JPXI-7 MAG TONE knob doesn't work in stereo output

Hi! I bought used guitar JPXI-7 The guitar was with another pickup in bridge “D ACTIVATOR” I returned “CRUNCH LAB”. MAG TONE knob doesn’t work in stereo output with mono jack (seems like low pass – sounds deaf) but works fine in mono output. Coil split works fine in both outputs. How can I solve this issue soldering pickups? You could send me the correct diagram electronics – soldering pickups? For JPXI-7???