SRVO-068

Power down and verify alarm axis

Note the axis number from the alarm (displayed as 'Group:X Axis:Y'). Power down the controller completely. Wait 60 seconds for capacitor discharge before opening any cabinet doors.

High voltage remains in servo amplifiers for up to 5 minutes after power-down. Verify voltage with meter before touching connections.

Inspect pulse coder connector at servo amplifier

Locate the servo amplifier for the faulted axis (marked J1-J6 or E1-E8). Find the encoder connector (typically labeled 'PC' or 'ENC' - a smaller multi-pin connector separate from power). Check for loose connector, bent pins, corrosion, or contamination. Disconnect and reconnect firmly - you should hear/feel a positive lock.

On R-30iB Plus controllers, the encoder connectors use locking tabs. Press the tab fully before pulling - forcing it can break the connector body.

Inspect pulse coder connector at robot base

Remove the robot base cover to access the cable entry point. Locate the pulse coder cable connector (separate from motor power cables, usually a smaller rectangular connector). Check connector seating, inspect pins for damage, and look for coolant or oil contamination that could cause intermittent connection.

The base connector typically has a colored band or label matching the axis number. Document connector positions before disconnecting anything for proper reassembly.

Perform visual continuity check

With power still off, use a digital multimeter in continuity mode to check pin-to-pin continuity from the amplifier connector to the robot base connector. Consult the Connection Diagram in the Maintenance Manual (MAROCON00E document) for your specific robot model to identify correct pin assignments for the serial pulse coder signals (typically CLK, DATA, and ground).

Flex the cables near connectors while testing - intermittent continuity indicates internal wire breaks that won't show in static tests.

Test with power restored

Reconnect all cables, restore power, and attempt to clear the alarm. Navigate to MENU > ALARM > F5[RESET] or hold SHIFT and press RESET on teach pendant. If alarm immediately returns before motion, the cable connections are likely good and the fault is in the encoder or amplifier.

Do not attempt to jog the axis if alarm persists - this can cause position loss requiring re-mastering.

Check cable flex history and visual condition

Review robot operating hours (MENU > NEXT > STATUS > [F1] CSTRHIS). Cables typically fail between 20,000-40,000 hours depending on application. Inspect the cable dress from base to tool - look for excessive wear marks, kinking, cable ties cutting into bundles, or areas where cables rub against the robot structure.

Check the J3 arm area especially on M-series robots - this is the highest flex point and most common cable failure location.

Perform resistance measurement test

Power down completely. At the servo amplifier end, disconnect the pulse coder connector for the faulted axis. Using a precision ohmmeter, measure resistance of each encoder signal wire to ground and to adjacent wires. Serial encoders typically show 100-120 ohms termination resistance. Compare readings to a known-good axis. Variance >10 ohms suggests cable damage.

Document all measurements. Gradual resistance increase over time (check maintenance records) indicates progressive wire strand breakage before complete failure.

Check cable shield ground continuity

Verify the pulse coder cable shield has continuity to the controller ground bar. Open the controller cabinet and locate the ground terminal block (typically on right side panel). The cable shields should be terminated to this bar with ring terminals. Measure resistance from shield to ground - should be <1 ohm. Poor grounding allows EMI to corrupt encoder signals.

Do not rely on paint or anodized surfaces for ground. Shield terminations must contact bare metal.

Perform flex test on suspected cable sections

With power off and encoder connector separated, manually move the affected joint through its full range of motion slowly while monitoring cable continuity with a meter. Have a second person watch the meter while you manipulate the joint. Intermittent open circuits during movement confirm internal cable damage requiring replacement.

Test at both extremes of joint rotation and at mid-stroke where cables experience different flex stress patterns.

Review error logs for intermittent history

Check if this alarm occurred previously: MENU > ALARM > F2[ALARM LOG]. Look for pattern of SRVO-068 on same axis, or related alarms like SRVO-075 (pulse coder comm error). Multiple occurrences over weeks/months indicate progressive cable failure rather than sudden connector issue.

Press F3[DETAIL] on any logged alarm to see exact date/time stamp and any secondary alarms that occurred simultaneously.

Verify cable integrity before encoder replacement

Before condemning the encoder, confirm cable testing from previous cause blocks shows good continuity, proper shielding, and solid connections. Replacing an encoder without verifying cable condition is the most common misdiagnosis and wastes costly parts and labor.

If possible, swap the pulse coder cable with an identical axis (e.g., swap J2 and J3 cables). If the alarm moves to the other axis, the cable is faulty, not the encoder.