ABB IRB 140 alarm 37056 reports a fan that is stopped or rotating too slowly. In this case, replacing the driver-area and computer-room fans did not clear the alarm because the missing tachometer feedback came from a separate, smaller PC fan.
Confirmed symptoms and checks
| Item | Observed condition | Diagnostic meaning |
|---|---|---|
| Alarm | 37056: fan stopped or running slowly | The controller continued to detect missing or unacceptable fan feedback. |
| Driver-area fans | Two replaced and tested | Replacing these fans did not clear the alarm. |
| Computer-room fans | Two replaced and tested | Replacing these fans did not clear the alarm. |
| Fan supply | 24 VDC present | Supply voltage and fan rotation alone did not prove valid tachometer feedback. |
| Tachometer wiring | Continuity verified to control board A81 | The checked field wiring was intact. |
| I/O indication | Fan signals were absent from the displayed safety inputs | The controller was not receiving the expected status indication. |
Root cause
The fault originated at the PC's small fan, approximately 9 × 9 cm. The fan did not provide a tachometer signal. This device was separate from the two driver-area fans and two computer-room fans that had already been replaced and tested.
The case demonstrates the key diagnostic distinction: a fan can have 24 VDC and rotate while alarm 37056 remains active if its tachometer feedback is missing. Therefore, visible operation is not sufficient verification.
Troubleshooting procedure
- Identify every monitored fan in the cabinet, including the small PC fan; do not limit inspection to the driver and computer-room fan groups.
- Confirm 24 VDC at each fan and verify that each fan rotates.
- Check the tachometer signal from each monitored fan, not only cable continuity. Trace the relevant conductors to control board A81.
- Compare the measured tachometer result with the displayed I/O status. If wiring continuity is intact but the status is absent, isolate the individual fan that is not producing feedback before replacing A81.
- Correct the fan or tachometer-feedback fault and verify that alarm 37056 clears.
Board replacement decision
Do not conclude that A81 is defective solely because the previously checked fans operate and their cables have continuity. In the documented case, A81 was suspected, but the actual failure was the untested PC fan's missing tachometer signal. Evaluate the control board only after checking every monitored fan and confirming that each tachometer signal reaches the board.
FAQ
What causes ABB IRB 140 alarm 37056 when the main fans run?
A monitored fan can rotate yet fail to provide tachometer feedback. In this case, the missing signal came from the PC's small 9 × 9 cm fan.
Does 24 VDC at an ABB robot fan prove the fan circuit is healthy?
No. The checked fans had 24 VDC and operated, but alarm 37056 remained because another fan did not provide its tachometer signal.
Should I replace control board A81 for alarm 37056?
First check every monitored fan, including the small PC fan, and verify each tachometer signal through to A81. The documented fault was the PC fan feedback, not a confirmed A81 failure.