Diagnosing a Robot That Will Not Calibrate

Confirm which mastering method is failing

Identify whether fixture position, zero position, quick, or single-axis mastering is being attempted, since each reads position differently and fails at a different point. The Master/Cal screen lists all of them as options 1 through 7, ending with CALIBRATE. Knowing the intended method tells you which reference (a jig, the zero-degree witness marks, or stored quick-master reference points) actually has to be correct.

Read the alarm history before touching anything

Open the alarm log on the pendant and record every active and recent fault, because the calibration refusal is usually a downstream symptom. A robot that reports it is not mastered (SRVO-027) or not calibrated (SRVO-033) is telling you the underlying position data is missing or invalid. Treat those messages as the starting point, and correct the cause they point to rather than retrying mastering blindly.

Understand how the controller derives position

The current position comes from three pieces of data: the pulse count per degree ($PARAM_GROUP.$ENCSCALE), the pulse count at the zero-degree position stored by mastering ($DMR_GRP.$MASTER_COUN), and the current pulse count read from the Pulsecoder during calibration. Mastering writes the zero-position count; calibration, called positioning, reads the live count and recognizes where the robot is. If any of these is wrong or lost, calibration will not resolve to a valid pose.

Check the encoder battery circuit first

A dead or disconnected Pulsecoder backup battery drops absolute position data, which is a frequent reason mastering will not hold. A BZAL alarm (SRVO-062) means the backup battery is empty or its cable is broken; a low-voltage BLAL warning (SRVO-065) means the battery is failing and should be replaced while power is on before data is lost. Replace the battery in the base battery box and check the internal power cable to the Pulsecoder for a disconnected or grounded conductor.

Caution: If a BLAL warning is present, replace the battery promptly while system power is on. Letting it progress to BZAL loses position data and forces a full remastering.

Rule out a rotation-counter or pulse fault

A rotation-counter fault (SRVO-063, the RCAL alarm) points to a Pulsecoder or grounding problem rather than a procedure mistake. Check that the earth cable between the controller and the robot is securely landed on the grounding plate before assuming the encoder is bad. If the pulse count captured at power-off does not match the count at power-on, the controller flags a pulse mismatch after a Pulsecoder or battery change, which also requires remastering.

Clear a Pulse not established warning before mastering

Mastering cannot run until each axis has rotated enough to establish a pulse, and the controller enforces this with the Pulse not established warning (SRVO-075). Reset the warning, then jog the affected axis roughly one motor revolution until the same warning stops recurring. This condition normally appears after a BZAL event, and it has to be cleared before any mastering method will accept the axis.

Caution: Do not attempt to write mastering data while a Pulse not established warning is still active on an axis. Establish the pulse by jogging first, or the result will be invalid.

Recover from a Pulsecoder alarm correctly

For battery-loss and pulse alarms, correct the physical cause, then perform the Pulsecoder reset (RES_PCA on the Master/Cal screen, or the PULSE RESET operation) and cycle power. After a BZAL is fixed the manual has you set $MCR.$SPC_RESET to TRUE and power up again, after which mastering is required. Never clear these alarms and run production without redoing mastering, because the position the robot reports would be untrusted.

Enable the Master/Cal screen

The Master/Cal screen stays hidden unless system variable $MASTER_ENB is set to 1 or 2, a deliberate guard against accidental mastering. Set it on the system variable screen, then navigate MENU, 0 NEXT, 6 SYSTEM, F1 [TYPE], and select Master/Cal. After you press F5 DONE at the end of mastering, $MASTER_ENB returns to 0 automatically and the screen disappears again.

Caution: Mastering by mistake can make the robot move unexpectedly and is dangerous. Enable the screen only when you intend to master, and confirm the correct group and axes first.

Confirm the torque and brake state on screen

At the top of the Master/Cal screen, note the TORQUE state so you know whether the axes are held. When a method needs the arm moved to a reference, use the manual brake control screen to release the relevant brake, and restore it afterward. Before releasing a brake, mechanically block or support that axis so it cannot drop under gravity once the brake is off; keeping clear is not a substitute for physical support, and this is a qualified-technician step.

