42" Vizio GV42L Speaker Static Noise Overlay Problem

[tieny]

Just got a Vizio GV42L that has a bad sound problem. When I plug in hdmi, all I hear from the speakers is loud static and noise. I can barely hear the sound coming from a movie because its covered with static.

Opened up the TV and checked the connection to the speakers. Near it was some capacitors but they checked out with low esr and within specs. I tried connecting my own speakers that I salvaged from another TV but I get the same static noise coming from it, so the connections and speakers can be ruled out.

So what else can cause this bad static sound from the speaker?

[tieny]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

Photo of where the speaker connection is on the main board.

[999999999]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

In the pic, up and to the left on the heatsink, appears to be a chipamp chip. Get the markings off of it to find the datasheet, the pinout, and begin probing with a multimeter to determine if the positive power rail (and negative if/since it appears to be a split rail design, due to it looking like the speaker output doesn't pass through output coupling capacitor(s)) is within the expected range.

Also probe for audio signal (AC) voltage fluctuations on the L & R audio inputs, as well whether there is any significant (beyond a few mV) DC voltage present, which there shouldn't be. Keep tracing back the circuit until you find a reading that looks wrong, when you come to the next IC, repeat the above pulling the datasheet and taking readings. If the circuit is difficult to follow, look around as one or more of the SMD SOIC8 chips pictured may be opamp(s) handling the audio signal.

[tieny]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

Well Ugh, I just made matters worst... I was probing around the power supply while I placed it upside down, and there was a spark and a little burn mark on the heatsink. And now the TV won't turn on... I checked the main fuse which was open and just replaced it but still no luck.. =( won't turn on.

Measuring across the biggest cap I'm getting about 170V. I'm getting standby voltage 5.12V. So what just happened?

[tieny]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

Actually, think I found the problem. Found an open fuse on the main board also.

[tieny]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

Just replaced the main board fuse (thank god for salvaged parts :]) and everything is back to normal. Whew.... Now I can get back to my initial problem.


Are you talking about the component on the heatsink?

The label on it is: TDA8946AJ

[rmoody]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

I have a box full of boards for this tv that came from a broken screen. If you need anything lmk and I'll cross reference my numbers with yours.

[tieny]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

I found the data sheet for that component on the heatsink, (TDA8946AJ)

I'm measuring 5.96V on the output of the main board where the speakers are plugged in.

The only thing I see on the datasheet is Vcc has a range: 4.5V - 18V
So then what are the specs of all the other pins? I have no idea how to read this datasheet..

I'll probably just take a guess and replace TDA8946AJ. Does anyone know where I can get this part? Theres one on ebay but I rather not wait one month for shipping from china... =/

[drpj23]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

See if anyone on ebay is selling that main (or any other Vizio main) as is or broken. Just make sure that it has that chip but that could be an alternative.

[999999999]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

If your measurement of 5.96V is DC, that would explain the blown fuse. There should be under 1V DC, preferably only a few mV (approaching 0mV). Is it 5.96VDC on both the left channel to ground, AND on the right channel to ground?

Whichever channel it is, you'll want to measure the signal input on that channel, it'll be either pin 6 (IN1+) or pin 12 (IN2+), might as well measure both. Neither should have more than a few mV of DC voltage. IF either has more than a few mV, then the problem is happening before that power amp chip and it is only amplifying the problem.

If neither has more than a few (dozen) mV, suspect the amp chip but measure the power rail voltage at pins 3 (Vcc1) and 16 (Vcc2) as it should be within the spec sheet range of 4.5V to 18VDC, probably this product is set up to use 12VDC or more.

I'm not sure what chipamp ICs have a close pinout to the TDA8946, but besides the locations of the pins (the problem/issue), otherwise there should be some equivalent functionality 2 channel / 15W into 8 ohms chips that you could substitute but you'd need to air wire from the chip leads to the PCB, and it would probably be a good ideal to put a 0.1uF capacitor between the Vcc pins and Gnd at the chip. Given the choice I'd rather wait for a month to get the right chip from China, hopefully it's genuine instead of fake.

[budm]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

The IC uses bridge direct couple output setup, 2 amp per channel, so the output pin 1 & 4, 14 & 17 will be sitting at 1/2 VCC. If you measure at the both pins of the each speaker connector, it should be 0V, but each output pin and ground should be 1/2 VCC.
Do you get bad sound on ALL input, not just the HDMI?
How about the audio line out at the RCA jack, do they sound OK there?

[tieny]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

I'm getting bad sound on all input. I tried to even hook on the DVI to my laptop and test the aux input but every time it reads the DVI signal the TV actually just shuts of...

[tom66]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

This is one application where tracing with an oscilloscope is almost essential, but you may be able to make do by setting the output volume low and tracing the signal through with an audio jack and computer speakers.

One question, is noise level dependent on the volume?

[budm]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

But do also you get bad sound at the RCA AUDIO line out? if you also get bad sound at the Audio line out, that will eliminate the TDA IC problem. We need to find out if it is the pre-amp sound processor problem or the audio output problem.

[ecking767]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

I have a GV42LHDTV main board that have a problem with the digital turner. The tuner wouldn't scan for digital channels. So I replaced the main board and sold the TV. The audio was working with no problem.

If replacing the audio chip doesn't fix your problem. You can use this board for components values and parts replacement

You are more then welcome to have the board just pay the cost of shipping

[Dgtech]

Re: 42" Vizio GV42L Speaker Static Noise Overlay Problem

I have this same type TV in my basement right now from a co-worker. I am currently working on a monitor and waiting for parts. Once I get that done this week, I will start on this Vizio GV42L with a similar problem. What he complained of was a buzzing sound. I'll keep checking back and let you know what I find out if it is the same.

Vizio simply sucks.