I would try to place the equipment in LOW and decrease with R4 which says that it is the adjustment of the low of 10W to 1W to see if it gives. This is if the information in the Service Manual that I obtained through the WEB is correct. View the image to see if it has these controls where they are indicated in the image. The other solution is to insert a 10 dB attenuator to convert excess power into heat. That is provided that the impedance of both TX and the device to be connected is 50Ω resistive.