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Old 10-05-2020, 12:30 PM   #1
Computer_Eng
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Default Vizio Soundbar VSB200B Overheating

I have a Vizio soundbar Model VSB200B which is overheating. This is evidently a common problem. The symptom is, during normal operation, the sound cuts out and its leds flash an error which indicate the soundbar has detected an overheat condition. After a short while, the unit goes back to normal operation, but having the audio cut in and out makes it unusable. I tried adding a fan to one of the ventilation slots which helped for a while, but now the problem has returned.

I opened the unit up and couldn't see any obvious area on the control board which might be the source of the overheat condition. The significant IC on the board seems to be an Avnera AV8112A, but I can't locate a datasheet for this component. Avnera was acquired by Skyworks in 2018.

My assumption is that one of the chips has an on chip thermal detection circuit and my next try is to glue some heatsinks on a few of the candidate chips.

Does anyone have a fix for this problem or experience in repairing this soundbar?
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Old 10-11-2020, 10:03 PM   #2
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Default Re: Vizio Soundbar VSB200B Overheating

Generally, finding a schematic or service manual for "newer" electronics like this is a little harder. So if you have any pictures of the internals of the sound bar, it may be helpful to post them here (please attach to the forums using built-in feature rather than external hosts, as those can be hit-or-miss with loading images for everyone.)

My guess (almost willing to put a $100 on it ) is that there is at least one class-D amp somewhere... and perhaps this may be the culprit that's overheating. If it was the "main IC", I suspect the whole soundbar would power-cycle instead of just the sound output. But who knows.

And of course, the cutting in-and-out could also be a bad solder joint somewhere or a voltage regulator?

Is it a wireless soundbar, by the way? (Well, I guess I can check that from the model number, but would be good to confirm and also ask if you're using a wireless device for sound output or wired.)
*EDIT*
Yeah, nevermind that last comment. I see that this soundbar doesn't have any wireless/blutooth garbage.

Last edited by momaka; 10-11-2020 at 10:12 PM..
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Old 10-14-2020, 10:07 PM   #3
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Default Re: Vizio Soundbar VSB200B Overheating

Here are photos of the top and bottom of the main board.

You are correct, there is no bluetooth capability.

The power output seems to be from dual FDD8424 Dual N & P Channel MOSFETs on the back side of the board. No external heat sinks, so likely a Class D as you speculated.
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Old 10-16-2020, 09:18 PM   #4
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Default Re: Vizio Soundbar VSB200B Overheating

Hmmm...
I'm a bit split where to start on this one. Indeed nothing looks obviously bad or overheated.

Since the unit seems to be consistently indicating over-temperature, perhaps you can check if any of the ICs or MOSFETs are getting extremely hot during operation (i.e. run the unit without covers and check temperature by hand or perhaps with something more fancy, if you have any such tools.) I see the input power supply on this unit is listed as only being 24V DC, so that should make it pretty safe to probe/touch inside the device. See which parts (if any) get so hot that they feel like they are burning and note them down.

The right side of the board where MOSFETs Q1 and Q4 are seems ever so slightly darker, perhaps indicating one of these is running hot (Q4 in particular.) But that could also be the lightning of the picture, of course.

In any case, if you do have a multimeter, you can check these MOSFETs with the power off (and PSU disconnected) for any potential short-circuit or low-resistance readings between Gate, Drain, and Source for the MOSFETs in each package - i.e. measure resistance on the lowest scale on your multimeter between the following and post what results you get:
MOSFET XX
Resistance between G1 and D1
Resistance between D1 and S1
Resistance between G1 and S1
Resistance between G2 and D2
Resistance between D2 and S2
Resistance between G2 and S2

Then repeat that for the other MOSFETs. Perhaps we can get a few quantitative readings that way to help us see which readings may be normal and which may be "outliers".

Another thing I can't help but notice is the cheap electrolytic cap brands used in this unit. I don't expect them to be the issue here, but with cheap cap brands it's never certain. If any of these are letting through too much noise from one of the voltage regulators on the board, that too could be causing the IC to malfunction/glitch or not communicate with other components properly, thus triggering the issues we see. So replacing the caps (with good quality Japanese low-ESR/impedance ones) is another option to consider while troubleshooting this.

