Prop Shield Blown amplifier??

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Waterme11on

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Hey guys,
I'm making a Sound project with the teensy 3.2 and prop shield, currently I've stripped my teensy of all components except the speaker coming out of the prop shield + and - pins, and the unit is powered by usb.

My problem is that at any volume above extremely quiet, any sound that comes out of the prop shield is super distorted and clipping. When played at full volume the sound doesn't even come out just a popping/distorted sound.
This happens on any type of waveform, and also on many different sketches. The prop shield was working fine for a few days and I think I bumped it too hard and it suddenly went like this.

I know its not a code issue since I have 2 identical teensy+prop shields running the same code and the other one works fine.
I have tried replacing the speaker and even the cords running into the speaker, makes no difference.
There doesn't seem to be any shorts or external damage.

The only thing I can think of is that the Amp has broken, however I don't see how this could happen given that i'm not pushing any extreme volumes/clipping, and my other teensy is still running the code just fine. Also the bump it received was minor, like I didn't throw it against the wall...

Questions:
Is there any way for me to test if the problem is due to the teensy or due to the prop shield?
Is there any way to reset the amplifier or something to fix it?
Is it possible that I broke the amplifier by bumping it?
Has anyone else experienced something like this?
Am I going to have to buy a new prop shield/Teensy?

Thanks.
 
Is there any way for me to test if the problem is due to the teensy or due to the prop shield?

Differential diagnose: Plug prop shield A to Teensy B and vice versa. Then EE diagnose: Check input and output signals of the amp and compare with the working system.
Is there any way to reset the amplifier or something to fix it?

Depends on what is broken. When you are really sure that only the amp is
broken, the LM48310 is $1.xx at mouser. Soldering skills required.
Is it possible that I broke the amplifier by bumping it?

Yes. Maybe just one or more SMD solders on the prop shield are broken. Reworking the prop shield could be a solution if you have the equipment.
Has anyone else experienced something like this?

At least not documented in these forums.
Am I going to have to buy a new prop shield/Teensy?

Depends on the differential Diagnose. See above. It's highly improbable that both are broken. Identify which of both is the culprit. Whatever it is, one is less that $20. Waisting a working hour for an unsuccessful try to fix it might be more expensive.
 
I've only seen one other report of PROP AMP issues - it was mine July 2016: PROP_LC-Hot-Amp-Chip

I have a Prop shield where the AMP goes HOT to touch within seconds of it being enabled - everything else works. Is this heat showing up on yours?

Thanks Thierry - I see it at digikey.com … LM48310SD - but no fun to hand solder?

I figured it would be easier abort the AMP and maybe swap the 8MB flash for 16 MB version and repurpose it.
 
Hey thanks for the reply Theremingenieur,
Both of my teensys are hard soldered onto the prop shields and i'm not taking the working one apart to test the broken one.
Might snip the broken unit off and if I can't see any visible, fixable damage i'll just get a new one.. :\
I don't have a heat gun or any experience in soldering those tiny chips so looks like buying new will be the faster/cheaper way, plus I can keep this one intact for any led-only projects that I might have in future.

Is there a way i can hook up a speaker or line out jack directly to the teensy and see if the audio is distorting there?
 
Is there a way i can hook up a speaker or line out jack directly to the teensy and see if the audio is distorting there?

It will be hard if the T3.2 DAC pin (A14) is soldered to shield AudioIn. If you can isolate the DAC pin, you could look at it with a scope or attach it to a breakout amp+speaker (e.g. https://www.sparkfun.com/products/11044). Or set the DAC to various values and use a volt meter to confirm. Another simple test is to jumper DAC to an ADC pin and check values with a sketch like
https://github.com/manitou48/teensy3/blob/master/dacadc.ino

The DAC pin can only source about 1 ma so don't hook it directly to a speaker/headphone/earbuds.
 
Sorry for the weird phrasing in this post, was going to make a new thread but I realized it would be better to continue here. Sorry for repeating some info.

I now have two prop shields with broken amplifiers, both from receiving an impact akin to being dropped from shoulder height. More specifically, Inside a custom poi that I dropped whilst spinning.

The teensy/prop shield was inside a 3d printed case made from Durable resin, a shock proof material. The cases are solid but flex on impact. The actual teensy units are screwed into a piece of laser cut PETG, which is suspended in between both halves of the cylindrical case.
Basically they were rigidly mounted, and not able to bounce around in the case, or touch any side of the case.

After being dropped the most recent amplifier stopped making sound, and instead now emits a buzzing distorted noise that doesn't resemble the original sounds being played.
The first time this happened the amplifier would put out the original sound but heavily distorted and buzzing, however this one received a smaller impact.
I've taken a look at the prop shield and there's no external damage to the traces, or any of the components and their connections.

Do audio amplifiers have some sort of weakness to vibration and impact?


I have two poi with the exact same system inside and the other one is fine and has withstood multiple drops, and even has a crack on the case but still works.
I also have some earlier prototypes that are made from the same material, and one has even been thrown at a brick wall with force and is still working.

Maybe i've just been unlucky with two faulty units but I don't want to just keep buying new prop shields every time they break. I need to know if there's a way I can combat this type of malfunction.
 
Just stop throwing everything around - it's not made for that. ;)

No, seriously : Circuit boards with soldered SMD components are definitively not shock proof. The PCB material is flexible which can cause the copper traces to crack and the tiny solder points (sometimes not visible because below the ICs) tend to break. Thus, although the components might be still fine for themselves, the connections between them might be broken. Did you ever think of mounting your stuff with small rubber shock absorbers in the housing?
 
I won't stop until I can smash it against the ground and still get sound coming out :p

I think you're right, I need to modify my design to have the teensy mounted on a shock absorbing system.
I realized that having everything rigid is actually worse since the shock is 100% transferred through to the electronics.

I also remembered that the model I had thrown against the wall had the teensy held in hot glue, and was also more isolated from the exterior case, so that would have dampened the shock way more.

Thanks for the advice, i'll update how I go.
Eventually i'll get to the stage where I can purposefully abuse them without worry... Annoying and expensive to test though :\
 
Wow I think i figured out why only the amps inside the unit with the bluetooth unit broke.
The teensy is kinda near the edge of the case, and with the bluetooth unit, pins 0-2 have wires on them with shrink wrap. These wires are touching the edge of the case, and the pins line up with the audio amplifier on the prop shield.
When the case was dropped, the force was being translated from the case through to the pins and causing a bend directly at where the amplifier, sits, which probably caused the invisible damage, broken traces etc.

I'm still going to shock proof the design for maximum security, move the teensy away from the edge, and add rubber spacers under the teensy.
 
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