The new DUAL FAN UNIT replacement for the Kenwood TS940S transceiver

This board is a aftermarked replacement for the original power supply fan, developed as a silent replacement for the original fan to improve the ventilation of the power supply.
The DUAL FAN UNIT 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.
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.
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).
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.

The fans used in this kit are standard size, so they are readily available and easy to find on the market as replacement parts.
The power supply 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.

Each DUAL FAN UNIT is shipped as preassembled and tested.

"TS940S FAN UNIT" Project webpage