[Kenwood] Hello / New to Net

[Pete Young]

Hi Everyone,
I am new to the net and this is my first posting.  I have a TS-850SAT that 
I bought new
about 6 years ago as a closeout.  I am very pleased with its performance, 
especially the
receiver, which is outstanding.  After using tube-equipped boatanchors for 
many years I've
developed the habit of keying the transmitter and tweaking the tuner, and 
although I have
been very careful not to do this with the '850. Still, I caught myself 
doing it a couple of times.
Now the '850 output is limited to about 25 watts on 80m, 50w on the higher 
bands.
Attempting to increase output power beyond this level is unsuccessful and a 
buzzing sound
appears on the carrier.  Is the cause a t/r relay problem, a PIN diode, or 
perhaps finals?
Anyone else have a similar experience?  Thanks and 73, Pete  K3IN