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**Question:** Our servo press motor is making noise and we are getting intermittent encoder alarms. The motor is 8 years old. Repair shop quoted $4,000 to rewind and replace bearings. A new motor is $12,000. How do we decide?
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**Answer:**
Here is a framework to make this decision rationally.
## Assess the Motor Condition First
Before deciding repair vs. replace, get a full condition assessment:
1. **Insulation resistance**: measure with a megohmmeter at 500V.
- Above 100 megaohm = good
- 10-100 megaohm = marginal
- Below 10 megaohm = replace
2. **Winding resistance balance**: measure resistance between each phase pair. Should be within 2% of each other. Imbalance above 5% indicates winding damage.
3. **Bearing condition**: with the motor uncoupled, spin the shaft by hand. Rough or gritty = replace bearings.
4. **Encoder condition**: intermittent encoder alarms - check the encoder cable first (most common cause). If the cable is good, the encoder itself may be failing.
## The Decision Framework
**Repair makes sense when:**
- Insulation resistance is above 50 megaohm (winding is fundamentally sound)
- The failure is isolated (bearings only, or encoder only)
- The motor is a non-standard frame size that is hard to replace
- Lead time for a new motor is 12+ weeks
**Replace makes sense when:**
- Insulation resistance is below 50 megaohm
- Multiple failures at once (bearings + encoder + winding issues)
- The motor is 10+ years old and has been repaired before
- New motor comes with 2-year warranty vs. 6-month on repair
## For Your Specific Situation
8 years old with noise and encoder alarms: get the insulation resistance test done first. If above 50 megaohm, the $4,000 repair is reasonable. If below 50 megaohm, the winding is degraded and you will be back for another repair in 1-2 years - spend the $12,000 now.
## Total Cost of Ownership
- Repair: $4,000 now, likely another repair in 3-4 years ($4,000-$6,000), then replacement. Total over 8 years: $10,000-$14,000.
- Replace now: $12,000 now, likely good for 10+ years. Total over 8 years: $12,000.
The numbers are close. The insulation resistance test result is the deciding factor.