Disassemble the radio using the Exploded View (remove the volume knob, hex nut, and slide the chassis out). Step 2: Locate the Audio PA section on the schematic. Look for C621 and C622 (470uF/16V). These are the main audio coupling caps. Step 3: Using the Parts List , confirm the physical dimensions (6.3mm x 7.7mm) to ensure your replacement fits under the shield can. Note: The manual explicitly warns: "Do not use standard flux. Use no-clean flux only to prevent micro-leakage."
Low audio volume, humming in receive, or intermittent TX. Manual Reference: Section 6.1 (Replacement Procedures) & Parts List page 112. Motorola Gm3688 Service Manual