A Dynapath Delta 20 installation with an SD1525-10 servo drive shows excessive Y-axis lag, growling during pendant jogging, and occasional program stops in which the control waits for the in-position signal without reporting an alarm or drive trip. Diagnose the drive response by applying the manual-specified small step command and observing tachometer feedback. Do not assume a test-point number or command-input pinout until the SD1525-10 documentation confirms it.
Separate the Symptoms From the Test Method
| Observed condition | What it establishes | What remains unknown |
|---|---|---|
| Lag exceeds the documented target | The Y axis is not following its command within the expected error | Whether the cause is tuning, motor condition, tachometer feedback, or the command signal |
| Motor growls during fine pendant jogging | The axis response is abnormal at low commanded motion | Whether the disturbance is electrical, mechanical, or adjustment-related |
| Program stops while waiting for in-position | The axis has not satisfied the control's position-complete condition | The evidence provides no applicable alarm code or threshold |
| No alarm or drive trip occurs | The stop is not accompanied by a reported fault | This does not prove that the drive, motor, or feedback is healthy |
Use the Tachometer Signal for Response Tuning
The cited drive-manual procedure calls for applying a small step input and observing the tachometer output on an oscilloscope as the motor stops. This waveform represents motor-speed response and can be compared with the response shapes and corrections in the applicable drive manual.
TP6 is identified as the tachometer test point in one referenced manual, but the evidence does not establish that every SD1525-10 uses the same assignment. Confirm the tachometer test point and its signal common in the exact drive documentation before connecting the probe. Do not substitute a motor-voltage node merely because the original symptom concerns motor behavior.
Choose a Controlled Step Command
A fine pendant jog was proposed as the excitation, but the evidence does not confirm that it produces the distinct, stable step required by the tuning procedure. First scope the drive command input, using the documented signal common, to determine whether the chosen command has a clean step shape and lasts long enough to expose the response described in the manual.
An external battery command was also proposed: a 1 to 5 kOhm resistor between the command input and signal common for a zero command, followed by a momentary battery connection. The reported pin assignments—pin 2 for command and pin 4 for common—belonged to another installation and must not be transferred to the SD1525-10 without schematic confirmation. A 9 V source can demand rapid acceleration; a 1.5 V cell was suggested as a lower-command alternative, but neither voltage is established here as an SD1525-10-approved test level. Use only the command magnitude, polarity, current-limiting arrangement, and connection points authorized by the drive manual.
Run the Scope Test Safely
- Review the SD1525-10 manual and machine schematics. Identify the documented command input, command common, tachometer test point, allowable step magnitude, and tuning controls.
- Position the Y axis with sufficient travel in both directions. A step can command motion in either direction according to polarity, so keep the emergency stop immediately accessible.
- Connect the oscilloscope probe to the confirmed tachometer test point and its documented reference. An isolation transformer does not replace verification of probe-reference voltage and test-point suitability.
- Apply only the manual-specified small, momentary step. Do not latch or clip an external source into a sustained command unless the documented procedure explicitly requires it.
- Capture the tachometer waveform through acceleration and the stopping response, then compare its rise, decay, and stability with the SD1525-10 manual.
- Make only the adjustment identified by the manual for the observed waveform, repeat the same test, and retain before-and-after captures.
Check Hardware Before Declaring a Tuning Fault
Inspect the motor brushes and tachometer as possible contributors before compensating with drive adjustments. Coolant exposure was suspected at the Y-axis motor, but the evidence does not confirm contamination as the root cause. Treat it as an inspection item, not a diagnosis.
Tachometer wiring was described as very fine. Avoid disturbing or repairing it without the applicable service procedure. If inspection finds contamination, damaged conductors, worn brushes, or unstable tachometer feedback, correct that hardware condition before final tuning; otherwise an adjustment may mask the defect.
Verify the Repair
Repeat the identical step test and confirm that the tachometer trace now matches the acceptable response in the drive manual without sustained oscillation or abnormal stopping behavior. Then test normal pendant jogging and programmed motion. The repair is complete only when Y-axis lag meets the machine documentation, growling is absent, and repeated moves satisfy the in-position condition without an unexplained stop.
The Delta 20 lag display was reported as available through Mode Select > Setup > TM4 Lag Display, but the evidence does not confirm availability on every software configuration. If that menu exists on the machine, use it to record lag before and after tuning rather than treating scope shape alone as acceptance.
FAQ
Where do I connect a scope when tuning a Dynapath Delta 20 Y axis?
Connect to the tachometer-output test point and its documented reference on the servo drive. TP6 appears in the referenced procedure, but verify that designation in the SD1525-10 manual before probing.
Can I use the Delta 20 pendant jog as the servo step input?
Only if a scope confirms that the drive input receives the clean, distinct step required by the tuning procedure. The evidence does not establish that the 0.0001 pendant setting produces a suitable calibration signal.
Why does the Y axis stop without an alarm while waiting for in-position?
The control has not received a satisfactory in-position result, while no reported alarm or drive trip identifies the cause. Capture the command and tachometer response, then inspect brushes, tachometer feedback, and wiring before changing the documented tuning adjustments.