With nothing on the GPIO pins (including no fan shim) the I2C works normal. sudo i2cdetect -y 1 completes all addresses near instantly. Mount the Fan Shim, mechanical only - no software: I2C fails. sudo i2cdetect -y 1 takes over a second per address How to prevent the Fan Shim from interfering…

Fan Shim blocks I2C

PiTinker November 10, 2019, 6:44pm 2

I considered making a dumb shim, but pins 3 & 5 are not so easily circumvented

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