Teensy 4.1 bricked card reader after touching the pins

[fdr]

I have two identical Teensy 4.1 boards and one of them stopped recognizing the SD card (probably after touching these pins on the back). The second board still works fine with the same card and the same sketch (CardInfo.ino). Is this a hardware failure? Is it possible to fry the board by touching +5V and the place under the card slot with your hand? What can I measure to test this?


I performed a hardware reset by holding PROGRAM for 12 seconds but the card is still not recognized - "Initialization failed" or SD_CARD_ERROR_DMA 0x25
each time I use

chipSelect = BUILTIN_SDCARD

which works fine on the second board

 

[MarkT]

Any CMOS chip can be fried by touching, as they are static sensitive and anti-static precautions should be followed when handling them. The first steps to this are banishing nylon carpets and nylon/synthetic clothing, using a conductive workbench (even wood) and anti-static wrist-band. Low humidity in the air exacerbates the problem.

Accidentally shorting 5V to any of the T4.x pins can fry the chip immediately, its absolutely not 5V tolerant - but this would require something more conductive than skin to do.

 

[fdr]

Thanks for the reply. I touched it only by hand by holding in both hands, not by the wire connected to 5V pin. So it may be a static electrocity because I don't have a wrist band.

But I wonder why all other pins are still working as well as all sketches, I just cannot using the card. The 3.3V pins are also working and everything is compiling without problems.

 

[PaulStoffregen]

I have no way to know what really went wrong.

But regarding the question on the bottom side pins, I can say none of those pins are shared with the SD socket. Here's the relevant part of the schematic.



Electro-static discharge is always theoretically a possible explanation, but pretty unlikely in this case. The 6 signals and 2 power lines for the SD card are routed on internal PCB layers, and the SD socket is a grounded metal shell (mostly) surrounding the signals.

For a completely blind guess, mechanical stress or damage on the SD socket would be a much more likely explanation.

 

[fdr]

Thanks Paul, I'll examine the socket with a macro lens. Should there be any voltage on the DAT, CMD, CLK pins on an empty socket?

 

[PaulStoffregen]

Should there be any voltage on the DAT, CMD, CLK pins on an empty socket?

Those pins have digital pin numbers assigned.



The best way to test involves loading the LED blink example with the pin number edited so you put a known signal on a specific pin.