In preparation for the SOTA 12 metre challenge I needed to fix a low TX power problem with the FT757 on 10 and 12 metres. I had previously noted that one of the coils on the low pass filter board had been damaged from getting hot, too hot.
I had used the rig on 10 metres since then and the output was normal but just a few months ago it had dropped to about 3 or 4 Watts. When I removed the aluminium shield from the RF PA section I found that the coil had become fully detached from excess heat. I removed the existing wire from the toroid and wound slightly larger wire on for the same number of turns. I also replaced two wires that had been burnt as well.
Once the radio was reassembled I tried it out and found it was not running full power, only 50 Watts.
This is better than it was so I am happy for now and I’ll take another look at out when next I have a couple of hours to spare.
I also need to work out why the coil got so hot on the first place.
73