Code 21750: Error during output of cam switching signals via timer
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical Error during output of cam switching signals via timer alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Definitions: The signal output activated by the MD104 80 $MN_SW_CAM_TIMER_FASTOUT_MASK via the hardware timer (independent of the clock grid) did not work. Cause: interpolation cycle is greater than 15 ms. The alarm can be reprogrammed in the MD11412 $MN_ALARM_REACTION_CHAN_NOREADY (channel not ready). Reaction: Mode group not ready. Channel not ready. NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm. Channel not ready. Remedy: Please inform the authorized personnel/service departmen t. Shorten interpolation cycle (if at all possible). Program Continuation: Switch control OFF - ON.
Source: SINUMERIK 840D sl / 840Di sl / SINAMICS S120 Diagnostics Manual (DAsl, 03/2009)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Siemens SINUMERIK 840D CNC Alarms
Siemens controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 21750 on the SINUMERIK 840D CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Siemens's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4014 Siemens SINUMERIK 840D CNC codes.
Have a better solution?
Help the industrial community by sharing your repair experience for code 21750.
Need a searchable reference for more Siemens SINUMERIK 840D CNC manuals?
We structure equipment manuals into searchable code, title, cause, solution, safety note, and source-reference data. Send a PDF and example searched codes when you need public pages, private search, or structured exports.
Space reserved for Google AdSense / Industrial Affiliate Links
Monetization target for 2026