I also can't seem to find a datasheet that exactly matches the package for IC10 and IC11, but most datasheets suggest these are LE15AB voltage regulators (for 1.5V output.) With power plugged in, check what voltage you are getting on each of the pins (relative to ground) on these two ICs. Try both while the soundbar is Off/standby and when turned On.

I suppose that would be all for now. Let's see what results/info you come out with, and maybe we can use that to guide us further.

Last edited by momaka; 10-16-2020 at 09:23 PM..
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Old 10-25-2020, 03:06 PM   #5
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Default Re: Vizio Soundbar VSB200B Overheating

Here is an update of the VIZIO soundbar. The error I'm getting now is an "over-current error" (different error than the original "overheating condition") The manual says "Over-current detection is indicated, reduce the volume setting of the Sound Bar and Subwoofer temporarily, and turn the unit off for a short period and back on to reset the circuitry. If this indication continues to occur, then reduce the volume level for the particular source content being played."

I removed all source inputs, disconnected the speakers and turned down the volume and still get an over-current error.

I used an IR thermometer and the only warm sections of the board are near U1 and IC14 (~ 100F). U1 is a Cirrus Logic CS48520CQZ which is an audio processing DSP, so the temp seems reasonable. IC14 is marked C5K (or maybe LC5K) and I can't find any information on this part.

I measured all 24 Drain/Gate/Source permutations on the output MOSFETs and there were no shorts. The MOSFETS are only slightly above room temp when powered.

The input supply appears steady at 24VDC. The test points labeled 1.8V and 3.3V are in range.

The output of IC10 (the 15AB low drop regulator) was 5V and IC11 (a 16AB) was 1.8V. I had to guess on the outputs as the data sheet I located was for an S0 8 pin package and not the SOT 5 pin on the board.

I may attempt to determine how the board is measuring the overcurrent condition as a next step.
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Old 10-26-2020, 08:53 PM   #6
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Default Re: Vizio Soundbar VSB200B Overheating

Quote:
Originally Posted by Computer_Eng View Post
Here is an update of the VIZIO soundbar. The error I'm getting now is an "over-current error" (different error than the original "overheating condition") The manual says "Over-current detection is indicated, reduce the volume setting of the Sound Bar and Subwoofer temporarily, and turn the unit off for a short period and back on to reset the circuitry. If this indication continues to occur, then reduce the volume level for the particular source content being played."
So what (if anything) brought this change in behavior? Did you test the soundbar differently? If there is a change in the error/problem without you doing anything different, that should be noted as a possible clue for later on.

Quote:
Originally Posted by Computer_Eng View Post
I removed all source inputs, disconnected the speakers and turned down the volume and still get an over-current error.
Right.
Given that when you had the over-temperature protection kicking in without anything playing from the soundbar, clearly this is not related to playing audio too loudly.

Also, I'm surprised the manual would include such a comment to suggest that if the volume of the input device is too high, it could cause an over-current condition. Any properly designed audio device / amplifier (at least anything that isn't cheap crap) should have a limiter / clip detector circuit and automatically limit or cut the audio input if it's too loud. Given how much electronics and "smart" circuitry these new gadgets pack nowadays, it would be ridiculous to think there is no such feature here. But I digress with that...

Quote:
Originally Posted by Computer_Eng View Post
I measured all 24 Drain/Gate/Source permutations on the output MOSFETs and there were no shorts. The MOSFETS are only slightly above room temp when powered.
OK, no shorts.
But what about the measurements? Did you at least see a pattern in the readings between the two output channels?

Quote:
Originally Posted by Computer_Eng View Post
I may attempt to determine how the board is measuring the overcurrent condition as a next step.
Sounds like a plant to me.

Keep in mind also that the over-current and over-temperature problems that the soundbar is detecting may or may not actually exist on the board. It could be that whatever monitoring circuitry is responsible for these protections has a malfunctioning component. Or worse, it could also be a firmware bug and/or error.

