Recovering from a Failed Boot

Rule out power and hardware before assuming software

Confirm the controller has stable input power and that internal boards and cables are seated before treating the fault as a software problem. Lock out and tag out before reseating internal boards or cables; checking live input power is a qualified-technician task. Look at the seven-segment LED on the main board while you cycle power, since it reports how far startup gets.

Caution: If a board or cable is reseated, follow lockout/tagout and let a qualified technician open the enclosure. Do not probe inside a powered controller.

Capture the failure symptom

Power cycle the controller normally and watch the boot sequence for the exact point where it hangs or aborts. Note any message on the pendant and the state of the main-board seven-segment LED, because those two clues steer everything that follows.

Know the start modes you can choose

The controller offers hot start and cold start for normal running, plus controlled start and initial start for maintenance. Hot start restores the pre-power-down program state, cold start aborts the program and turns outputs off, controlled start brings up a simple menu that cannot move the robot, and initial start wipes everything. For recovery you work with cold start and controlled start.

Open the Configuration Menu

Hold the PREV and NEXT keys on the pendant, then switch the controller power breaker on. The CONFIGURATION MENU appears with 1 Hot start, 2 Cold start, 3 Controlled start, and 4 Maintenance.

Try a plain cold start first

From the Configuration Menu select 2 Cold start to bring the system up with power-failure recovery disabled. A cold start aborts the program, turns every digital, analog, robot, and group output off or to 0, and resets the feed override, so a hot-start data problem often clears here. If it boots cleanly, verify carefully and stop; you may not need a restore.

Boot into controlled start

If cold start still fails, hold PREV and NEXT at power-on and select 3 Controlled start. The controlled-start menu is a simple system that cannot operate the robot, but it can read system files and change protected system variables. This is the only mode from which system files can be read back in.

Confirm there is room in F-ROM for controlled start

Controlled start needs more than 600KB free in F-ROM, and the option is greyed out of the Configuration Menu if less is available. Check free F-ROM from the controlled-start select menu by choosing 0 Next, then 4 status, then memory.

Caution: If free F-ROM is under 600KB, remove unnecessary data from the FR: or FRA: device to make room before retrying. Do not delete files you have no backup of.

Inspect memory and system-file status

From the controlled-start menu press MENU and open the Memory screen to read memory status, then the File screen to see which system files are present. This tells you whether the fault is missing or damaged system data that a restore can fix.

Restore system files from the known-good backup

On the controlled-start File screen, connect the backup device and press F4, shown here as RESTORE, to read files back automatically. Selecting all of above on the file menu reads all files simultaneously, which is the fastest way to reload a full set. To switch F4 between RESTORE and BACKUP, press FCTN and choose RESTORE/BACKUP.

Reach an older backup version if the latest is bad

The file menu sees only the root directory, which normally holds the newest backup. To load an earlier automatic-backup version, press F4 CHOICE on the Loadable version item and pick a time; the selected version is copied to the root directory so you can then load it in the file menu.

Cold start and check the result

After the restore, press FCTN on the controlled-start menu and select 1 START (COLD) to bring the robot up. Confirm the controller now completes an ordinary start sequence without the earlier hang.

Restore a full image if file restore is not enough

If system files alone will not boot, restore a full F-ROM and S-RAM image by holding F1 and F2 at power-on to reach the Restore Controller Images screen. Pick the device (1 Memory card MC:, 2 Ethernet TFTP:, 3 USB UD1:, or 4 USB UT1:), navigate the directory selection menu with 0 Next and -1 Prev, and choose OK for the current directory. When the file count matches the module size, answer Y=1 to Restore image files.

Caution: Use only image files taken from a controller of the same F-ROM and S-RAM size. Restoring mismatched images can cause fatal damage to the controller.

Verify mastering and position after recovery

A restore can leave position data suspect, so open MASTER/CAL and confirm mastering is intact before any production motion. If the pulse count was lost, re-master; when a reference position was already set, Quick Mastering or single-axis quick mastering recovers it quickly.

Verify I/O, then run a reduced-speed test

Check that digital I/O responds as expected, since a cold start left every output off or at 0. Then run a full cycle at reduced speed and confirm normal operation before returning the robot to production.

What can go wrong: controlled start is not selectable

If controlled start is missing or refused from the Configuration Menu, free F-ROM is almost certainly below the 600KB threshold. Confirm free memory in the memory status screen, then clear unnecessary files from FR: or FRA: and retry.

What can go wrong: image restore refuses or the size mismatches

The restore screen compares the FROM and SRAM file counts against the controller's module size and only proceeds when they correspond. If they do not match, stop and locate the correct image set for this controller rather than forcing it.

Caution: Never continue an image restore when the module size does not match, because it can permanently damage the controller.

What can go wrong: the seven-segment LED shows 1 and memory is lost

If the backup battery voltage dropped too low, cycling power can leave the system unable to start and the main-board seven-segment LED displaying 1, meaning SRAM contents were lost. The fix is to replace the lithium memory-backup battery and reload data from your external backup, not to keep power-cycling. Lock out and tag out the controller's power before opening the cabinet to replace the battery.

Caution: Route battery replacement and SRAM re-entry to a qualified technician. Repeated power cycles will not recover lost SRAM, so correct the cause first.

What can go wrong: mastering is gone after the power event

If the pulsecoder backup battery was disconnected or empty, the controller loses absolute position and posts SRVO-062, and after a power cycle SRVO-075 reports that the pulse is not established. Restore the encoder battery supply, then re-master; with a saved reference position, Quick Mastering is the fast path back.

Caution: A low pulsecoder battery first shows as SRVO-065 warning; act on that warning before it becomes full position loss.

What can go wrong: a restore or backup was interrupted

If the controller is powered off partway through a backup, the files created during that session are deleted and the last completed version is restored to the root directory. Treat any interrupted transfer as incomplete, and reload from a version you know finished.