Loading Motoman MRC Parameters: Resolving Alarms 200 and 120 on Used MRC K10 Robots

Bringing two used Motoman MRC K10 robots back into service requires more than just applying power. When the robots arrive from an auction or decommissioned line, several subsystems have typically been disturbed: S-axis (base rotation) wiring may be detached, absolute encoder backup batteries may be dead, and the on-board parameter file may have been erased or may not match the mechanical configuration that the controller is now detecting. The first two alarms the commissioning engineer is likely to face are Alarm 200 (data discrepancy / parameter initialization required) and Alarm 120 (S-axis servo error). This article walks through root cause analysis, parameter loading, encoder battery replacement, and verification for a typical MRC / XRC commissioning sequence.

1. MRC Controller Family Overview

The Motoman MRC (Motion Robot Controller) is the predecessor to the XRC, DX200, and YRC1000 controller generations. It was paired with several six-axis articulated robots, including the K10 (10 kg payload), SK10 (a shelf-mounted variant), UP50, and the dual-arm seat-rail handling configuration that Johnson Controls used for Toyota seat rail welding. The controller's three servo packs (typically labeled SV#1, SV#2, and sometimes SV#3) drive the S, L, U, R, B, and T axes.

Servo assignment on a standard K10 / UP50 with MRC is roughly:

If the original application used external positioners or turn-tables, additional axes can be assigned to SV#3 or to a coordinated servo block. Mirrored / ganged robots used on the same fixture line will often have their S-axis wiring parked at the S/U connector block on the base of the arm, terminated with mating female plugs that loop through the turn-table interface.

2. Alarm 200 — Data Discrepancy / Parameter Mismatch

Alarm 200 on the MRC/XRC indicates that the absolute position counter stored in the encoder backup memory does not match the parameter file loaded in the controller. After a dead battery, encoder replacement, or first-time power-up of a long-stored robot, the position counters in the encoders (Epson / Tamagawa absolute multiturn) read as out-of-range relative to AxPMAX / AxPMIN pulse limits in the parameter set.

The fault path is:

1. Controller requests absolute position from each axis encoder.
2. Encoder returns raw pulse count (multiturn = 0 on first read after power-up).
3. Controller compares pulse count to the parameter file's AxPMAX / AxPMIN window.
4. If the count is outside the window (or the parameter file is missing / wrong revision), Alarm 200 raises and all servos remain OFF.

Root cause for an auction robot is almost always one of:

• Absolute encoder backup battery is dead (or was removed with the encoder for shipping).
• The parameter file was not preserved and the controller was re-initialized to factory defaults.
• The S/L/U/R/B/T motor or encoder connectors were separated from the controller during tear-out, and the controller has lost the calibration of that axis.

3. Alarm 120 — S-Axis Servo Error

Alarm 120 indicates a servo error specifically on the S-axis, typically:

• Overcurrent / overtravel detected on SV#1 channel 1.
• Encoder feedback loss (open wire, bad connector, dead encoder).
• Position error exceeding tolerance for the configured acceleration / payload.

When the on-screen message shows "NSN UXU 120" with the S character highlighted, the controller is indicating that the S-axis (and possibly U- and X-related lines) is the source. The "NSN UXU" string is a non-specific servo position-error prefix and the highlighted letter points at the offending axis. SV#1 and SV#2 numbers listed in the alarm detail tell the engineer which physical servo pack channel is reporting.

On a robot that was ganged to a turn-table, an open female S / S- / CR wire pair at the S/U connector block is the most common cause. The pair was originally looped through the turn-table wiring harness; if the harness was cut at tear-out, the encoder feedback return path is broken.

4. Pre-Commissioning Safety and Preparation

Before any parameter load, power cycle, or servo test:

1. Lock out and tag out the main 480 V three-phase feeder. Verify zero energy with a properly rated meter at the disconnect.
2. Confirm the controller's 24 VDC control power is OFF when mating or unmating encoder cables.
3. Inspect the manipulator for mechanical shipping damage: S-axis rotation, L-arm, U-arm, R/B/T wrist assembly, and the absolute encoder covers on each motor.
4. Replace the absolute encoder backup batteries in all six axes before the first absolute-position reset. Battery part number for the K10/SK10/UP50 generation is typically Yaskawa HW9470932-A or HW0383966-A (3.6 V lithium, AA-size, with a 200 mm lead and JST connector). Confirm the part number against the controller BOM before ordering.
5. Have a clean copy of the Yaskawa Motoman Maintenance Manual for the specific K10 robot and MRC controller on hand. The Yaskawa documentation portal is the authoritative source.

