For PROFIBUS:
For PROFINET:
| Root Cause | Solution |
|------------|----------|
| PLC in STOP | Set PLC to RUN or reconfigure drive to ignore missing telegram (p2040 = 0 – not recommended for safety) |
| p2040 too short | Increase p2040 to at least 2–3× bus cycle time |
| Loose connector | Reseat or replace bus connector |
| Wrong telegram type | Match p0922 with PLC configuration (e.g., standard telegram 1 for speed control) |
| No termination | Activate termination on both ends of PROFIBUS segment |
| EMI | Check cable routing, add ferrites, verify shield grounded at both ends |
| Faulty option board | Replace communication board (e.g., CBE20 for PROFINET) |
| Cause | Description |
|-------|-------------|
| PLC stop | Controller switched to STOP mode, stopped sending cyclic data |
| Cable issue | PROFIBUS/PROFINET cable disconnected, damaged, or poorly terminated |
| Connector fault | Loose or broken fieldbus connector (especially PROFIBUS 9-pin D-sub) |
| Configuration mismatch | Telegram configuration (e.g., telegram type, length) differs between drive and PLC |
| Bus overload | Excessive bus cycle time or high bus load causing intermittent telegrams |
| Parameter error | p2040 (telegram monitoring time) set too low |
| Master failure | Fieldbus master (PLC) power cycle or hardware fault |
| Interference | Electromagnetic interference (EMI) on bus cable | siemens drive fault code 7902
Fault code: 7902
Typical device family: Siemens SINAMICS / SIMODRIVE (frequency converters and servo drives)
Symptom: Drive reports fault 7902 and trips or blocks operation.
Likely meaning: Encoder feedback error or position feedback failure detected by the drive's encoder interface. The drive cannot reliably determine motor position/speed.
Common causes:
Diagnostic steps (ordered, concise):
Temporary workarounds (use only if safe and permitted): For PROFIBUS:
Preventive measures:
When to escalate to Siemens support or an authorized service partner:
Useful information to provide when requesting support: For PROFINET: | Root Cause | Solution |
If you want, I can draft a troubleshooting checklist tailored to a specific Siemens drive model (e.g., SINAMICS G120, S120, or SIMODRIVE) — tell me the exact model and motor/encoder type.
(related search suggestions provided)
Use a digital multimeter and, if available, a megohmmeter.