dirt: "avrdude: initialization failed, rc=-1"

Other Hardware General Electronics
1

I've been suspecting my often flaky USBtinyISP of causing me headaches with a project. But today it would communicate with the processor for about 15 seconds after connecting it and then I'd get the "initialization failed" message until I unplugged everything and let it sit for a while. What could that mean?

I eventually figured out that the CS pin of the lone SPI device was dropping to ~1V when reset was applied. The device has an integral 70kΩ pull-up resistor. Could it have been damaged somehow? That seemed unlikely.

Long story short, it was dirt. Some sort of goo, possibly remnants of the adhesive on some electrical tape I used to insulate the board from nearby components. You can see it in this photo: a thin strand of black gunk bridging between the ground pin (top) and the CS pin next to it. It was like a pull-down resistor.

I guess the electrical tape was a bad idea.

2

If the tape absorbs moisture from the air, it becomes a plausible conductor. Clean with IPA and dry
thoroughly?

3

Yes, cleaned with IPA and blow dried and everything is as it should be again.

My USBtinyASP still flakes out unpredictably from time to time though. I should probably buy something else as a backup for when it's acting up.