Symptom: Low RX sensitivity on 2-meters.
Probable Cause: Burned D6 on PA unit.
Cure: Replace D6 (MA862).
Symptom: No TX power output on an HF band.
Probable Cause: Bad filter relay.
Cure: Locate and replace faulty filter relay (will be type AHY-103).
Symptom: Low/distorted RX audio.
Probable Cause: Burned foil trace on PLL unit.
Cure: Repair SPE (ground) foil trace on PLL unit.
Symptom: Low TX output on HF & 6-meters.
Probable Cause: Shorted D18 and Q1 in filter unit.
Cure: Replace D18 (DAP222) and Q1(2SC4081).
Symptom: Inadequate mic gain.
Cure: Install field mod on main unit: Change value of R236 from 27k, to 68k-82k. [The higher the resistor value, the greater increase in mic gain].
Symptom: Thin-sounding mic audio.
Cure: Install field mod inside HM-103: Remove rubber gasket from beneath mic element.
Symptom: Off frequency in FM TX.
Probable Cause: FM VCO lock voltage needs adjustment.
Cure: Adjust FM VCO lock voltage for 1.5 volts as per service manual.
Symptom: Unit is stuck in TX mode.
Probable Cause: Shorted T/R switch transistor.
Cure: Replace shorted Q32 in main unit.
Symptom: Radio won’t power up.
Probable Cause: Burned ground foil trace in flex cable.
Cure: Replace flex cable EP2 at main board.