Ham Radio ICOM IC756 PRO – II – III / PS125 Fan Modifications

The Experiment: In this experiment were going install an external cooling fan on the ICOM IC756 PROIII to minimize the heat on the chassis, then will perform a fan modification on the ICOM PS125 power supply to minimize the fan noise.

Table of Contents

1. ICOM IC756 PRO – II – III External Cooling Fan
2. ICOM PS125 Noisy Fan Modification
3. Prototype
4. Notes
5. Conclusion
5. Credits

ICOM IC756 PRO – II – III  External Cooling Fan:

Decided to install an 80mm x 80mm external cooling fan on the IC756 PRO – II – III to cool the rig down, did not want to open the radio to install the OZ1DB IC756 PROIII fan mod. Used a 5.1v zener diode and a 15 ohm resistor to adjust the fan speed. Powered the external fan from the Tuner Control Socket. See photos below…

The external fan runs at an unnoticeable low speed all the time and keeps the ICOM IC756 PRO – II – III very cool. The internal fan still comes ON, on TX as it should.

Update: A simple mounting bracket for the IC756 PRO – II – III external fan, which does not require any modes made to the radio.



ICOM PS125 Noisy Fan Modification:

To reduce the ICOM PS125 fan noise used, the PS125 fan mod posted on  OZ1DB website, did make a slight change, used a 5.1v zener diode and a 270 ohm resistor in series with the zener diode to adjust the fan speed.  To keep from having to remove the PCB, Connect the cathode of the zener diode to  pin3 back wire on fan plug, then grounded the resistor to pin2 black wire led plug. See photos below…

The fan in the ICOM PS125 now runs at a unnoticeable low speed all the time and should go into high speed when the temp gets to high.





Different brand of cooling fan require, different  resister values to set the fan speed.



This was definitely a worth while experiment. The ICOM IC756 PRO – II – III external fan installation definitely keeps the rig very cool and the ICOM PS125 fan mod definitely improves the noisy PS125  fan issue.

I have been using the fan modes for  some time on the ICOM IC756 PROII – PROIII / ICOM PS125. The radio never gets hot and hardly ever hear the ICOM PS125 fan come on to full speed.



1. ICOM IC-756PRO3 fan modification / ICOM PS-125 fan modification