Preserve the symptom before choosing a part
A useful maintenance dossier contains the original alarm text, controller time, task stage, tool state and the changes already attempted. Distinguish operator recollection from an exported device log. Keep both, but label their origins. If the fault is cleared before collection, say so instead of reconstructing a precise timeline from memory. The purpose is to help a service party reproduce the decision path. It is not to make the first suspected component look certain. Photographs should identify a label or connection, not substitute for an electrical or mechanical inspection.
Build a compatibility map with separate decisions
Give mechanical mounting, power and pinout, feedback, control support, firmware and parameters their own rows. Each row should identify an original document, revision, confirming party and unresolved condition. A statement that two parts fit the same bracket does not answer whether the controller supports the feedback. Likewise, a matching protocol name does not establish the same object definitions or operating mode. Do not collapse the map into one green compatibility tick. A documented unknown is a more useful result than a substitute recommended without the evidence needed to inspect it.
Use a controlled comparison instead of several simultaneous changes
In a hypothetical fault investigation, a harness, drive and parameter set are all changed together and the alarm disappears. The observation supports only the new combination under the observed conditions. It cannot identify which change removed the symptom. Where the equipment procedure permits, record one authorised change at a time and preserve the task conditions. Where isolation is not possible, state the limitation. Never suggest bypassing a safeguard, feedback check or protection limit to make the comparison easier. A diagnostic record should retain unsuccessful and interrupted attempts as well as successes.
Match the observation window to the original condition
Suppose a hypothetical alarm normally occurs after an hour of ordinary operation, while the replacement was observed for ten minutes. The correct statement is that the alarm did not recur during those ten minutes, not that the fault was permanently fixed. Arrange further checks only within the device maker permitted operating conditions. State the tool, load, motion and environmental context. The service documentation used as a reference contains device-specific backup and software restrictions; it is not permission to restore an arbitrary controller image. [S2] An existing backup should be checked for identity and coverage before use.
Prepare a shipment and service handover record
The handover should include the robot identity, original and proposed part numbers, revisions, drawing references, configuration backup scope, packaging instructions from the responsible party, and the inspection expected on receipt. Add the approved return or disposal arrangement for the removed item. Keep commercial terms and technical confirmation distinct: a quotation does not establish compatibility or remaining life. For a gearbox, preserve the exact measurement definition rather than relabelling a loaded torsion number as backlash. The manufacturer catalogue supports that terminology distinction only within its stated families. [S1]
Close the enquiry at the level actually supported
A closure record should separately state the observed symptom, the change made, the task used for verification and the remaining uncertainty. Name the responsible roles and the documents needed to resolve open items. Do not invent a supplier authorisation, an inspection result or a warranty that has not been supplied. This site provides original sourcing and documentation guidance, not a live stock catalogue or a report of repairs performed. The worked arithmetic and hypothetical exercises illustrate reasoning; neither creates a performance specification for a product offered by this site.
References and scope
[S1] Harmonic Drive Engineering Data — Harmonic Drive LLC
https://www.harmonicdrive.net/_hd/content/documents1/FBB_DifferentialGear.pdf
Supports: Gear terminology including hysteresis and torsional stiffness.
Scope: Specific catalogue families; not unknown gearbox ratings or remaining life.
Checked: 2026-11-04
[S2] UR-Series Service Manual — Universal Robots
https://www.universal-robots.com/manuals/EN/PDF/Shared/service-manual_ur-series/Service_Manual_UR-Series_en.pdf
Supports: Device-specific backup and software restoration restrictions.
Scope: Use the applicable robot and software instructions; not a universal replacement approval.
Checked: 2026-11-04
Original editorial guide. Worked numbers are explicitly stated assumptions, not product specifications or measurements. Source documents retain their own scope; no claim of supplier affiliation or independent expert certification. Corrections: zhilianhai@t-800.cn.