Fault route
CT-312 MMA Works but TIG/Plasma Fail Diagnostic
A mode-comparison route for CT-312 combo welders where MMA works but TIG or plasma does not.
Quick Answer
MMA working is strong evidence that the main inverter and basic output path can work. Start with mode switch, torch input, gas/HF support and process-specific control instead of replacing power devices.
Diagnostic path
MMA output works → mode switch → torch/gas support → HF/pilot start → process-control layer.
Evidence table
MMA works: shared output likely healthy. TIG no gas/HF: TIG support path. Plasma air works no arc: pilot/HF or transfer. TIG and plasma both fail: process-support control.