5. Locating or Recovering a Valid Parameter File

Three parameter file sources are possible, ranked by preference:

Per Yaskawa Motoman field practice, end users are permitted to load the SC (system configuration), AP (application), and RS (robot-specific) parameter groups. The RS parameters must be matched exactly to the mechanical configuration of the connected robot: payload, arm length, gear ratio, and absolute pulse range. A parameter set from a different K10 (not SK10) will load the correct RS group because the K10 base robot is identical regardless of payload tooling, but application constants such as user frames, tool frames, and home position pulse counts will need to be re-taught.

If the auction did not include the original CMO floppy disk or PCMCIA card, the options are:

1. Call Yaskawa Motoman Service and request the parameter file by controller serial number. They typically keep records for the life of the controller and can supply a backup on a fresh CMO card for a modest fee plus registration of the controller in your company name.
2. Run the controller's Automatic Calibration routine to re-derive the absolute position of each axis. The robot is driven to the home-pulse position and the encoder counter is re-zeroed. This requires the robot to be free of mechanical obstructions and to have a fresh backup battery installed.
3. Use a third-party tool (e.g. RoboDK) to import an ALL.PRM file and inspect the pulses-per-degree constants to confirm the file matches the robot. RoboDK's Motoman robot documentation describes the drop-in workflow for the ALL.PRM file.

6. Serial Cable for Parameter Upload / Download

The MRC controller uses an RS-232C serial port (DB-9 female on the controller, labeled "RS-232C" or "COMM") to communicate with a PC running Motoman's DOS-based PC Editor or the MotoCom32 Windows tool. The cable pin-out is:

Settings: 9600 / 19200 baud (try 9600 first), 8 data bits, no parity, 1 stop bit, hardware flow control. On the controller side, set the I/O port to RS-232C in the system configuration menu and set the protocol to TRANSMIT for upload or RECEIVE for download.

7. Loading the Parameter File — Step by Step

The following procedure assumes a PC with Motoman PC Editor (or equivalent) and a verified ALL.PRM file on hand.

1. Connect the serial cable to the controller and to the PC. Power up the PC first, then the controller.
2. On the MRC, navigate to SETUP → SYSTEM → PARAMETER → I/O and configure the serial port (9600 8N1, hardware handshake).
3. On the PC, launch PC Editor and select Communications → Online. Confirm the controller replies with the system banner (firmware version, controller serial number, robot model).
4. From the PC, select File → Transmit → Parameter File and choose the ALL.PRM file. The transmission takes 30–60 seconds for a full K10 parameter set.
5. The controller will display RECEIVING and a percentage progress. Wait for the controller to display RECEIVE COMPLETE.
6. Cycle controller power (full 480 V OFF, 24 VDC OFF, then reapply). The controller will re-initialize with the new parameter file.
7. Re-enter SETUP → SYSTEM → SECURITY and confirm the robot model displayed matches the mechanical nameplate (K10, not SK10, not UP50).

8. Absolute Position Reset for the S-Axis

After the parameter file is loaded and Alarm 200 has cleared, the S-axis (and any other axis that raised a 120) needs the absolute position re-initialized. Procedure:

1. From the teach pendant, navigate to SETUP → ROBOT → ABSOLUTE RESET.
2. Select the S axis.
3. Press ENABLE and hold the deadman switch in the middle position. Press MODIFY.
4. With the controller in TEACH mode, manually rotate the S axis to the home-pulse mechanical mark. The mechanical home mark is a scribe line on the S-axis housing that aligns with a corresponding line on the base. A standard K10 home position has the arm centered over the base with a tolerance of ±0.5°.
5. Press EXECUTE. The controller writes the new absolute position to the encoder backup memory and clears the absolute error flag.
6. Repeat for the L, U, R, B, T axes in sequence.

9. Inspection of the S/U Connector Block and Turn-Table Harness

For auction robots that were originally ganged to a turn-table, the S/U connector block at the base typically has a captive harness routed to the positioner. The harness carries:

• S motor power (3-phase, 200 V class)
• S encoder feedback (5 V differential, 6 or 8 wire)
• CR (cable reel) auxiliary power
• Brake release lines

If the turn-table was removed at tear-out, the original installer may have left a loop-back jumper consisting of female-to-female S, S-, and CR plugs that re-closed the circuit. A loose or missing jumper produces exactly the Alarm 120 / SV#1 fault pattern. Verify:

1. Continuity between the S motor power pins and the matching pins on the controller's SV#1 connector at the cabinet.
2. Continuity between the encoder A/A-, B/B-, Z/Z-, +5V, and GND lines through the S/U block and out to the S-axis motor encoder.
3. Brake release voltage (24 VDC nominal) is present on the brake terminals when the deadman switch is held in TEACH mode and the controller is in servo-ready state.

