I have not worked on a CR-1000, everything looks so crammed/inaccessable.
You could try a basic continuity check to rule out some of the switches.
Amp powered off/unplugged.
Input selector set to AUX-2, all other controls normal position, SOURCE etc...
Measure resistance from Left AUX-2 RCA (inside) to wires on volume pot in brown rap.
One should give OL (right channel) the other should not give OL, maybe kohms
depending on switch position. You can try same for Right AUX-2 RCA.
Can also try connecting source(CD-P?) to TAPE-PB-A and tape
monitor switch to PLAY A, this would bypass the input selector. Any audio?
The tone and filter amp use +B(50V) supply
The filter amp has a mute function (TR607,8).
Try measuring the dc voltage at the green wire on the power board as shown.
Near zero volts is good.