Royalman wrote: | | Just wondering if you have had any sucess with your project? |
Not yet, I've been busy getting things ready for winter.
| OldIBMer wrote: | Given the OP's voltage readings, does it appear the inverter is being prevented from firing the backlight?
Is there something he can do to attempt to fire it?
And isn't it unlikely that the inverter is bad since the audio is out and that would imply two separate problems?
Gerald |
I think that the inverters are good - the backlight comes on when I power on the TV.
Because of that, and with the voltage reading from the power supply I don't think that the power supply is the problem either. Since I don't have any sound I don't think it's the LCD controller.
So that leaves the main board as being the best probable cause of the problem.
I just ordered a main board last night for $105. I should get it within 5 days, so we'll see how it works out... |
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