Basic Diagnostics for Testing AC Output

Updated by Juan Velez

This coves the following Champion Power Equipment models: 79cc - 439cc Engine Powered Generators.

Read instructions carefully and completely before performing service.

  • To reduce the risk of injury, user must read and understand the operator’s manual before using this product.
  • DO NOT make any adjustments to the generator without first stopping the engine and disconnecting the spark plug wire.
  • Burns from hot parts — let the engine cool completely before touching hot parts.
  • Injury from moving parts
  • To reduce the possibility of fire or explosion, be careful when working around gasoline. Keep cigarettes, sparks and flames away from all fuel‐related parts.
  1. Remove the two 7mm bolts in the yellow end on the generator end.
  2. Locate the AVR (Automatic Voltage Regulator) at the 7 o'clock position. (Silver curved aluminum device; brush assembly at 11 o'clock and the terminal block at the 4 o'clock position.)
  3. Identify the terminal block connections as one through four from high to low.
  4. Test the brushes for DC power excitement by removing either wire from the brush holder and scratching it against its connection to notice a bright blue spark. This is only 12 volts DC so there is no danger or electrical shock. (Flash test.)
  5. If no spark appears, then remove the brush assembly and check for damage. (i.e.: burnt contacts, broken carbon brushes, or any other physical damage that is evident.) Remove the brush assembly and inspect it for any damage, reinstall it, and repeat the flash test for spark. If a spark does appear, reinstall the terminal and check for voltage output at meter.
  6. If no spark appears, then excite the brushes with an external 12 volt power source. If this produces panel voltage on the volt meter, then the stator and rotor are initially OK and a replacement of the AVR is necessary. If replacing the VR does not correct this matter, it is possible that the exciter winding is defective and not producing satisfactory AC excitement to the regulator rectifier (AVR) that will convert this signal to a DC voltage for the brushes. A complete stator replacement would now be required.
  7. If there is still no voltage, it is time to check the rotor for continuity. Remove the brush holder and, using a continuity tester, touch each of the slip rings that contact the brushes for continuity. The tester should be giving you a closed test or continuity. If you have no continuity between the slip rings on the rotor, check to see if there is a broken wire at the connection between the stator and the slip rings. You can see the connections with the brushes removed.
  8. Test the AC output at the terminal block by attaching your voltage multimeter at the terminal block between connections 1 and 2, 2 and 3 (3 and 4 on the 4-wire connections). Both of these tests should show 115-125 volts. If either test is low, then you probably have a defective stator. If the voltage is good at these connections, then you must check all the wiring between the terminal block and the panel for poor or broken connections.
  9. The hot leads will normally be brown or blue (120V). The neutral or common will usually be white in color. If all voltage is lost after plugging in an outside load, then the neutral wire has a poor connection in its circuit. If you only lose one winding's output, then the brown or blue wires will possibly have a broken connection in its circuit; a stator replacement will be needed.

View and download the PDF version here.

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