Emergency: same day
For a line-down motor, where the fault and parts allow. WhatsApp us before you send it so the bench is kept free.
Resolver repair · Test and align
Servo motor resolver repair and alignment
A resolver is a rotary transformer: an excitation signal goes in, and sine and cosine signals come out in proportion to the shaft angle. It has no electronics inside, so it survives heat and vibration well, but windings open, insulation breaks down, cables fail and the stator can slip. We test resolvers electrically and in motion, repair or replace them, and align them to the rotor.
Repair turnaround you can plan around
Send a photo of the nameplate first. We confirm whether the motor is repairable, and the quote, the same working day.
Urgent: 3 working days
Repair, encoder alignment and test, counted from the day the motor reaches the bench and the quote is approved.
Standard: 7 working days
Full repair, encoder alignment, run test under load and a printed test report.
- Free repairability check from a nameplate photo
- Printed test report with every motor
- Written warranty, terms stated on every quotation
- Pickup can be arranged; parts that must be imported are quoted with their own timeline
01Tests
How we test a resolver
| Test | What it shows |
|---|---|
| Winding resistance | Open or shorted excitation, sine or cosine winding |
| Insulation to frame | Breakdown that causes noise or earth faults |
| Excitation sweep | Excitation set between 1 and 20 kHz at 2 to 3 V, so the waveforms are clean and in phase |
| Vector level and ratio | Transformation ratio compared with known good units of the same type |
| Angle through a full turn | Linearity, dead spots and jumps |
| Speed (poles) | Single or multi-speed, matched to the motor |
| Lead direction | Sine and cosine connected for the correct direction of rotation |
02Faults
Common resolver faults
- Open winding after overheating or cable strain
- Insulation breakdown from coolant or oil ingress
- Stator slipped in its housing, so the commutation offset has moved
- Loose rotor on the shaft
- Broken or crushed feedback cable and connector pins
- Memory board faults on Bosch SR and Indramat MKD, MKE and MDD motors
03Motors
Resolver motors we repair
Allen-Bradley MPL and 1326AB, Bosch SR and Bosch resolver motors, Indramat MKD, MKE and MDD, Kollmorgen Goldline and Seidel 6SM, Parker HDY, HJ, CMP, MMP and MPJ, Baldor BSM and BE, SEW Eurodrive DFS, Lenze MDFK, Siemens resolver motors, Pacific Scientific and PMA, Moog G series, Baumüller DS, Elau SM, Servax MDD, Control Techniques Dutymax, Emerson and Custom Servo, Fanuc DC motors with resolver and tach.
04FAQ
Resolver questions
How do I know if a resolver has failed?
Typical signs are a feedback or resolver loss alarm, position jumps, a motor that runs rough at one point of every turn, or a winding that reads open or low to earth. A resistance and insulation check on the excitation, sine and cosine windings is the first test.
Can a resolver be rewound?
Sometimes, but the ratio and accuracy are hard to restore. We usually replace a failed resolver stator or rotor with a matching unit and then align it.
What is a two-speed resolver?
A resolver whose angle goes through 360 degrees twice per shaft turn. Multi-speed resolvers usually match the motor's pole pairs, for example a four-speed resolver on an eight-pole motor.
Why does my motor run backwards after a resolver change?
The sine leads are reversed. Swapping sine leads reverses the direction of the angle; swapping cosine leads reverses it and adds 180 degrees.
Free downloads for your maintenance file
Printable one-page sheets from our bench. More on the resources page.
Servo motor encoder quick reference
Encoder families, interfaces, counts per revolution and the motors they sit on: Fanuc pulsecoders (alpha A64, A1000), Mitsubishi OBA/OSA, Yaskawa UTOPH, Tamagawa, Heidenhain ECN/EQN/ERN and SICK SKS/SRS/SRM.
PDF · 2 pages · 8 KB · free, no sign-up
Download PDFEncoder alignment checklist
What to record before removing an encoder, the order of checks after refitting it, and the readings that tell you commutation is right before the motor goes back on the machine.
PDF · 1 page · 4 KB · free, no sign-up
Download PDF05Enquiry
Send the nameplate or encoder label
A clear photo of the motor nameplate and, if the cover is off, the encoder label is enough to start. We reply with whether it can be repaired and a quote.
Message received
Our team replies by email or WhatsApp, usually the same working day. For a line-down motor, WhatsApp +91 97866 22233.