Cummins/Onan — Sine wave filter troubleshooting
Testing & diagnosis
From a Cummins/Onan owner's manual — check it applies to your exact model before use.
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Before you start
- DON'T ATTEMPT TO DISASSEMBLE THE FILTER - ALL COMPONENTS MUST BE REPLACED IN MATCHED SETS.
Procedure
- Check the output wave with an oscilloscope.
- Remove all connections from the filter and measure resistance between terminals IN and C. After the capacitors charge, reading should be at least 1 megohm.
- Measure resistance between terminals OUT and C. Correct resistance is about 0.6 ohms.
- Measure resistance from C and IN to the chassis. If either shows a reading, it indicates a short to the chassis.
- If any test indicates the filter is defective, return it to the factory for repair. Don't attempt to disassemble the filter.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- IN to C at least 1 megohm
- OUT to C about 0.6 ohms
- C and IN to chassis no reading
Source: Cummins/Onan owner's 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.