Thanks. Herewith a report of my progress, or lack thereof. 1. I was using a Nano clone, a servo controller clone, and a power supply for each. Controller power is just for the servos, it gets chip power from the Arduino. I'm using the standard Adafruit test software. And I've used the controller clone before with success, so I don't think there's a design flaw there. 2. I've replaced each hardware piece with another, one at a time. No joy. I've tried SDA/SCL on the analog pins and on the digital pins. No joy. I've run the I2C scanner on both pin sets and found nothing. I've checked all the wiring for continuity and even looked for bad solder joints. Nothing. 3. I did find that the servo power supplies I tried tested at 5.9v and 6.2v at the connector plug. Once I plugged them in they both dropped to something under a volt. On both servo controllers. Probably normal, since I've seen it on multiple boards. 4. Finally, I replaced the nano with a uno. Still get no movement out of the servos, but at least the scanner found the board! So I'm assuming there's a design flaw in the nano clones. They've worked fine for everything else, but I2C seems to have been left out. FWIW, the nanos used a chip labelled Atmel Mega328P, and the uno had an Atmel ATMega328P-PU. Doesn't mean anything to me, but might to some of you. I'm going to try one more time tomorrow, with a uno and a servo controller with nothing but the wires shown in the Adafruit manual. I'll post the results. If it doesn't work I'll just break the task down to subunits and use multiple nanos running the software servo control. If it does, I've got a lot more head scratching to do :-). Again, thanks for the scanner code - at least I know a little more than I did before.