I am wondering if this board, which I recently purchased, was DOA.
I just connected it up and it appears not to be working correctly. I have it hooked up to a 3.3 V motherboard with an SH connector on it, attached with a Qwiic jumper cable. GND, 3.3 V, SDA and SCL are connected to the SH connector. I have checked several times that all pin-outs and connections are correct.
The motherboard uses a pyboard as the controller so I am using micropython to access the combo board. The motherboard works fine to access I2C devices on the motherboard. I disabled the I2C pull-ups on the combo board since the motherboard has pull-ups. The I2C addresses already in use on the motherboard are (in decimal, before left-shifting): 64,68,69,65,72,80-83 and 84-87. There should not be any conflicts with the combo board I2C addresses, which I left at the default settings: 0x5B and 0x77. You don’t spec if those are before or after left-shifting the address but either way there is no conflict: 0x5B would be (in my “units”) 91 if not yet left-shifted or 45 if already left-shifted, and 0x77 would be, respectively, 119 or 59.
However, when I attach the combo board (connecting the pyboard I2C bus to it and supplying GND and 3.3 V), the supply voltage drops to 1.7 V (!) and micropython cannot find any I2C devices on the motherboard or the combo board, or finds totally bogus ones, or I get an micropython IO device error. Exactly which of these happens apparently depends on the height of the moon or something.
The disturbing thing is the huge supply voltage drop, from 3.3 V down to 1.7. The regulator on the motherboard can easily handle the 13 mA of combo board load. That load does more than double the existing motherboard load but the regulator (an NCV4274) has enough heat-sinking on it to supply 200-250 mA or more. It’s pretty obvious why no I2C devices on the motherboard cannot be found when their supply voltage is only 1.7 V.
This all makes me think the board was DOA.
