[Elecraft] KS3 internal 100 watt amp (K3S/100) is intermittent

[Joe DeVincentis]

Could it be overheating? Or is the temperature calibration is out of whack. 

Joe,
KO8V

> On Aug 1, 2019, at 10:16, Richard Hoffman, K1DJ via Elecraft <elecraft at mailman.qth.net> wrote:
> 
> Rig:  K3S (100W with internal ATU), s/n 11064, P3, KPA500, KAT500, into SteppIR 3-el with 30/40 loop or wire dipoles/inverted-V's.
> 
> Problem:  My K3S 100 watt internal amplifier unit (K3S/100) has become intermittent.  
> 
> It first happened yesterday while I was running 100W on FT-8.  [I have done this hundreds of times, sometimes for lengthy periods, over the past 18 months with no problems.]
> Suddenly, my power output dropped to zero, and my received signals audio and P3 display also suddenly went quiet.   
> 
> After some fiddling around, I figured out that if I reduced the K3S power to 10-12 watts, both transmit and receive came on again — leading me to conclude that it must be my 100W amp unit that had dropped out.  
> 
> I rebooted the rig and the 100W internal amp unit kicked back on.  So I was hoping I had just triggered a protective circuit which had reset.   The rig worked fine at 100W for a subsequent hour-long multi-band CWOPs CWT CW session at 100W.  Then, however, a few minutes into the next CWT session hours later, the same thing happened again.  Power output suddenly dropped from 100W to 0, and received audio and a P-3 screen filled with many medium to strong CWOPs signals simultaneously went quiet.  
> 
> I reduced the power on the K3S down to 10W, and both transmit and receive worked again, but only at low power.
> Please pass along any helpful suggestions, and thanks!
> Richard Hoffman (Rich), K1DJScituate, MA