Although the following email is about a SoftRock V5, compare the schematic to your version as it addresses things in common to all receivers.

To:
From: "Tony Parks"
Subject: Re: [softrock40] Re: SRv5 - 1/2 actual soundcard bandwidth - confusion ?!?

Any place in the SoftRock circuit or connection to the soundcard that
seriously affects one of the audio channels will result in little or no
image rejection. This can include items on the OSC/BPF board, the QSD board
or even the soundcard input. Some things to check wold include the
following:

1. R25 and C25 values on each of the OSC/BPF boards.
In a number of cases the OSC/BPF kits were shipped with a 100k resistor for
R25 rather than the correct value of 1k. Measure the resistance between
pins 5 and 6 on the 15-pin header to make sure R25 is 1k. Read the value
code on C25 to be 151 (150pF) for 40m and 470 (47pF) for 20m.

2. Wiring on secondary of T21.
The resistance between pin 9 and 10 on the 15-pin header should read about
zero. Also the resistance between pins 9 and 11 should read about zero.
Along with the correct resistance readings the wires connected to via 6 and
via 3 on the T21 mounting position should come out of opposite side of the
T21 core, one out of the top and one out of the bottom.

3. If you have a scope then view the waveforms on pins 5 and 8 of the
15-pin header. Both should be fairly symmetic square waves with the
waveform on pin 8 lagging 90 degrees compared to the waveform on pin 5.
(Circuit ground is at pin 12 of the header.)

4. The DC voltage at pin 9 of the 15-pin header should be close to 2.5 VDC.

5. The DC voltage at the + wire on C13 and C14 should both be close to 2.5
VDC.

6. Make sure you really are plugged into the line-in on your soundcard and
the soundcard is selected by the SDR program in use.

Hope the above make sense and will help a bit.

73,
Tony KB9YIG