Mitsubishi MDS alarm 37 means an initial parameter error — an incorrect parameter was detected among those the drive received from the CNC at power ON. The drive refuses to start on data it cannot accept — the Mitsubishi equivalent of Fanuc's AL-34, and like it, this alarm virtually never appears on an untouched machine: it follows parameter edits, restores, drive swaps or commissioning. The good news: the NC diagnosis screen displays WHICH parameter is in error — the hunt is a lookup.
Step 1 — Servo axis or spindle?
Determines the parameter range to inspect: servo → SV001–SV065, SV082; spindle → SP001–SP240.
Step 2 — Servo: read the error parameter on the NC diagnosis screen
Mitsubishi lists the specific cases worth knowing:
- A value outside its designated range → correct it — from the machine's documented backup, never a guess.
- The electronic gears are overflowing: the combination of SV001 (PC1), SV002 (PC2) and SV018 (PIT) produces an internal ratio the drive cannot compute — set them to match the actual machine specification (gear teeth and ballscrew pitch), not values that merely look plausible.
- Absolute position parameter enabled without the option: absolute position detection is configured but the system (OSE104/OSE105 encoder connection context) has no absolute position option → either the option is required, or the parameter must be returned to incremental.
- SV082 bits C–F consistency: the function selections in SV082's upper bits must be set consistently — the manual flags both variants: the same setting where difference is required (correct bits 0–B accordingly) and different settings within one unit where they must match (make them the same). On 2-axis drive units, both axes' settings must agree.
Step 3 — Spindle: SP001–SP240
- Out-of-range value → correct it within the designated range.
- Values correct in range but different from what the machine's specified encoder requires → change the setting to meet the machine specification — the classic case after a spindle motor/encoder substitution: the parameters must describe the encoder actually fitted.
Step 4 — Still refusing? Work the alarm 34 items
Mitsubishi routes persistent cases to the alarm 34 (initial communication) checks — if corrected parameters won't take, the CNC-to-drive data path itself is suspect.
Diagnosis checklist (in order)
- Read the error parameter number on the NC diagnosis screen.
- Servo → check range, electronic-gear overflow (SV001/SV002/SV018), absolute-position option, SV082 consistency.
- Spindle → check range and encoder-specification match (SP001–SP240).
- Correct from documented values; power cycle.
- Persists → alarm 34 communication checks.
Related guides
- Mitsubishi M70/M80 parameter backup guide
- Mitsubishi MDS alarm 31 (overspeed — the same parameter family)
- Mitsubishi M70/M80 alarm list