Motorola Xir M3688 Service Manual -

Motorola XIR M3688 VHF/UHF Mobile Radio Service Manual Report

Document Number: 6881099E95 (based on GM/CM/M series platform)
Revision: R01
Date: April 2026
Classification: Service & Maintenance (Level 2 & 3)

3. Theory of Operation (Simplified)

The XIR M3688 uses a dual-conversion superheterodyne receiver and a direct FM transmitter. motorola xir m3688 service manual

4.2 Opening the Radio

1. Remove the two T10 screws from the rear heatsink.
2. Slide the front panel upward by 5 mm, then pull forward.
3. Disconnect the flex cable connecting front PCB (keypad/LCD) to main board.
4. Remove the main PCB by unscrewing four cross-head screws from the chassis.
5. The RF power module (heatsink-mounted) can now be accessed.

Caution: The PA module is ESD sensitive. Ground yourself before handling. Motorola XIR M3688 VHF/UHF Mobile Radio Service Manual

5. Alignment Procedure (Without Test Box)

Note: Full alignment requires Motorola RIB (Radio Interface Box) and CPS. The following is a summary of factory adjustments. Remove the two T10 screws from the rear heatsink

2. Technical Specifications

| Parameter | VHF | UHF | |-----------|-----|-----| | Frequency stability | ±2.5 ppm (-30°C to +60°C) | ±2.5 ppm | | Modulation | 11K0F3E (25 kHz), 8K50F3E (12.5 kHz) | Same | | Conducted spurious | -36 dBm (<1 GHz), -30 dBm (>1 GHz) | Same | | Audio output (internal speaker) | 4W @ 4Ω, <5% THD | Same | | Supply voltage | 13.8V DC ±20% (10.8–15.6V) | Same | | Current drain (standby) | <0.5A | <0.5A | | Current drain (transmit) | 11A @ 45W | 10A @ 40W |

Safety and Compliance

• Electrical safety: Disconnect battery and antenna before servicing. Avoid conductive tools contacting circuitry. Use insulated ESD-safe tools.
• ESD precautions: Wear an ESD wrist strap, use grounded mats, and handle PCBs by edges.
• Battery handling: Use manufacturer-specified batteries; replace only with compatible cells; recycle per regulations.
• RF exposure: Do not transmit with the radio held against your body except with an approved accessory. Maintain manufacturer-specified separation distances.
• Regulatory labels: Preserve FCC/CE markings and serial number labels; record IMEI/ESN/serial before service.