Inspect the inline fuse on the DC power cable. Check the DC power connector pins for corrosion or spreading. Measure the voltage at the main power switch transistor on the board; it should read close to the supply voltage (13.8V). Transmitter Faults Symptom: Low RF output power or no transmission.
The is an essential technical resource for maintaining and repairing this alphanumeric display mobile radio. It provides qualified technicians with the information needed for component-level troubleshooting and repair. Manual Content Overview motorola xir m3688 service manual
What (e.g., service monitor, wattage meter, tuner software) do you have available at your workbench? Inspect the inline fuse on the DC power cable