SDRPlay "miniSDR" clone repair

A clone of SDRPlay radio has been obtained from a shady Chinese seller.

Upon connecting, the device was completely dead (no activity on USB).

Dissection revealed the device contains:

• msi-2500 (USB, ADC and SPI bridge)
• msi001 (RF frontend)
• 42641 (RF switch)

The voltages on MSi-2500 were measured and USB connection was checked. Then the oscillator input was measured and found to be dead. The oscillator has input voltage not connected. After connecting the oscillator power pin and the +3V rail on the board (the connection displayed as red line in the picture), the device enumerates and sends us samples.

The tuner features 4 signal inputs and the RF switches need to be set correctly, otherwise pretty no signal is received. Unfortunately, Gqrx does not do this by default (at least with our configuration), which can be tested by tapping the signal testpoints (shown in yellow frame in the picture) and observing the spectrum (the VHF one is the one on the bottom).

The kernel SDR API sets these switches correctly, at least when tested on FM broadcast.