Short Between Teensy 4.0 and Audio Shield -- Teensy Fails & Gets Hot!

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This took me a while to figure out... My Teensy 4.0 worked fine (with a connected LCD) but when I soldered an Audio Shield (Rev D, of course) under the Teensy, it stopped working and got quite warm. I triple-checked the orientation -- okay. I eventually figured out that one Teensy capacitor (C29) rests on the Audio Shield's SD (metal) card frame when the Shield is beneath the Teensy and the two are pressed together -- see the picture. I desoldered the Teensy, lifted it about .02", re-soldered and the problem cleared. A bit of Capton tape between the two is now called for in production. The picture has a cheesy piece of Scotch tape (too blurry to make out.) This is less likely to be a problem with the Teensy 4.1 because there are no big capacitors near the SD card cage. Teensy 4-0 and Audio Shield near-short.jpg
Those dupont male header strips are designed to be used with female dupont headers and that provides 1/2" clearance.
It seems you've just used the male headers as permanent board-to-board connector.
Can't really blame for that connection method when PJRC store itself shows similar examples on the product page :p (Though with better separation distances.)
To be clear: I am the idiot here. My application is very height-limited and I was so excited about getting to the audio portion of this project I wasn't thinking and just jammed the boards together despite years of cautious design! My only concern was whether I should solder the board in-place or run wires to it -- which would be ever so much easier to re-work. Anyway, it's great that (heat considerations notwithstanding) a little piece of Capton tape should allow 3 (populated) PCB layers to squeeze into 0.5" total height.
Some metal components are actually available with kapton tape pre-fitted - its the industry-standard way to fix this kind of issue ;)
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