Replacing a Discontinued Servo Drive on a Legacy Machine: What Has to Match the Motor, Encoder, Brake, and Cable

Replacing a Discontinued Servo Drive on a Legacy Machine

We are an independent industrial automation distributor and a China-based sourcing desk. The inquiry we receive most often is not "where can I buy this servo drive" but "the drive is no longer manufactured — can you find a drive that will still run my motor". The honest answer depends on four motor-side points. By aoctrl sourcing desk. Data through: September 2026. The drive can be replaced; the pairing cannot. Below is the way we read a servo motor's nameplate, the encoder protocol it carries, and the brake wiring inside its junction box before we will quote a substitute drive.

Why a servo drive is harder to replace than a contactor

A contactor is a passive device: it closes on a coil signal, opens when the coil is de-energised, and the contactor on either side of the swap only has to carry the same load. The control logic is outside the contactor. A servo system is different — the drive and the motor are a closed loop. The drive has to send a precise current waveform to the motor's windings; the motor's encoder sends position back to the drive at a high rate; the brake inside the motor, if present, has its own wiring and its own power supply; and the drive's commissioning software has to know how to map the encoder's resolution to the motor's torque constant. None of those five things are interchangeable.

This is why we refuse to substitute on a label match alone. We have seen buyers arrive with an inquiry that says "I have a Yaskawa Sigma-7 SGD7S drive on a 750 W application and the drive is obsolete — please quote a replacement", and the answer is not a part number, it is a verification pass on the motor side first. The drive can be swapped; the closed-loop pairing is what we have to verify.

The four motor-side questions we ask before any drive goes on the quote

The motor on the shaft is the contract. The drive has to honour it. Four points decide whether any drive — original-brand or third-party — will actually run the motor on the bench.

Encoder protocol and resolution

Every servo motor carries an encoder on the non-drive end of the shaft. The encoder reports position to the drive; the drive uses that position to close the current loop. The encoder protocol and the encoder resolution are not separate things — they are part of the motor's electrical identity. A drive that supports an incremental 17-bit encoder cannot read an absolute 23-bit encoder. A drive that supports EnDat 2.2 cannot read a BiSS-C encoder. A drive that supports a specific Yaskawa, Mitsubishi, Inovance, or Delta serial protocol will not read the motor's encoder if the protocol family does not match.

The encoder protocol is published in the motor's datasheet. The encoder resolution is published in the same datasheet. Both have to be confirmed against the candidate drive's datasheet. We treat this as the first axis — if the encoder does not read, nothing else matters. A drive that supports the wrong protocol will simply post a serial-communication fault on power-up and refuse to close the loop.

Winding rating and continuous / peak current

A servo motor's datasheet publishes its rated power, rated speed, rated torque, peak torque, and the torque constant Kt. The drive's continuous current rating has to be at least equal to the motor's continuous current; the drive's peak current has to be at least equal to the motor's peak current. A 750 W motor that needs 4.3 A continuous and 12.9 A peak cannot be driven by a drive rated at 3.5 A continuous and 8 A peak, even if the encoder protocol is correct — the motor will simply stall under load and the drive will trip on overload within seconds of the first acceleration.

A drive with significantly higher current rating can drive the motor, but the drive's tuning gains will need to be re-mapped; an oversized drive on a small motor is not "safer", it is just less stable and harder to commission. The right match is at or marginally above the motor's rated current, with the drive's overload envelope matching the motor's peak current.

Brake wiring and brake power supply

Many servo motors on machine tools, packaging lines, and indexing conveyors carry an electromagnetic brake on the back of the motor. The brake holds the shaft in position when the drive is de-energised. The brake has its own wiring — usually a 24 V DC coil — and the brake's power supply is typically taken from the drive's auxiliary output, not from the cabinet's 24 V rail. A replacement drive that does not expose a brake output on the same connector pin, or that requires a different brake supply voltage, will leave the motor unbraked on power-down. On a vertical axis that is a safety event.

We will not quote a drive that does not publish a brake output on its datasheet, and we will not quote one that publishes a brake output but assigns the brake pins to a different connector than the motor's junction box expects. The brake wiring belongs to the drive's connector pin map, and that pin map has to match what is already inside the motor's junction box.

Cable pinout and connector family

The cable that joins the drive to the motor is not a generic cable. Power conductors, brake conductors, and encoder conductors are bundled into specific connector families — typically M17 or M23 circular connectors on small-frame motors, and rectangular connectors or terminal boxes on larger frames. The connector family on the drive side, the pin assignment, and the wire cross-section all have to align. A third-party drive with a different connector family requires either a re-terminated cable, a motor junction box rewire, or a transition cable — and that transition cable is not always published by the drive vendor, which means it has to be sourced separately or built.

