Yamaha YZF-R125 Service Manual: Checking the rectifier/regulator

1. Check:

Rectifier/regulator output voltage Out of specification → Replace the rectifier/ regulator.


a. Set the engine tachometer to the spark plug lead.

b. Connect the pocket tester (DC 20 V) to the rectifier/regulator coupler as shown.


  • Positive tester probe
    red "1"
  • Negative tester probe
    black "2"

Checking the rectifier/regulator


c. Start the engine and let it run at approximately 5000 r/min.

d. Measure the charging voltage.

    Checking the stator coil
    1. Disconnect: Stator coil coupler (from the wire harness) 2. Check: Stator coil resistance Out of specification → Replace the crankshaft position sensor/stator assembly. a. Conne ...

    Checking the horn
    1. Check: Horn resistance Out of specification Replace. a. Disconnect the horn connectors from the horn terminals. b. Connect the pocket tester ( × 1) to the horn terminals. Positiv ...

    Other materials:

    Disassembling the rear brake caliper
    1. Remove: Brake caliper piston "1" Brake caliper piston dust seal "2" Brake caliper piston seal "3" a. Blow compressed air into the brake hose joint opening "a" to force out the piston from the brake caliper. WARNING Cover the brake caliper piston with a rag. Be careful no ...

    Checking the crankshaft position sensor
    1. Disconnect: Crankshaft position sensor coupler (from the wire harness) 2. Check: Crankshaft position sensor resistance Out of specification  Replace the crankshaft position sensor/stator assembly. a. Connect the pocket tester ( × 100) to the crankshaft position sensor c ...

    Faulty lighting or signaling system
    Headlight does not come on - Wrong headlight bulb - Too many electrical accessories - Hard charging - Incorrect connection - Improperly grounded circuit - Poor contacts (main or light switch) - Burnt-out headlight bulb Headlight bulb burnt out - Wrong headlight bulb - Faulty battery - Fau ...

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