Motorola MC Micro Audio Modification
Cut the left jumper (JU602) and solder together the right jumper (JU601) for FLAT audio
Change the three resistors (R614 – 33kOhm, R615 – 100kOhm and R616 – 100kOhm) to half the value: ~15kOhm, 47kOhm, 47kOhm.
Change capacitor C608 – 33nF to 1nF:
Solder a 10uF electrolytic from pin 4 of U551 to pin 3 of the DB15 connector (cut pin 3 and change from the original audio output to this).