Working on a simple I2C setup: Raspberry Pi connected to a WM8731 audio chip. The Raspberry Pi configures the WM8731 (which is write only) over I2C.
Problem is WM8731 doesn't always respond with ACK. I have logic analyzer attached to the I2C lines, and about 5% of the time the transmissions end in NAK. No other devices are on the bus.
The curious thing is when I attach oscilloscope probes to the lines, it greatly increases the number of NAKs. The scope shows nice sharp transitions on SDA and SCL, but sometimes the WM8731 just doesn't pull low for ACK.
What could be going on such that merely attaching the scope probes would make the problem worse?
Signals during proper transmission:
Signals during NAK: