开云体育

How did you determine that the outputs of IC405 and IC406 are OK?

Is IC407 getting warmer than you would expect? You can assess its current draw from Vcc by measuring the voltage drop across the inductor that is in line with Vcc. It should have a resistance of about 1.5 ohms. Excessive current draw vs. spec would indicate a problem. Nominal current draw (about 35 mA) remains inconclusive.

No signal at pin 1 of IC401? Yes, that is worrisome. That I2S audio digital data signal must pass through the MCU though. If you are willing to put up with some PC SW setup hassles, here is a way to see IC407? output activity somewhat more directly:

The program HDSDR allows you to set QMX into IQ mode and to listen to/observe the I and Q channels more directly, with simple conveyance of raw digital data to the USB port, no down conversion or detection processes in play at the MCU. Other SDR programs may also allow independent checks on the I and Q channels.

It is possible, by carefully soldering fine wires to the leads of IC407, to see the digital output data absolutely directly from the ADC chip on a scope screen.

The signal LRCK is a frame sync clock that divides the data output channel into Left and Right time slices. Use it as a sync source for the scope. Monitor DATA/DSDR on a second scope channel.

By tuning through a constant carrier, especially as you go through a near zero beat condition, you should be able to see the digital data responding. I have done this and successfully observed the failure of one ADC channel.

I hope you find some value in all that ...