Repair experiences of some laboratory centrifuges

This page may help technicians and repairers solve common problems with some laboratory centrifuges. (Warning: untrained personnel should not attempt to repair this equipment due to the risk of electric shock from high voltages inside. Also, be cautious of biological and chemical contamination: the rotors and the inside of the centrifuges may be contaminated with bacteria, viruses, human fluids, DNA, RNA, and toxic substances.)

Beckman Allegra 21R Centrifuge Repair

Problem Encountered

The Beckman Allegra 21R centrifuge was not reaching an adequate speed: the rotor started spinning, but did not exceed 100-200 RPM. No errors were displayed, making it difficult to diagnose the problem. This type of defect is related to a motor speed sensor that does not send correct data to the circuit board, preventing the rotor speed from being controlled.

Solution

The cause of this malfunction is the magnetic cylinder (similar to a ball bearing) at the bottom of the motor shaft, which communicates the motor speed to the control board via a magnetic field sensor. This magnet can detach from the motor shaft or remain attached but rotate freely, preventing the sensor from properly detecting the speed. Here are the steps to fix the problem:

Beckman Allegra 21R Centrifuge
Click to enlarge image
Beckman Allegra 21R Centrifuge
Click to enlarge image
  1. Turn off the centrifuge and disconnect it from the power supply.
  2. Remove the front panel by unscrewing the 5 screws holding it in place. This will give you access to the inside of the machine.
  3. Beckman Allegra 21R Centrifuge
    Click to enlarge image
  4. Examine the bottom of the motor shaft: by looking through the open panel, you can see the bottom of the motor where the small magnetic cylinder is located.
  5. Beckman Allegra 21R Centrifuge
    Click to enlarge image
  6. Inspect the magnet: the magnetic cylinder may have detached or be spinning freely on the motor shaft. This magnet is crucial for the motor's speed sensor to function.
  7. Beckman Allegra 21R Centrifuge
    Click to enlarge image
  8. Clean the magnet and shaft: use a solvent to remove dust, oil, and other debris from both the magnet and the motor shaft. This ensures the magnet adheres properly.
  9. Secure the magnet: apply strong adhesive to the magnet and reattach it to the shaft.
  10. At this point, it is advisable to clean the inside of the centrifuge by blowing air. It may also help to disconnect and reconnect each electrical connector to ensure electrical contacts are secure. In the previous image, an arrow points to a nut I found loose, so it's recommended to check the fastening of nuts subjected to stress and vibration. Reassemble the front panel and test the centrifuge.

Problem Encountered

In another Beckman Allegra 21R centrifuge, error 28 appeared on startup, and sometimes the "notA1" error also appeared on the display. Despite attempts to reset using the control panel (pressing the following key combinations: press the up arrow once, press Enter twice, press Enter a third time and hold until the menu appears on the display, scroll through the menu with the arrows to select the reset option), the error kept reappearing. However, the problem turned out to be the same as the magnet issue we just described.

Additional Steps to Resolve Error 28

  1. Follow all the procedures listed previously to check and secure the magnet. Disconnect and reconnect all electrical connectors (sometimes, false contacts due to oxidation of the pins are the cause of problems).
  2. In my case, the error persisted, even after resetting from the panel again. I solved the problem by leaving the centrifuge on for about half an hour. Perhaps this allows the system to "self-repair." I then performed the reset procedure again and this time, the error did not appear. I immediately set the rotor type and everything worked again.
  3. Centrifuga Beckman Allegra 21R
    Clicca per ingrandire l'immagine

Eppendorf Centrifuge 5415D Repair

Problem encountered

The Eppendorf 5415D centrifuge was displaying error 17. After consulting online resources such as https://staff.washington.edu/wbeaty/chem-eppndrf.html and https://www.labwrench.com/thread/219547/resolving-error-17, it was determined that the problem was with the electrolytic capacitor near the UC2844 IC. In some cases, the capacitance of the capacitor may decrease under voltage, even though the capacitance meter does not detect any apparent defect.

Solution

Here are the steps to follow to resolve error 17:

  1. Unsolder the 22μF (microFarad) electrolytic capacitor and replace it with one of the same capacity or slightly higher capacity. In my case, after unsoldering the capacitor I checked it with a capacitance meter and its capacity was identical to that declared so it did not seem broken. However, proceed with the replacement anyway because under load this capacitor does not work.
  2. Solder the new capacitor with a small tip soldering iron and be careful not to overheat the board because the SMD components around it could come off. In my case, error 17 was solved.

Problem with encoders

Later, I noticed that the encoder knobs were slightly stiff, and sometimes the time and speed values ​​on the display would change by two steps at a time with each click of the encoder. Sometimes the clicks of the encoder would not cause any change in the digits on the display. I replaced the encoders and the problem was solved. When I took the broken encoders apart to see what the internal problem was, I found that the rubber parts inside the encoders had degraded, like rotted and fragmented. A word of warning: do not use any spray or deoxidizer for encoders because the solvent that gets inside can swell or deform the rubber parts.