Since there isn't a schematic for this thing, I'd suggest to perform a basic check on all SMD passive devices on the board (i.e. look for shorted/low-resistance ceramic caps, open resistors, and etc.) After that, also check all transistor and diode discrete devices too, if possible. You very likely won't be able to get a proper reading for everything while still installed on the PCB, but at least it may give you a clue if something is quite off (like for example, a ceramic cap measuring less than 30 Ohms regardless of multimeter probe orientation - I'd call that one suspicious for sure.)
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Old 10-30-2020, 02:47 PM   #7
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Default Re: Vizio Soundbar VSB200B Overheating

The trajectory of the failure mode has been as follows. Initially, the unit would occasionally flash an error code and while the error code was flashing, the audio was disabled. After a short time, the error indication would reset on its own and the audio would come back on. I believe the original error code was for an overheat condition, but itís possible it was an overcurrent condition (which could have happened if I miscounted the error LEDs and got off by one as the two error LEDs are adjacent.) I installed a cooling fan on the enclosure and that helped for a while, but then the error returned and would cycle on/off to the point the unit was unlistenable. Now the error code is definitely the overcurrent condition and it is more or less continuous, even with no input and the output speakers disconnected.

I examined the main board closely and the output circuit seems to be a full-bridge Class D amplifier. The left and right channels are identical and each channel has two dual FDD8424H MOSFETs as the primary power switching components. The dual MOSFETs are connected to ground and +24VDC and drive the speakers in an ďHĒ or bridge configuration. One MOSFET pair is Q1/Q4 and the other is Q2/Q3.

I looked to see if there were any components that might detect overtemp or overcurrent conditions. One possibility is a thermistor which could measure temperature near the MOSFETs. There is a thermistor as part of each channelís circuitry (RT1 & RT2) and is physically near the MOSFETs. The thermistor does not have a part number. There are also low value resistors (R17, R18, R166 and R167) in the driver circuits and based on their value could be used to measure current. They are marked R100 and in circuit they measure zero (I'm guessing they are .1 ohm).

I probed the board with power on and noticed that one channel has a steady 3 VDC on its speaker output (unloaded). I looked at the MOSFET gate voltages and the MOSFETs should off. I think Iíll try swapping in a couple of new MOSFETs and see if that makes a difference. If that doesnít work, Iíll probably wave the white flag on this repair.
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Old 10-30-2020, 07:25 PM   #8
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Default Re: Vizio Soundbar VSB200B Overheating

Quote:
Originally Posted by Computer_Eng View Post
The trajectory of the failure mode has been as follows. Initially, the unit would occasionally flash an error code and while the error code was flashing, the audio was disabled. After a short time, the error indication would reset on its own and the audio would come back on.
Interesting.
Intermittent problems like that are usually more indicative of a bad solder joint or component getting out of spec.

Quote:
Originally Posted by Computer_Eng View Post
I looked to see if there were any components that might detect overtemp or overcurrent conditions. One possibility is a thermistor which could measure temperature near the MOSFETs. There is a thermistor as part of each channel’s circuitry (RT1 & RT2) and is physically near the MOSFETs. The thermistor does not have a part number. There are also low value resistors (R17, R18, R166 and R167) in the driver circuits and based on their value could be used to measure current. They are marked R100 and in circuit they measure zero (I'm guessing they are .1 ohm).
Good to know.
Even if one of the output MOSFETs does turn out to be bad, we still shouldn't discard the possibility of one these thermistors being out of spec and throwing up the over-temp error... or whatever circuit is responsible for reading them to not work quite right maybe.

Quote:
Originally Posted by Computer_Eng View Post
I probed the board with power on and noticed that one channel has a steady 3 VDC on its speaker output (unloaded). I looked at the MOSFET gate voltages and the MOSFETs should off. I think I’ll try swapping in a couple of new MOSFETs and see if that makes a difference.
Sounds like a plan.
Before you do that, though, you can also try just removing the MOSFETs on that channel (or even both channels) and then try to turn On the soundbar (and try with and without the speakers connected) to see if it throws an over-current error again.

Quote:
Originally Posted by Computer_Eng View Post
If that doesn’t work, I’ll probably wave the white flag on this repair.
Well, I just noticed your location in your profile, so feel free to PM me if you want a 2nd pair of eyes looked into it. I don't think I'm that far away from you.
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Old 10-30-2020, 07:32 PM   #9
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Default Re: Vizio Soundbar VSB200B Overheating

if you can work out what reports the overheating fault you can then work out if its working as intended then figure out why its happening . i know easier said than done but its a plan .
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Old 11-02-2020, 05:37 PM   #10
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Default Re: Vizio Soundbar VSB200B Overheating

Quote:
Intermittent problems like that are usually more indicative of a bad solder joint or component getting out of spec.
I agree. It does seem like the failure is consistent with a component gradual drifting out of spec.

