FANUC SRVO-218 External E-Stop / Servo Disconnect: TBOP Jumpers, Dual-Channel Wiring, and the Mate Cabinet Trap

You drag a used LR Mate 200iC out of storage, set it on a bench, and try to clear the alarms so you can master it after replacing a three-year-old battery. The cabinet keeps throwing SRVO-218 Ext.E-stop/ServoDisconnect, yet no e-stop button is pressed. The previous integrator removed the cell’s external safety system before scrapping it, and someone, somewhere, forgot to put the factory jumpers back. This exact scenario walks through the door at Probot Systems every few months, and the fix is wiring discipline, not a parameter.

This post is written for technicians and integrators recommissioning an R-30iA Mate or R-30iB Plus cabinet that no longer has its OEM external safety setup. It covers the TBOP jumper configuration, the dual-channel rules that catch people out, and the alarm-clearing sequence once the wiring is right.

What this error actually means

SRVO-218 is the alarm that fires when the controller cannot see a valid external e-stop or servo disconnect signal. The FANUC error code manual is direct on this one: “SRVO-218 Ext.E-stop/ServoDisconnect Cause: The external emergency stop signal or the servo disconnect signal is asserted. Remedy: 1. Release the external emergency stop signal and press RESET. 2. If the servo disconnect signal is used, release it and press RESET.” That entry is on page 1605 of the R-30iB error code manual, and the part operators miss is that “asserted” includes the case where one channel of a dual-channel input is floating because no jumper is in place.

On an R-30iA Mate cabinet, the external e-stop signal lands on TBOP-6 and TBOP-7. Both terminal blocks carry monitored dual-channel inputs. The controller continuously compares the two channels, and any mismatch outside its tolerance window posts SRVO-218 on the next servo enable.

Most common causes, in order of probability

In order of how often we run into each one on site:

1. Missing factory jumpers on a re-purposed Mate cabinet. This is the single most common cause we see. A user re-purposing an LR Mate 200iC with an R-30iA Mate documented exactly this scenario on Reddit, asking for the OEM TBOP-6 and TBOP-7 jumper configuration after removing the previous cell’s external safety system (reference thread). No jumpers, floating channels, SRVO-218 on every power-up.
2. Single-channel jumper bridging only EES1. Someone added a jumper, but only across one channel. The controller sees a mismatch and locks out. Dual-channel inputs are not optional on FANUC safety circuits.
3. External safety relay output stuck or worn out. On cells that still use an external safety PLC (PILZ, Banner, Sick), the output relay can stick or one of its channels can fail. From the cabinet’s point of view, SRVO-218 looks identical to a wiring fault.
4. Servo disconnect signal asserted unintentionally. Less common, but worth checking. Some Mate cabinet variants carry a servo disconnect line that, if accidentally jumpered to ground, throws SRVO-218 alongside the e-stop diagnostic.
5. Operator panel board fault. Last on the list because it is the most expensive guess. It happens, but only consider it after everything above has been ruled out.

How to diagnose in under 10 minutes

Step 1. Open the operator panel side of the cabinet. On an R-30iA Mate, this is the door with the mode switch and the cabinet e-stop. Locate TBOP-6 and TBOP-7.

Step 2. Pull the FANUC connection manual page for your cabinet variant before touching anything. The R-30iA Mate uses slightly different terminal-block labeling than the R-30iB Plus, and the wrong factory print will send you down a useless path.

Step 3. Confirm what is supposed to be connected to EES1, EES2, and the servo disconnect terminals. Any input not in use must carry the OEM jumper, not just a piece of wire bent across two screw terminals.

Step 4. With the cabinet off and locked out, meter continuity on each channel. Both EES1 and EES2 should read closed when no e-stop is pressed and no external safety output is open. Both should open simultaneously when an e-stop is pressed.

Step 5. If the cabinet was previously fed by an external safety PLC, trace every conductor back to its origin. A stray open wire still landed on EES2 is a textbook SRVO-218 generator. The Reddit recommissioning thread tracks this exact problem on a battery-replacement project (reference thread).

Step 6. Power up, watch the I/O monitor for the safety inputs, and confirm both channels toggle together. A channel that toggles on its own is your fault, regardless of what the panel print says.

How to fix it

The fix depends on where you are starting from.

If you are re-purposing a robot with no external safety hardware: reinstall the factory jumper kit on TBOP-6 and TBOP-7. Each EES channel needs its own independent monitored loop. On an R-30iA Mate, the OEM jumpers ship as a small bag of wire links. If they are missing, fabricate two independent jumpers, one per channel, not a single wire bent twice across both.

If you are wiring a real external e-stop button: use a dual-contact e-stop (two NC contacts). Run EES1 to one contact and EES2 to the other. No shared wires, no daisy chain across channels. The same rule applies to door interlocks and light curtains, with the dual contacts coming from a safety relay output.

If a previous external safety PLC has been removed: pull every wire that no longer goes anywhere useful. Leftover conductors landed on EES2 are the dominant source of SRVO-218 on second-life cabinets.

If both channels meter correctly and the alarm persists: cycle power once with the cabinet locked, then watch the I/O monitor on the next boot. If SRVO-218 still locks the cabinet with verified dual-channel wiring, the operator panel board is the next suspect.

For a battery replacement on a Mate cabinet that has been sitting idle: clearing SRVO-218 is a prerequisite for mastering. The Reddit thread above walks through exactly that prerequisite sequence (reference thread).

When to call a specialist

Call us when you have verified that both channels close, the wiring matches the factory print, and SRVO-218 still locks the cabinet on power-up. At that point the operator panel board is the suspect, and swapping it requires a controlled start and a panel calibration. Doing that on a bench while the customer’s production schedule waits is not a one-person job.

The same applies if you are bringing a Mate cabinet back into production and want documented safety integration. The factory jumpers are fine for proving the cabinet works, but they are not the integration an auditor will accept on a production cell.

Contact us for a recommissioning intervention, or set up a preventive maintenance contract so your safety wiring and jumper configurations are documented before the cell goes back into production.

Related errors to check

• SRVO-007 External Emergency Stop: same root-cause family on dual-channel safety inputs, with a different alarm code depending on which input opened. If both fire in the same cycle, the entire safety chain needs a wiring audit.
• SRVO-213 E-STOP Board FUSE2 blown: a blown fuse on the e-stop board can look like an open safety chain. Check the fuse before you start pulling wires.
• SRVO-220 SDI fuse blown: a separate failure mode, but on second-life cabinets where someone bypassed the safety circuit, a blown SDI fuse can show up alongside SRVO-218.

Probot Systems is a FANUC integrator based in Lévis, Quebec. We commission and recommission palletizers, welding cells, and machine tending cells across Canada and the US, and we have seen every variant of the TBOP jumper trap on R-30iA Mate cabinets. If your second-life Mate cabinet is throwing SRVO-218 and you want it cleared properly before mastering, let’s talk: contact us.