After transmitting for approximately 2 hours at 50% duty with 150 watts output the temperature protection circuit activates reducing the output power to about 50 watts. Normally, full output power will be restored after the fans have had a chance to cool things down. Occasionally the power output will not return to normal, even after extended receive operations.
The temperature sensor is attached to the main transformer and is set to activate at 80°C. This setting was selected to reduce power before the internal fuse on the transformer opens.
After through testing, we have found that the temperature sensor should be set to 90°C to allow proper return to full power transmit. This setting will also allow the radio to be used at higher ambient room temperatures without worrying about the power output dropping in the middle of a QSO.
Qty Description Kenwood Part No. Circuit description
1 90°C Thermal switch S59-1416-05 S1
Caution: This modification requires soldering equipment rated for CMOS type circuits. It also requires familiarity with surface mount soldering techniques. If you do not have the proper equipment or knowledge do not attempt this modification yourself. Seek qualified assistance.
Time required for this modification is 30 minutes or less.