Fried Audioboard

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Beervangeer

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Hi there,

I am using a audioboard with teensy 3.6 for a while.
Today suddenly the audioboard started to smoke.
The chip in the middle got burned.

When i put the usb in the teensy.
The center part of the audioboard starts to heat up.

I removed all the other cables from the teensy and still heating up a lot.

Anyone a idea what can cause this?
I guess the audiboard is done right?
 
Would be helpful to know if any other pins were used - or parts connected, and perhaps some photos showing how it was attached. Connections to audio out jack, or other in/out signal pads on Audio board? Any use of any of the GND pins on that board?
 
I quickly detached everything out of panic, so dont have picture now.

The following was connected:

RFM unit using:
* SPI2 pins
* Ground and 3.3v on teensy

A tft touch screen.
* SPI1 pins (alternative because of audioboard)
* ground on teensy
* 3.3v for reset screen on teensy
* vin on teensy to power screen

A led disk
* running on its own power source
* a ground connected to the board, otherwise when teensy is attached to pc i get disturbences
* two digital pins for clock and led controll

A minijack is going to external speakers also externally powered.

After removing everything, the audioboard still heats up.
 
Others can confirm - but reading: https://www.pjrc.com/store/teensy3_audio.html

It notes that: "It supports stereo headphone and stereo line-level output" and "output high quality audio to the headphones or line out pins. "

... Using powered speakers from the installed "headphone" jack may have been the issue. There may be definitive notes from PJRC in other threads
 
Using powered speakers on the headphone jack instead of the line out pins may short the VGND to GND, causing exactly the symptoms as described above.

A quick look onto the audio board schematic shows that the HP output is capacitorless which leads to the logical conclusion that the HPVGND of the SGTL5000 has a DC offset of VCC/2 which is a common practice nowadays for many headphone ICs to save PCB space and production cost. This DC offset is generated and buffered inside the chip, shorting it to GND kills everything.
 
Hard to imagine what would cause the SGTL5000 chip to actually burn up. Photos of how everything was connected would be needed to have any hope of figuring this out...

Quite a lot of power is needed to do this, more than can usually come from the USB because of the 500 mA PTC fuse. Maybe stuff with external power was somehow connected?
 
Ye to bad i disconnected the wiring, so i cant make a picture.

Like thermingeineur said, maybe it is the amplified speakers.
I did change to some other speakers with different amplifier.
I connect the minijack to this board: https://www.adafruit.com/product/1752.
This audio amplifier board was connected to a 5v adapter.

Before i used the minijack also with amplified speakers that have less power.
So i didnt realise that this could be a problem, because it worked for months with the other smaller amplified speakers.

I bought a new audioboard and will use the line out this time. Thanks theremin for the tip, hope i dont burn it again.
 
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