When we cannot find a published pinout-to-pinout mapping between the original drive's connector and the candidate drive's connector, we refuse the substitution. Building a transition cable in the field is not the same as quoting a drive; it is a separate work item that the buyer's electrical integrator should own.

Catalog anchor — what the Inovance side of the comparison actually looks like

The candidates we list on the report come from the Inovance IS620 and SV660 servo drive families, both of which are stocked in the catalogue. The IS620 family (IS620PS1R6I, IS620PS2R8I) is the legacy servo drive platform, sized for sub-3 kW applications and supporting Inovance's ISMV series motors with the Inovance serial encoder protocol. The SV660 family (SV660NT2R8I, SV660NS2R8I and the wider SV660NT / SV660NS / SV660NL ranges) is the next-generation platform, sized for the same sub-3 kW bracket but with the updated serial protocol and the broader tuning firmware. A same-brand move from an IS620 to an SV660 on the same Inovance motor is the lowest-friction path; a cross-brand move from a Yaskawa or Mitsubishi motor onto either IS620 or SV660 carries the encoder, brake and cable axes described above and is treated as a four-axis verification problem. Per-line condition is stated on every quote; per-line MOQ, lead time, and price are quoted per order.

What a cross-reference on a servo system actually reports

The output we deliver for a servo pairing question is a written comparison with each of the four points above marked as matched, differs, or unknown. We do not write that the candidate is a drop-in or that it is compatible with the existing motor — those claims are reserved for the original drive on the same motor. A replacement drive is, by definition, a candidate that has to be verified.

The format is one axis per row, with the original drive, the candidate drive, and a verdict. A typical report on a discontinued Yaskawa Sigma-7 SGD7S driver to an Inovance IS620 candidate looks like this:

The "differs" verdicts above are not rejections. They are the conditions under which the substitution can proceed — provided the buyer's engineering integrator is willing to (a) rewire the encoder, (b) accept that the candidate drive will derate the original motor on peak transients, and (c) build or buy a transition cable.

What we will not write into the report is that the candidate is drop-in on the existing motor. We will not write that it is compatible without re-engineering. We will not write that it is interchangeable without re-engineering, and we will not write a direct-replacement claim in any language — those claims overreach what the datasheets can prove. The report names what is matched, what differs, and what is unknown; the decision to substitute rests with the buyer's engineering team.

Where the desk will refuse to quote

There are three situations where we decline a servo drive substitution entirely:

1. The original motor is part of a fail-safe safety circuit (SIL/PL rated under IEC 61508 or ISO 13849). The motor's encoder is part of the safety chain; substituting the drive changes the safety case, and we do not make that call. The buyer's safety engineer must hold that decision and we name this on the report.

2. The original motor carries OEM firmware that locks the drive pairing. Some machine builders publish a drive that only commissions with their proprietary parameter set; the parameter set is keyed to the motor's serial number. A substitute drive will not commission on that motor even if the encoder reads. We name this on the report and decline.

3. The buyer's machine carries a third-party certification listing (CE Machinery Directive, UL 508A panel listing, or a regional listing in the destination market). Replacing the drive can break the listing. We name this on the report and refer the buyer back to the certifying body.

Outside those three cases the report is actionable. Inside them, the answer is "not from us".

Where the four motor-side axes cannot be reconciled without rewiring the encoder, derating the motor, and rebuilding the cable, the substitution is not recommended as a production path and the buyer's engineering team should keep the original drive in service while a same-brand current-generation candidate is located.

How the desk handles the inquiry

When a buyer comes in with a discontinued servo drive and an existing motor, the workflow we follow is:

1. Read the motor nameplate and the motor's datasheet, or read a clear photo of the motor's nameplate. We need frame size, rated power, rated speed, encoder protocol, encoder resolution, brake presence, and connector family.
2. Identify whether the original drive's manufacturer still produces a current-generation equivalent (within the same brand). If yes, that is the lowest-friction path and we quote it first.
3. If no current-generation equivalent exists inside the original brand, look at adjacent brands that publish the same encoder protocol and current rating family.
4. Build a written comparison on the four axes above.
5. Send the comparison to the buyer with a one-line verdict per axis and the datasheet sources.
6. The buyer decides whether to commission the substitution. The integrator owns the parameter migration and the commissioning.

We do not commission the drive on the bench in our facility, and we do not write the parameter set. We are a sourcing desk, not a system integrator. The desk's job is to keep the four axes honest on paper; the integrator's job is to honour them on the bench.

What the quote lists on every line

A quote on a servo drive substitution lists four things per line:

• Pricing: indicative and depends on the specific drive and condition. Servo drives are quoted at the part-number level; we do not bundle across line items.
• MOQ: typically one piece on discontinued drives, but a drive on the current production line may carry a pack quantity. The MOQ is stated on the line, not assumed.
• Lead time: quoted per order, not held over from a previous quote. A drive that was on the shelf yesterday can be gone tomorrow; lead times are not transferable.
• Condition: every line carries a condition code — new surplus, refurbished, or used. A drive that came out of a decommissioned machine with no bench record is used, not refurbished, and the line is labelled as such.

