EBMpapst Fan Motor Repair Advice Needed - Page 1
Forum section: electronics / repair

author: Shay
author_rank: Regular Contributor
timestamp: August 12, 2025, 07:19:54 pm
content: Hello,I am trying to repair a brushless motor with Hall-effect sensors.Although I have successfully repaired close to 50 of these motors, this particular one has made me suffer mentally.The issue is that it will only start at specific rotor angles. At other angles, it tries to start but then ends up blinking an error on the LED indicator. The blinking indicates a general error — the motor tries to start but does not receive the expected updates from the Hall sensors.Even when it does start at certain angles, the startup is sluggish and feels like the motor is binding. I will share a video on my Google Drive so you can see what I mean. Once it’s running, it operates absolutely smoothly and without issues.I checked the Hall sensor signals and they appear fine, but just to be sure, I replaced them. The issue remains. The rotor is connected directly to the PCB via sockets, so incorrect wiring is not possible.The startup sequence is handled by the MCU, but since the motor runs fine at specific angles, I don’t believe the MCU is damaged.I’m looking for your advice on how to proceed with the repair.Thanks a lot.https://drive.google.com/file/d/132yHau874EZK2SiEoryBQWmWuE5aFMq-/view?usp=sharing

author: DaJMasta
author_rank: Super Contributor
timestamp: August 12, 2025, 07:45:06 pm
content: Are the hall effect sensor outputs buffered or conditioned by anything before the MCU? Is the part they are sensing any different, more distant, or partially incomplete than on the others?If I were to guess, the MCU is sensing missing pulses and is altering the startup timing because of it, but I can't say for sure.Is there any current sensing? If there is binding somehow (a bearing issue?) and current is being sensed, it could be that the controller is noticing the extra starting current and changing the way it starts.

author: amyk
author_rank: Super Contributor
timestamp: August 13, 2025, 05:11:42 am
content: If a brushed motor doesn't start in certain positions it's normally a sign of a bad winding or commutator section. If a brushless motor doesn't, it could be a dead phase. Have you tried measuring the resistance of all the phases?

author: Shay
author_rank: Regular Contributor
timestamp: August 14, 2025, 07:47:57 pm
content: Quote from: amyk on August 13, 2025, 05:11:42 amYes I did. I measured inductance and resistence. Inductance was 100mH between the windings and resistance was about 1.2 ohm.Quote from: DaJMasta on August 12, 2025, 07:45:06 pmI'll have to confirm but I remember the hall effects output to go through series resistors, protection diodes and some light filtering to the MCU.As for the position of the hall effect on the rotor itself, i will check and see if there is something special on those angles.There is current sensing, I'll check with my scope the Voltage on the sense resistor and compare that with a working motor, to get some clues on what's happening.Thanks for the suggestions. I will update back.

author: motor-guy
author_rank: Newbie
timestamp: August 25, 2025, 05:27:36 pm
content: The motor works fine after startup because it probably switches to sensorless operations.QuoteDo you mean hall effect on the stator? And yes, the controller's outputs vary with the position of hall sensors with respect to the coils. If the hall effect sensor is on the center of the stator-tooth of phase/coil vs if the hall effect sensor is between two stator-tooth, the output switching to the motors will be different.QuoteSince you have a scope, rotate the motor by hand and check the voltage on the hall effect processing circuit just before the controller pins. This should be a nice clean square wave (most likely 5V). If it is not, your PCB is likely damaged. Work backwards from there till the hall effect inputs from the motor.

author: Shay
author_rank: Regular Contributor
timestamp: September 02, 2025, 09:24:17 pm
content: Quote from: motor-guy on August 25, 2025, 05:27:36 pmAll the hall sensors are nice clean square wave directly to the MCU. not only that, I can spin the rotor by hand and it does not throw an error on the motor - if I disconnect one of the series resistors from the halls to the MCU, and I spin the shaft by hand, it throws an error related to the halls. so the MCU is checking for the hall effect sequence and if something is off it blinks error led. so I am fairly confident it is not related to the halls.I also tried different rotors that are working ok on other boards and it is the same issue. so it is also not related in any way to the rotor itself.

author: motor-guy
author_rank: Newbie
timestamp: September 18, 2025, 03:22:18 pm
content: I've seen only 2 reasons why motor don't work with hall sensors:1. The controllers have HA,HB,HC and A,B,C labels. The motors also have these labels or they are color coded (Hall A and phase A are the same color). You need to match the phase A of the motor to phase A of the controller and hall A of the motor with hall A of the controller. If you don't match them right, the motor won't spin.2. The hall sensors are displaced from their actual position in the stator. In this case, the hall signals will look right and the controller will also think its the right signal but the motor won't spin. The hall sensors need to placed at exact positions in the stator.Both of these situations give square wave sequence that are expected from a hall sensor but the controller can't interpret and switch the correct phase.From your answers, I think it is just a bug in the connections. If you don't have the labels, you can try all combinations of connections (there are 36 possible combinations I think).