Cummins/Onan — Loss of Welding Power Troubleshooting
Testing & diagnosis · Generator / control box
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Do not perform troubleshooting tests with the generator running.
Procedure
- Remove control box cover screws and lift off cover.
- Visually check rotary switch wiper blade and contact points for burned areas.
- Check switch contact resistance with ohmmeter; low reading less than 2 ohms is good.
- Examine all leads, terminals and screw connections for opens or shorts.
- Isolate diode and check with ohmmeter by reversing leads.
- Isolate small resistor and test; resistance should measure 2.7 ohms +/- 5%.
- Remove end bell cover and fan; check brushes and all connections.
- If power loss only in upper ampere ranges, substitute known-good electrolytic capacitors.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Switch contact resistance less than 2 ohms
- Resistor 2.7 ohms +/- 5%
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.