We do not promise a fixed delivery window. Dispatch under DDP into Russia, Kazakhstan, or Belarus is arranged where the quotation states it; we screen end users and end uses, classify before quoting, and decline transactions that cannot be screened. The condition on every line is the buyer's protection against a refurbished drive being relabelled as a new one.

What goes on a buyer's first message

The first message does not need to be a finished engineering dossier. A photo of the motor nameplate, a photo of the drive's marking, the application (vertical axis, horizontal axis, indexing conveyor), and the fault or downtime description are enough to start. If the buyer has the original drive's datasheet, attach it. If the buyer does not, the marking on the drive itself plus the machine's model is often enough to look up the drive's datasheet on the manufacturer's public archive.

If the inquiry is too thin to identify the motor's encoder protocol and brake wiring, we come back with two or three clarifying questions rather than quoting a drive on assumptions. The clearance is faster than a wrong quote, and a wrong quote on a closed-loop pairing costs the buyer a commissioning day.

The takeaway

A servo drive is replaceable. A servo pairing is not. When the original drive is discontinued, the work is on the motor side: confirm the encoder protocol, confirm the winding current rating, confirm the brake wiring, and confirm the cable connector pinout. Once those four points are matched (or admitted as differs), the drive substitution can proceed. The cross-reference report that comes out of the desk is the four-axis table, the unknown-axis admission, and a clear refusal of any drop-in assertion.

For a sourcing inquiry on a discontinued servo drive with the existing motor still on the shaft, send your nameplate photo and the original drive's marking through the inquiry page. The cross-reference report is the next step; the integration step is the buyer's. To request a quote on a single servo line, send us your BOM via the procurement page; for a multi-axis cross-reference table, the compare page produces the side-by-side. Independent distributor note: we are a sourcing desk, not a system integrator, and we do not commission the drive on your motor in your facility.

Data Notes

By aoctrl sourcing desk. Last updated: September 2026. Independent industrial automation distributor and China-based sourcing desk. Not an authorized distributor of any brand on the catalogue; not a system integrator; not a repair house. Per-line condition (new surplus / refurbished / used) is stated on every quote; pricing is indicative and confirmed per line on the quotation; lead times are quoted per order. Where the quotation states DDP into Russia, Kazakhstan, or Belarus, dispatch is arranged under that term; we screen end users and end uses, classify before quoting, and decline transactions that cannot be screened. Verify any servo drive pairing against the original manufacturer datasheet and your own qualification process before commissioning on the existing motor.

FAQ

What information do you need from a discontinued servo drive inquiry?

The motor nameplate photo (frame size, rated power, rated speed, encoder protocol, encoder resolution, brake presence, connector family), the original drive's marking or model number, the application axis (vertical, horizontal, indexing), and a brief description of the fault or downtime. Without the encoder protocol and brake wiring on the motor, we cannot build the four-axis comparison.

Can a third-party drive run a Yaskawa, Mitsubishi, Inovance, or Delta motor?

Sometimes. The encoder protocol and connector pinout are the deciding factors. A drive from another brand will not read the motor's encoder without a transition module or motor rewire, and the report names the axis that blocks the substitution. Same-brand drive substitution on a next-generation servo drive (for example, an Inovance IS620 on the same encoder protocol as an Inovance ISMV motor) is the lower-friction path.

Do you quote on a label match, or only on a verified pairing?

Only on a verified pairing. A label match is necessary but not sufficient. The report lists the axes that match and the axes that differ, and the buyer's engineering team decides whether to commission the substitution.

Do you bench-test a servo drive before shipping?

For new-surplus and refurbished units we publish what the desk can verify: the marking, the condition code, and the visible connector integrity. We do not run a closed-loop bench-test on a servo drive in our facility; that work belongs to the buyer's commissioning engineer on the buyer's motor. The pre-dispatch photo record shows the unit's marking, label, and connector condition.

Will you commission the drive on the motor in our facility?

No. We are a sourcing desk, not a system integrator. The buyer's electrical integrator owns the parameter migration, the wiring, and the commissioning of the substitute drive on the existing motor.

Is the replacement drive cross-referenced or current-production?

Both are quoted on the same line. If the original brand still publishes a current-generation drive that supports the motor's encoder protocol, that is the lowest-friction option. If not, we list adjacent-brand candidates and let the buyer's engineering team pick.

How is the servo drive shipped under DDP, and who handles customs clearance into Russia?

Where the quotation states DDP, we arrange dispatch to the named destination; the buyer is responsible for the import side. We screen end users and end uses, classify before quoting, and decline transactions that cannot be screened. The dispatch and the customs brokerage under DDP are quoted per order; transit times are not transferable from a previous quote.