10. Encoder Backup Battery Replacement

Each axis motor has a small PCB on the back of the absolute encoder that holds a 3.6 V lithium backup cell. On the K10 / SK10 / UP50 generation, the cell is a solder-tab AA-size lithium thionyl chloride (Li-SOCl2) cell. Replacement procedure:

1. Power down the controller and wait at least 60 seconds for the bus capacitors to discharge.
2. Remove the encoder cover on the back of the motor (typically 4 small Phillips screws).
3. Desolder the old cell. Note the polarity — the positive tab is the inner one on most encoder boards, but always verify against the silk-screen mark.
4. Solder in a fresh cell of the same chemistry and capacity (e.g. Tadiran TL-5104 or Xeno XL-060F). Do not use alkaline or Li-ion cells — their discharge curve will not match the encoder's brown-out detection and will trigger false absolute position errors.
5. Reassemble the encoder cover. Confirm the gasket is intact to prevent contamination.
6. Repeat for each of the six axes. Always replace all batteries as a set — mixing old and new batteries on a robot will lead to a partial failure within months.

11. Verification Procedure

After the parameter load, absolute reset, and battery replacement, run the following verification sequence:

1. Power up the controller. Confirm no Alarm 200 on the diagnostic screen.
2. Enable servos from the teach pendant. Confirm no Alarm 120 and all six axes show READY.
3. In TEACH mode, jog each axis through its full range of motion at 10% speed. Confirm no overtravel, no position error, and no abnormal noise.
4. Run the controller's BUILT-IN DIAGNOSTIC routine (path: SETUP → DIAGNOSTIC → ALL AXES). Each axis will perform a self-test motion of a few degrees in each direction.
5. Create a simple test program: MOVJ P001 VJ=20.00 to the home position, then MOVJ P002 VJ=10.00 to a small offset, then MOVJ P001 VJ=20.00 return. Run the program in TEST CYCLE three times.
6. Confirm the robot returns to the home pulse position within ±2 pulses on each axis.
7. Power down, wait 30 seconds, power up, re-enable servos. Repeat the home return. If the absolute position is preserved (no Alarm 200), the battery replacement was successful.

12. Troubleshooting Matrix

13. Registering the Robot with Yaskawa Motoman

Auction robots are typically not in the buyer's name in Yaskawa's system, and access to the original backup parameter files is often gated on registration. Open a service ticket with Yaskawa Motoman North America (or your regional service desk), provide:

• Controller serial number (printed on the CPU board nameplate inside the cabinet)
• Robot serial number (printed on the base of the manipulator)
• Application the robot was originally sold for (if known)
• Proof of ownership (bill of sale, auction invoice)

Yaskawa will then register the assets in the buyer's name and provide a parameter backup, application notes, and a recommended spare parts list. The fee is modest and is the single most cost-effective step in commissioning an auction robot.

14. Common Pitfalls on Auction Robots

• Mixing K10 and SK10 parameter sets. The K10 and SK10 are mechanically similar but the SK10 has a different base mounting and S-axis moment arm. A SK10 parameter set on a K10 will produce constant position errors near the S-axis limits.
• Re-using old brake release contactors. Brake contactors that have been sitting in storage for years often have oxidized contacts and will fail under load. Replace as a set with the parameter load.
• Skipping the absolute reset sequence. Loading the parameter file does not clear the absolute position counters in the encoders — the controller must go through the absolute reset sequence for each axis.
• Ignoring the controller's calendar battery. The MRC has an internal calendar/clock battery separate from the encoder batteries. A dead calendar battery can corrupt the parameter file checksum on power-up.

15. Long-Term Reliability Recommendations

After successful commissioning:

1. Schedule encoder backup battery replacement every 5 years regardless of alarm history.
2. Maintain an off-controller backup of the parameter file on a USB stick or a network share. Export the parameter file via the serial port after every successful commissioning event.
3. Keep the controller cabinet clean. Dust on the CPU board or the absolute encoder covers is a common cause of intermittent absolute position errors.
4. Run the built-in diagnostic routine monthly to confirm all six axes are still returning to home within tolerance.