Diagnosing Intermittent Emergency Stop Trips

Read the alarm history to identify the exact ES source

On the teach pendant press MENU, select 4 ALARM, then press F3 HIST to open the alarm history screen. Each stop is logged as a specific SRVO code with a timestamp, and RESET events are logged between them so you can see the sequence. Press F5 DETAIL on a highlighted entry to read the full cause and remedy text.

Match the code to one of the emergency stop devices

The controller separates the ES sources: SRVO-001 is the operator panel button, SRVO-002 is the teach pendant button, SRVO-003 is the deadman switch, SRVO-004 is a fence open, and SRVO-007 is the external emergency stop input. Reading which code repeats tells you which physical circuit to trace before you touch any wiring.

Confirm the trip is real by correlating timestamps

Compare the logged timestamps against production events such as shift changes, a nearby drive or press starting, or a specific process step. A trip that always lands at the same moment in a cycle points to mechanical or electrical stress at that moment. A trip that clusters when a large motor nearby starts points toward induced noise or a supply disturbance.

Rule out a blown emergency stop board fuse first

If SRVO-001 appears together with SRVO-213, treat it as a fuse fault rather than a pressed button. SRVO-213 means fuse FUSE2 on the emergency stop board has blown or that no voltage reaches EXT24V. Check FUSE2 and confirm 24 V is present between EXT24V and EXT0V of the terminal block called out in the Controller Maintenance Manual.

Caution: A blown safety fuse is a fault to find and correct, never to bridge or oversize. Replace it only with the rated part after you locate why it opened.

Inspect the operator panel emergency stop button

For a repeating SRVO-001, open the operator panel and check the mushroom button contact block for a cracked housing, a loose spade terminal, or a contact block backing off its mount. Vibration can loosen the block enough to open the contact intermittently while the button is never pressed. Confirm the button twists cleanly to release and that the contact seats fully.

Inspect the teach pendant button and deadman path

For a repeating SRVO-002, check the teach pendant emergency stop button and its cable strain relief, since a flexing pendant cable can open the contact momentarily. For a repeating SRVO-003, the three position deadman was released or pressed too hard; confirm the enable switch and the operator panel mode switch are in the correct positions. If the pendant is the confirmed source and the contact is failing, replace the pendant.

Trace the external emergency stop chain wiring

For a repeating SRVO-007, follow the external button loop to the emergency stop board. The external buttons land as two channels: EES1 to EES11 and EES2 to EES21. Check every terminal in that loop for a screw that has backed out and every remote button for a loose or corroded connection.

Check the safety fence circuit terminals

For a repeating SRVO-004, the fence or gate circuit opened. The fence limit switches wire as two channels to EAS1 to EAS11 and EAS2 to EAS21 on the emergency stop board. Inspect the gate switch actuator alignment, since a switch that only just holds closed can drop out with door slam or frame flex.

Look for induced noise on long unshielded runs

Where the trip correlates with a nearby variable frequency drive or contactor, check that the emergency stop conductors are not routed alongside high current cables for a long parallel run. Coupled noise on a long run can momentarily look like an open contact to the safety circuit. Reroute the safety wiring away from the noise source and confirm shields are terminated as the diagram specifies.

Inspect quick-disconnect connectors for vibration damage

Walk every connector in the identified channel and check for pins that have backed out of the housing, spread sockets, or green corrosion. A pin making marginal contact opens under vibration and remakes when the cell settles, which is the classic intermittent signature. Reseat, clean, or replace the suspect connector.

Test each channel of the dual-channel device

Emergency stop devices use two independent channels, so a discrepancy between them flags a sticky or slow contact on one side. With lockout applied, measure continuity across each channel of the suspect button or switch while operating it by hand several times. A channel that reads open intermittently under light finger pressure is the failing element.

Set a monitor DO to timestamp future trips

To catch a rare trip, use the Signal to set if E-STOP setup so a chosen digital output turns on whenever a TP, external, or operator panel emergency stop is applied. Setting 0 disables it, and after any change the controller power must be cycled for it to take effect. Wiring that DO to your PLC or a data logger gives you an external timestamp to correlate with cell events.

Correct the identified fault at its source

Repair or replace the failing button, switch, connector, or fuse, or reroute the cabling as the investigation indicated. Tighten every terminal you disturbed to the specified torque and dress the cable so it does not chafe or flex at the failure point. Address the actual cause so the safety function stays fully intact.

Recover the cell the correct way after the fix

Rotate the pressed emergency stop button clockwise to unlock it, then press RESET on the teach pendant or operator panel. The alarm message clears from the screen and the FAULT lamp goes off when the circuit is healthy. If the alarm will not clear, the cause is still present and the circuit is doing its job.

Monitor over several days to confirm the fix

Leave the monitor DO in place and track the alarm history over the following shifts. Because RESET events are logged alongside stops, you can confirm no new SRVO-001, SRVO-002, SRVO-004, or SRVO-007 entries appear. Only close the job once the intermittent pattern has fully stopped.

What can go wrong: the alarm will not reset

If the emergency stop alarm cannot be cleared with the button released and RESET pressed, the fault is still active somewhere in that channel. For SRVO-003 verify the deadman middle position and the mode and enable switch positions, and for a fence or button code re-trace the wiring for the open. Do not attempt to force the cell to run past an unresolved safety alarm; find the open first.

Caution: An alarm that refuses to reset is protecting you. Escalate to a qualified technician and correct the cause rather than searching for a way around the stop.

What can go wrong: SRVO-001 that is really a fuse

An operator panel e-stop code with no button pressed is a known trap when it appears with SRVO-213. On affected older software versions the fuse message can even point at the wrong board, so check the emergency stop board fuse and, if noted for your version, the additional safety I/O board fuse. Correct the fuse fault and its underlying cause before assuming the button itself failed.

What can go wrong: axis slips slightly at the stop

When servo power drops on an emergency stop, an axis can slip a small amount as the brakes set. If the robot was at a taught point, that small shift can post a position related alarm on the next run. Abort the program, jog the robot back onto the taught position, then resume so the recovery starts from a known posture.