Transmit audio drops to zero after many transmit cycles

[KI3P]

After several hundred PTT presses, the level of the transmit audio drops off substantially. I've traced the issue down to the microphone samples: the samples being read from the microphone drop in amplitude. The amplitudes recover if you speak very loudly / turn up the signal level and then drop if back to its original level. This implies some strange state in the DSP on the Teensy audio hat's SGTL5000 chip.

Next step: examine the I2S samples with a logic analyzer to confirm that the data issues are on the Teensy audio hat.

[KI3P]

I ran a test where I engaged PTT for 1 second and measured the RMS of the I/Q outputs from the main board to the RF board. The input to the microphone was a 20mV amplitude sine wave at 1 kHz. I repeated this 500 times and did not see a drop in the transmit amplitude.

I repeated it 100 times with the PTT engaged for 10 seconds. Same outcome.

I repeated it 100 times with the PTT engaged for 30 seconds. Same outcome.

Going to wait for it to naturally reoccur and standby with I2S probes.