[ICOM] PRO III and shut down

[hamop]

    Hello all ... need some assistance. Never had this situation happen before. Today while operating on 20m CW I noted no output, well maybe 5 watts, and I thought maybe the PS125 had blown an internal fuse for some reason. I was running about 50 watts to a Titan amplifier at the time, my main setup for 3 years now. Well, rather than tear into the PS125, I put a PS85 in line and again a full 100 watts immediately. So thought the PS125 had truly blown a fuse. Well, after another shutdown to about 5 watts I thought the PS85 had also blown a fuse. 
   As one last effort, after about 5 minutes, I returned on the PS125 and PRO III and a full 100 watts output again. I found out that if I turned on the rig and did NOT hook the PTT line to the Titan, all seemed to be OK with no “shut down”.  But, even keying the amp with an EXTERNAL foot switch and trying to drive the amp, bang ... again just 5 watts out, but it returned to 100 watts after another 5-6 minutes.  Is the PRO III or PS125 and PS85 ( unusual for both to do it) heating up inside causing the shutdown by some quirk feedback from the Titan amp?  Seems like if just barefoot straight to the antenna, I can transmit 100 watts as normal with NO shutdown. Puzzling to me for sure. Appears since same thing happened to the PS 125 and 85 that both should not have developed the same ‘shut down’ issue. That leaves me wondering if my PRO III finals are overheating some how?
  Thanks for any suggestions.  Receive is fine the entire time. If I shut down the PS and PRO III for just 3-4 minutes, the output may drop quickly with about 20 seconds of CW and the longer units are off , the longer the power stays up.
73
San K5YY