Inspect the reference the chosen method depends on

For fixture position mastering, confirm the jig or dowel pins seat cleanly and are not worn, bent, or fouled with debris, since this factory method relies on the special jig for accuracy. For zero position mastering, confirm the zero-degree witness marks on each axis line up. For quick mastering, confirm the stored quick-master reference points still exist, because that method reuses reference points set in advance.

Jog each axis to the mastering position cleanly

Jog every axis by hand to the required mastering position and confirm nothing obstructs full travel to that point. For quick mastering of a single axis, the axis must sit within half a motor revolution of its reference position for the result to be valid. Verify the ACTUAL POS and REF POS columns agree before executing.

Caution: Never force an axis past resistance to reach a mastering position. Stop and investigate the obstruction, because forcing it can damage the arm or produce false mastering data.

Execute the mastering method

Select the intended row (for example 2 ZERO POSITION MASTER or 5 SINGLE AXIS MASTER) and confirm with F4 YES, watching for the Robot Mastered message and the returned mastering data values. In single-axis and quick single-axis screens, set SEL to 1 on each axis to master and 0 on the rest, then press F5 EXEC. A successful axis flips its ST status from 0 (data lost) to 2 (mastering complete).

Run CALIBRATE to complete positioning

Mastering alone does not finish the job; select 7 CALIBRATE and confirm with F4 YES so the controller reads the current pulse counts and recognizes the position. Alternatively, cycling power performs calibration on every startup. Watch for the Robot Calibrated message and sane current joint angles before trusting the result.

Verify the result and press DONE

Confirm the reported joint angles match the physical pose, then press F5 DONE to store the state and let $MASTER_ENB reset to 0. Cross-check the new mastering data against the factory record for the robot serial number where you have it. Only then move the robot at reduced speed to confirm it tracks correctly.

Caution: Do not return a robot to production on an unconfirmed or partial mastering result. Verify the pose and repeatability at reduced speed first.

What can go wrong: the Master/Cal screen is missing

If Master/Cal never appears under SYSTEM, $MASTER_ENB is still 0, which is its normal resting value after any prior mastering. Set it to 1 or 2 on the system variable screen and reopen the menu. This is expected behavior, so there is no fault to chase beyond re-enabling the screen.

What can go wrong: quick mastering reference points are gone

Quick mastering and quick single-axis mastering both need reference points that were stored earlier, and those points are lost when mastering data is lost through mechanical disassembly or maintenance. When the reference is gone, quick mastering cannot restore the robot, so fall back to jig (fixture) mastering or zero-degree position mastering to rebuild the base data. After that recovery, re-store the quick-master reference with SET QUICK MASTER REF for future use.

What can go wrong: gravity compensation blocks single-axis mastering

On robots with gravity compensation enabled, a confirmation popup asks you to verify the payload data is set correctly before mastering will run. If it reports that mastering cannot execute one axis at a time, select all unmastered axes and master them together in one operation. Where reaching every reference at once is impractical, perform a tentative mastering at an arbitrary position or at zero degrees first, then repeat accurately at each reference.

What can go wrong: not-mastered or not-calibrated persists

If the robot still reports it is not mastered (SRVO-027) after you master it, the stored adjustment did not complete or is invalid, so recheck whether the mastering data you wrote is actually valid and redo it. If it reports it is not calibrated (SRVO-033) when you try to set a quick-master reference, supply power and set up the reference point from the positioning menu in the correct order. A ref-position-not-set condition means the quick-master reference simply was never stored.

Escalate a suspected encoder or motor fault

If battery, cabling, grounding, fixture, and procedure are all confirmed good and mastering still will not hold, treat it as a Pulsecoder or motor hardware fault. Capture the alarm history and mastering data, then involve the manufacturer's service support rather than repeating the attempt. Keep the robot out of production until the root cause is corrected and mastering is verified.

Caution: A robot with incorrect position data can move abnormally and injure personnel or damage equipment. Correct the cause and confirm mastering before restoring any automatic motion.