I removed the two dual MOSFETs from one of the channels and it eliminated my flashing error code. Now the unit does not give me any errors, which is an improvement. However, the channel I left intact is not working (no audio output, even with an input signal.) This is not what I would have expected unless there's a problem with the remaining MOSFETs.

For now, my plan is to put a couple of new MOSFETs in and see if I at least get one channel back.
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Old 11-03-2020, 09:11 PM   #11
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Default Re: Vizio Soundbar VSB200B Overheating

Quote:
Originally Posted by Computer_Eng View Post
I removed the two dual MOSFETs from one of the channels and it eliminated my flashing error code. Now the unit does not give me any errors, which is an improvement. However, the channel I left intact is not working (no audio output, even with an input signal.) This is not what I would have expected unless there's a problem with the remaining MOSFETs.
That makes me wonder if the class D driver IC(s) for the MOSFETs is working correctly. And on that note, I'm trying to figure out which of the ICs is the class D driver. The Cirrus Logic cs48520cqz appears to be the DSP... so I don't think that's it. Then there's the HC4066, which appears to be a quad analog switch (i.e. probably used for switching between analog inputs 1 and 2.) So that seems to leave only the large AV8112A chip, which I can't seem to find a datasheet for.

On a different note... when you did the above test with the removed MOSFETs, did you try sending signal through all three inputs (i.e. the two analog RCA ones as well as optical S/PDIF)? I'm just also wondering if somehow the DPS is sending bad signal to the class D driver IC (whatever that may be) and this causing the voltage offset you saw on one of the channels. Perhaps food for though for later on.

Quote:
Originally Posted by Computer_Eng View Post
For now, my plan is to put a couple of new MOSFETs in and see if I at least get one channel back.
Sounds good. Keep us posted.
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Old 11-07-2020, 10:44 AM   #12
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Default Re: Vizio Soundbar VSB200B Overheating

Still waiting for the MOSFETs to show up. They're overdue, but at least they're in transit now. I ordered them from a supplier in NY which was the only ebay vendor shipping from inside the U.S. The choice was getting them quickly or cheaply (i.e., mailed from China). Could have ordered from Mouser or Digikey, but wanted to save on shipping.

Quote:
That makes me wonder if the class D driver IC(s) for the MOSFETs is working correctly. And on that note, I'm trying to figure out which of the ICs is the class D driver. The Cirrus Logic cs48520cqz appears to be the DSP... so I don't think that's it.
The gate drive circuits for the MOSFETs seem to be from the large Avnera AV8112A chip. If you look below the AV8112A there are four groups of discrete components near C10, C11, C23 and C24. The gates of the MOSFETs connect to either those capacitors or directly to the AV8112A. If they go to the caps, then the other side of the cap goes to the AV8112A.

Quote:
Then there's the HC4066, which appears to be a quad analog switch (i.e. probably used for switching between analog inputs 1 and 2.) So that seems to leave only the large AV8112A chip, which I can't seem to find a datasheet for.
I took a look at the control signals on the HC4066 analog/digital switch and rotating among the inputs to the soundbar appear to cause different members of the quad switch to be enabled, so I believe your theory is correct.

Quote:
On a different note... when you did the above test with the removed MOSFETs, did you try sending signal through all three inputs (i.e. the two analog RCA ones as well as optical S/PDIF)?
I've tried both of the analog RCA inputs with no difference. Haven't tried the optical yet.

For what it's worth, the circuit board appears to have come from AURA Sound. They have a web presence, but their web pages are in chinese. Interestingly, they claim the company originated in the U.S.
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Old 11-12-2020, 01:49 PM   #13
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Default Re: Vizio Soundbar VSB200B Overheating

I swapped in a new pair of MOSFETs on one channel, but no joy. When I turned the soundbar on, one set of speakers put out a brief burst of static, followed by silence and then the unit returned to the over-current error code.

I think this is the end of my attempts to revive the soundbar. Thanks to momaka and petehall347 for your suggestions along the way.
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Old 11-15-2020, 09:11 PM   #14
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Default Re: Vizio Soundbar VSB200B Overheating

You're welcome and sorry to hear this didn't work out.

I was going to suggest to throw a few more tricks at it (freeze spray, remove thermal sensors, and etc.), but I suppose that is a moot point now.

I guess now you have a subwoofer and soundbar that don't have anything to drive them. Maybe something for a future project, if you're into that stuff?
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