Cummins/Onan — Checking rectifiers (Step 1)
Testing & diagnosis · Magneciter rectifiers
From a Cummins/Onan service manual covering: 10.0JC, 12.5JC, 15.0JC, 4.0JB, 5.0JB, 6.0JB, 6.1JB, 7.5JB, 7.6JB. Check it applies to your exact model before use.
Applies to: Cummins/Onan 10.0JC, Cummins/Onan 12.5JC, Cummins/Onan 15.0JC, Cummins/Onan 5.0JB, Cummins/Onan 6.0JB, Cummins/Onan 6.1JB, Cummins/Onan 7.5JB, Cummins/Onan 7.6JB, Cummins/Onan JB engine, Cummins/Onan JC engine
Before you start
- Note carefully the direction of mounting of any rectifier removed; it must be re-mounted in its original direction
Procedure
- Disconnect one lead from, or remove, each rectifier for its individual test
- Connect the ohmmeter across the rectifier contacts and observe the meter reading
- Reverse the connections and compare the new reading with the first reading
- If one reading is considerably higher than the other, the rectifier is satisfactory
- If both readings are low or both indicate open circuit, replace the rectifier with a new identical part
Tools required
- ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Full service-parts list: Cummins/Onan 10.0JC →, Cummins/Onan 12.5JC →, Cummins/Onan 15.0JC →, Cummins/Onan 5.0JB →, Cummins/Onan 6.0JB →, Cummins/Onan 6.1JB →, Cummins/Onan 7.5JB →, Cummins/Onan 7.6JB →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.