Old Dental Micro motor power supply problem

Thread Starter


Joined Jan 11, 2020

I have a very old Kavo Brand German made micro motor (probably made around 1970s-80s).

It it a very well built tool but the power supply is suffering from some problem.

When the brushed motor hand piece is connected and powered on, it will spin but in constant pulses (maybe 1 second on, 1 second off and so on).

When the hand piece is connected to a battery, it spins just fine, so I guess it is something wrong with the old power supply unit.

Could this be something as simple as an old capacitor, or something more complex?

I am not sure what type of power supply this is, but I will provide some pictures if anyone has any idea what could be causing this to happen.

Notice the array of contacts which is used to control the speed of the motor (very old).

Thank you!



Joined Jan 18, 2008
I would look at dirty contacts in that speed switch. That's easy to do and non-invasive. If you can figure out the switch sequence, you could try jumpering the connections and see if the problem persists. It looks like they may actually unplug. Are they in series? That is, if just one wire is removed/unplugged, does the motor stop?

Capacitors can go bad and replacing them to fix almost anything seems to be popular. The ones you show do not look bad in the pictures. Does the pulsing occur at all speeds?

Thread Starter


Joined Jan 11, 2020
I will have a look at the contacts see if they are dirty and also try to bypass them as mentioned to see if it still persists.
The pulsing happens at all speeds, the motor just has a bit more power with every set of contacts pressed.


Joined Jun 22, 2012
The CA324e is a quad op amp,,the white chips are 10K resistors in a chip with a common pin connection, chances are the op amp is a variable psu , ideally you need to draw it out to fix it or rebuild it.