select your language:


A state of the art replacement for the power supply fan on a Kenwood TS940S

Every owner of a TS940S transceiver knows the annoying noise of the fan at the back right of the power supply’s heat sink.
The cause of the noise is mainly the motor of the fan, which gets louder with age and hard to find as a new spare part:

The original power supply fan in a Kenwood TS940S (T42-0302-05)

Another disadvantage is the cyclic on/off switching of the fan, which is controlled by the AVR unit by a temperature sensor on the heat sink.

I have developed this fan unit as a silent replacement for the original fan and to improve the ventilation of the power supply:

TS940S FAN KIT front TS940S FAN KIT back

The new TS940S FAN KIT



The TS940S FAN UNIT is available from RF-SYSTEM‘s webshop.

Both fans on this kit are always active, but the speed is controlled automatically. Therefore two thermal sensors detect the temperature of the air flow and adjust automatically the speed of the fans accordingly with a temperature controlled linear voltage regulator.

To check the function of the fans, there is also a timer circuit that enables both fans at their maximum speed for a few seconds after the TS940 is turned on.

In addition, the minimum fan speed can be adjusted via a trimmer accessible through the slots on the heat sink cover, on the back side of the TS940 (see also the “FAN SPEED” labeled trimmer hole on the back side).

Is fixed with the four original screws through the holes for the original fan cover plate with the round cutout (which has to be removed), maintaining the original look of the heat sink cover.

The supply voltage (from 28VDC to 48VDC) for this dual fan assembly is taken directly from output of the main rectifier D101 where there is about 40VDC, mounted directly behind the heat sink:


The black (GND) and red wire (+40V) soldered on the fan unit should be connected at this points in the schematic:  supply

And here the final result: