Trouble Shooting for Field Excited Charging Systems

Charing Systems Failure Trouble Shooting Tips

Professional advice about trouble shooting charging system failure on Honda and Yamaha engines by Rick’s Motorsport Electrics.

Instructions for Honda and Yamaha Engines

Honda CB650 Year / Make / Model: 1979-1983 Honda CB650/750/900/1000

Yamaha XJ550 Year / Make / Model: 1980-1983 Yamaha XJ550/650/750 & 1975-83 XS650

What Causes Rotor Failure?

When charging failure occurs, it is most often the rotor. Heat and vibration break down the insulation on the copper wire inside the rotor resulting in a “short” of the current from one coil to the next. This prevents the electro-magnet rotor from providing sufficient magnetic strength to produce a strong charge in the stator. A secondary problem may now surface. When the internal rotor “short” occurs, the resistance in the rotor goes down and current flow increases. This puts a heavy load on the rectifier/regulator and may burn out the regulator unit. When the rotor fails, always replace the rectifier/regulator.

How To Test a Rotor

  • Clean a spot on each of the 2 slip rings
  • Set a digital OHMs meter to 0-20 OHMs
  • Put one probe on one ring, and one on the other
  • Record the OHM reading

An “open” reading or low reading of 1 OHM or less is bad. A good rotor reads 4-6 OHMs. A reading between this indicates a questionable rotor & the decision to replace it should be
made by the technician.

  • Now test from any one ring to the steel base (A good rotor should have NO continuity)

If your rotor tests good – test the stator

  • Identify the 3 stator wires (probably all yellow)
  • Check all 3 wires for continuity (approximately. .5 – 1 OHM)
  • There should be no continuity to ground

There is no field test for the rectifier/regulator, however we can test your unit at our facility.

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