TOSHIBA TN721 Series Modules

Technical Dossier

Product Details And Specifications

TOSHIBA TN721 / GTN721 Series: Comprehensive Module Range and Technical Overview

The TOSHIBA TN721 and GTN721 series are servo control motor power supply modules deployed extensively across global heavy industry sectors, including petrochemical refineries, nuclear power auxiliary systems, steel rolling mills, and large-scale process automation plants. Manufactured by Toshiba Corporation's Industrial Systems division in Japan, these units serve as the regulated DC power backbone for TOSHIBA's servo drive ecosystems. Their robust design tolerates high-vibration environments and wide ambient temperature ranges, making them a preferred choice for continuous-duty installations where unplanned downtime carries significant operational cost.

The TN721/GTN721 platform occupies a critical position in TOSHIBA's legacy servo infrastructure. Installed base counts in Asia-Pacific and EMEA regions remain substantial, with many facilities operating these modules well beyond their original design lifecycle. DriveKNMS maintains dedicated stock and sourcing channels for this series to support long-term plant maintenance programs.

The Evolution of TN721 / GTN721 Architecture

The TN721 series was introduced as part of TOSHIBA's second-generation servo drive platform, succeeding earlier thyristor-based power conversion units. The architecture centers on a regulated switch-mode power supply topology that provides isolated DC rails to the servo amplifier control board, encoder interface circuitry, and regenerative braking resistor networks.

Early TN721 variants used through-hole PCB construction with discrete IGBT pre-driver stages. Subsequent GTN721 revisions transitioned to surface-mount technology on the control sub-board while retaining the original power stage form factor, ensuring backward mechanical compatibility with existing cabinet installations. This design continuity allowed facilities to upgrade control electronics without full cabinet replacement — a significant factor in the series' longevity.

Compatibility considerations: TN721 and GTN721 modules interface with TOSHIBA servo amplifier families including the VF-S9, VF-AS1, and TOSVERT series. Backplane connector pinouts are standardized across the TN721 generation, but firmware revision levels must be matched to the host drive controller to avoid parameter initialization errors. Facilities migrating from TN721 to GTN721 should verify DC bus voltage tolerance specifications, as GTN721 units introduced a wider input voltage window (±15% vs. ±10% on original TN721).

The series is now classified as mature/end-of-production by TOSHIBA. No direct OEM replacement has been announced for the TN721 form factor; the recommended migration path is to TOSHIBA's current TOSVERT VF-MB1 platform, which requires mechanical and wiring adaptation. For facilities unable to undertake full drive replacement, long-term spare parts support through authorized distributors and specialist suppliers remains the primary maintenance strategy.

TN721 / GTN721 Full Catalog & Functionalities (SKU List)

The following SKUs represent the documented TN721/GTN721 series range. Each entry reflects a distinct functional variant within the servo power supply and associated module ecosystem:

TN721: Base servo control motor power supply module; standard DC output rating for TOSHIBA servo amplifier series.
GTN721: Enhanced-revision power supply with extended input voltage tolerance and improved EMC filtering.
TN721A: Variant A — modified output capacitor bank for high-cycle duty applications.
TN721B: Variant B — reinforced inrush current limiting circuit for cold-start environments.
TN721C: Variant C — conformal-coated PCB for high-humidity industrial environments.
GTN721A: GTN721 with variant A output stage; compatible with VF-AS1 amplifier series.
GTN721B: GTN721 with extended temperature rating (-10°C to +55°C operating).
GTN721C: GTN721 with integrated soft-start relay for reduced DC bus surge on power-up.
TN721-1: Single-axis power supply configuration; reduced output current rating.
TN721-2: Dual-axis power supply configuration; parallel output bus architecture.
TN721-3: Three-phase input variant; for 380–480 VAC three-phase supply environments.
GTN721-1: GTN721 single-axis variant with updated gate driver IC revision.
GTN721-2: GTN721 dual-axis variant; increased bulk capacitance for regenerative load handling.
GTN721-3: GTN721 three-phase input variant; CE-marked for European installation compliance.
TN721-R: Regenerative braking interface module; pairs with TN721 base unit for dynamic braking duty.
GTN721-R: GTN721-compatible regenerative module with upgraded IGBT switching frequency.
TN721-F: Field-retrofit kit variant; includes updated firmware EEPROM and terminal adapter plate.

Sourcing Hard-to-Find & Obsolete TN721 / GTN721 Parts

TOSHIBA has ceased volume production of the TN721 and GTN721 series. OEM lead times for any remaining new-old-stock (NOS) units through standard distribution channels are indeterminate. DriveKNMS operates a dedicated procurement desk for end-of-life TOSHIBA servo components, with the following sourcing capabilities for the TN721/GTN721 range:

— Verified NOS units sourced from decommissioned plant inventories across Japan, South Korea, and Germany.
— Professionally refurbished units with full capacitor replacement, IGBT inspection, and DC output re-calibration.
— Component-level repair service for boards with failed gate drivers, blown fuse elements, or degraded electrolytic capacitors.
— Cross-reference matching for facilities holding partial part numbers or legacy TOSHIBA internal codes.
— Emergency same-day dispatch for in-stock units to minimize unplanned downtime impact.

All sourced TN721/GTN721 units are documented with traceability records including origin facility, inspection date, and test report reference number. DriveKNMS does not supply untested or uninspected units for safety-critical servo applications.

Quality Control for the TN721 / GTN721 Range

The TN721 and GTN721 power supply modules present specific test challenges due to their integrated backplane interface and multi-rail DC output architecture. DriveKNMS applies the following test protocol to all units processed through its facility:

Visual Inspection: Full PCB inspection under 10× magnification for cracked solder joints, swollen capacitors, burnt resistor networks, and corrosion on connector pins.
Capacitor ESR Measurement: All bulk electrolytic capacitors tested for equivalent series resistance against manufacturer datasheet limits. Units with ESR exceeding 150% of nominal are recapped prior to dispatch.
DC Output Load Test: Each output rail loaded to 80% of rated current for 30 minutes. Output voltage stability, ripple voltage (measured at 20 MHz bandwidth), and thermal performance are recorded.
Backplane Connector Test: Connector pin continuity and insulation resistance verified using a 500 VDC megohmmeter. Minimum acceptable insulation resistance: 100 MΩ.
Functional Integration Test: Where test fixtures are available, units are powered within a TOSHIBA servo amplifier test rig to verify correct initialization, fault relay operation, and communication with the host controller.
Final Documentation: Each unit ships with a test report stating pass/fail criteria, measured values, and inspector ID.

For TN721, GTN721, and related TOSHIBA servo module inquiries: