Resolving Yasnac MRC Alarm 200: Robot Conform Parameter Error

The Yasnac MRC (Machine Robot Controller) is a legacy Motoman architecture that predates the DX200 and FS100 platforms now shipping under the Yaskawa Motoman brand. When Alarm 200 raises on the teach pendant or operator panel, the controller is reporting that one or more robot conform parameters—the mechanical/kinematic data that bind the software to the specific arm in the cell—have failed a checksum, range, or consistency check. In nearly every case, servo power remains inhibited until the conform set is restored to a valid image. This article documents the alarm definition, the dual-battery architecture that backs those parameters, the reload procedure from a 3.5" floppy backup, and the verification steps required to bring the manipulator back on line without bricking the controller.

1. Problem Definition: Alarm 200 Behavior

Alarm 200 belongs to the Group 2 alarm class on the MRC, which covers system and parameter integrity faults. On the pendant, the message reads as either:

• AL.200 ROBOT CONFORM PARAMETER
• AL.200 ROBOT CONFORM DATA ERROR
• AL.200 ROBOT PARAM. ERROR (xxxx) where (xxxx) is a sub-code identifying the offending conform record block

Observable symptoms in the field:

Because the conform set defines the manipulator's mechanical envelope, payload constants, and axis mapping, the controller refuses to energize the servo stacks until valid data is restored. This is a hard interlock; clearing the alarm from the pendant (RESET key) will not enable servo power when Alarm 200 is active.

2. Root Cause Analysis: Why the Conform Set Fails

The conform set lives in battery-backed CMOS SRAM on the MRC's main CPU board. Several failure modes produce Alarm 200:

1. System battery depletion or interruption. The MRC uses two separate lithium battery packs. The system battery maintains the CMOS/RAM that holds parameters, I/O configuration, and the operating mode. A momentary disconnect during a service event, or a battery that has dropped below its working threshold, is the most common cause.
2. Encoder battery depletion. A separate battery backs the absolute encoders on each axis. While encoder backup loss typically produces a different alarm (e.g., AL.410 / AL.420 range on Motoman controllers of this era), a fully discharged encoder battery can also disturb the boot-time conform consistency check if the controller cannot confirm position reference for the first axis.
3. Checksum / parity corruption. A noise event on the backplane, an aborted write, or a write attempt by an unauthorized parameter change can leave the conform record with a bad checksum. The MRC validates the conform set at boot and at every servo-on request.
4. Incomplete or truncated reload. Attempting to load a parameter file written for a different robot model, or interrupting a floppy load mid-write, leaves the conform set in a hybrid state. The boot routine detects the inconsistency and raises Alarm 200.
5. Hardware fault on the CPU board. Failed CMOS RAM or a degraded supercapacitor on the main board. Less common, but it produces identical symptoms and survives battery replacement.

3. Battery System Architecture

The MRC maintains two independent battery circuits. Identifying which circuit has failed is the first diagnostic step.

Additional encoder backup batteries may be installed in the base of the manipulator itself on some installations. If the cell in the base has failed, the controller may boot with encoder position data cleared, producing a different alarm class. However, the absence of valid encoder data can also cause conform validation to fail because the controller cross-references position with the conform envelope at boot.

4. Pre-Reload Verification Checklist

Before committing to a parameter reload, walk through the following checks. Reloading a wrong-version backup is the fastest way to escalate a 30-minute job into a multi-day recovery.

1. Confirm battery state. With the controller powered, measure both battery voltages at the test points or battery leads. Replace any cell at or below 3.3 V under load. If you replace a system battery, do it hot (with the controller live) to preserve residual data.
2. Confirm the floppy drive. The MRC uses a 3.5" floppy drive. Heads may be dirty; media may be degraded. Try a known-good, freshly formatted 1.44 MB DOS disk.
3. Verify the backup file matches the robot. The parameter file header should identify the robot model (e.g., SK6, UP20, EA1400N) and the controller serial number. If the backup is from a different manipulator on the same controller, the conform block will write valid data for a different mechanical envelope—the controller will then either reject the load or, worse, allow it and produce motion errors at the first jog.
4. Record current sub-codes. If the pendant displays a sub-code in parentheses after Alarm 200, transcribe it. The sub-code identifies the conform block at fault and helps confirm whether the corruption is in the robot arm constants, the payload table, or the user-modified parameters.
5. Capture the current parameter page. Use the pendant's MENU → PARAM path to dump the current A group (and B/C groups if accessible) to the printer port or to a fresh floppy. This gives you a fallback if the reload produces unexpected results.

5. Parameter Reload Procedure from Floppy Backup

The MRC parameter load uses the pendant's external memory functions. The exact path varies slightly by pendant firmware revision, but the sequence below is canonical for the majority of fielded units.

1. Place the controller in TEACH mode.
2. Insert the parameter backup floppy into the drive.
3. From the main menu, navigate to EX.MEM → LOAD → PARAM (External Memory → Load → Parameter).
4. Select the parameter file corresponding to the robot. The display will show the file name and creation date; verify the model number on the second line.
5. Confirm the security prompt. The MRC requires the four-digit parameter security code before it will overwrite the conform set. Without the correct code, the load is rejected silently and Alarm 200 remains.
6. Execute the load. The display will show progress as each parameter group (A0–A99, etc.) is written. Do not power off or remove the disk during the write.
7. When the load completes, the controller may auto-cycle. Allow the full boot to complete; do not interrupt.
8. After reboot, return to MENU → ALARM and verify Alarm 200 is cleared. Other alarms (e.g., encoder absolute position lost) may remain if the encoder battery was depleted; address those separately.

6. Full Re-initialization (Cold Start)

If a valid backup does not exist, or if the reload fails to clear Alarm 200, a full re-initialization is the next step. This operation clears all parameters—including the conform set—and requires a reload afterward.

1. Back up the current B and C group parameters (user-modifiable, non-conform) before initialization. Initialization wipes these as well.
2. Enter MENU → SETUP → INITIALIZE.
3. Enter the security code when prompted.
4. Select ALL CLEAR (full parameter reset) rather than a partial reset. A partial reset will leave the conform set in an undefined state.
5. Confirm the prompt. The controller will reboot with factory-default parameters and no conform data.
6. Load the robot's conform set from the backup floppy. Without this, the controller cannot identify the arm and will not enable servo power.
7. Load the application-specific B/C group parameters.

7. Servo Power Enable Verification

After the parameter load, walk through the enable sequence deliberately. The MRC has multiple interlocks that must all be satisfied before the servo stacks close.

Once the SERVO ON lamp is on, perform a low-speed jog of each axis in TEACH mode to confirm the conform set matches the mechanical envelope. Pay particular attention to:

• Axis 1 (base rotation) — verify the displayed joint angle matches the physical pose within ±0.5°.
• Axis 2 (shoulder) and Axis 3 (elbow) — verify the arm does not strike the worktable at expected positions. A wrong payload constant or wrong arm-length value in the conform set can produce motion that is geometrically valid for the controller but invalid for the cell.
• Axis 4, 5, 6 (wrist) — verify orientation matches the expected roll/pitch/yaw.

8. Related Alarm Codes on the MRC

Alarm 200 rarely appears in isolation on a long-out-of-service controller. Expect to encounter:

9. Preventive Maintenance for Legacy MRC Cells

Because the MRC is past end-of-life, prevention is the most cost-effective intervention. Schedule the following checks at every preventive maintenance visit:

• Battery voltage check — annually under load, with the controller live.
• Backup verification — every 6 months, perform a full parameter save to a freshly formatted floppy and store a copy off-site. Verify the file size is consistent with a full parameter set; a truncated file is a sign of media degradation.
• Drive maintenance — clean the floppy drive heads annually with a 3.5" cleaning disk. Drives of this era are mechanical and fail predictably.
• Security code record — store the parameter security code in a controlled document. A missing code on a dead controller is a critical incident.
• Spare battery stock — keep a minimum of two matched battery packs in stock. Lead time on a confirmed-correct cell is often longer than the cell's installed life.

10. Legacy Support and Documentation

Yaskawa Motoman maintains a self-service documentation portal where manuals for legacy controllers—including the MRC—can be requested or downloaded. The portal is the authoritative source for controller-specific alarm lists, parameter tables, and maintenance procedures:

Motoman Robot & Controller Manuals (motoman.com product documentation portal)

For controllers no longer covered by the portal, third-party specialists with Motoman MRC experience can supply copies of the original Operator's Manual, Maintenance Manual, and Parameter List. Engagement with a specialist is recommended for any reload where the backup file's model number cannot be confirmed, or where the security code is unknown.

11. Field-Proven Diagnostics Summary

12. Safety and Operational Constraints

Work on an MRC must follow standard industrial robot safety practice. Even when the controller is in a fault state, the manipulator's brakes hold the axes in position. Releasing brakes manually without servo power requires a separate brake-release procedure that bypasses normal interlocks — this is an exceptional maintenance step, not a recovery step for Alarm 200.

• Lock out and tag out the main disconnect before opening the cabinet.
• With main power on for battery measurement, observe arc-flash and exposed bus cautions at the cabinet door.
• Do not bypass the parameter security code by clearing CMOS. This will erase the I/O configuration and require a full re-initialization.
• Do not load a parameter file from a robot with a different payload rating or reach class. The conform set encodes the mechanical envelope; a mismatched load is a collision hazard at the first motion.

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