[Elecraft] new K1: 2W out, no more, CPU bug or ALC problem?

[Wallace, Andy]

Hi, Folks. My dad is finishing up a 2-band 40/20 K1, rev 1.09 firmware and
serial 12xx. This is the new main board rev also. 

The K1 is operating properly -- BELOW 2 WATTS output!

Symptoms are:

1) You can set OUT to 5.0 but transmitting only yields 2.1 or so on 40m.
This
was confirmed on an OHR external wattmeter. The display only shows two bars.
Going back to OUT shows 5.0 remains. 20m yields only a watt. 

2) Below 2.1W or so, the rig behaves normally. You can set the power to 0.3W
and
see about 0.3. 1W is 1W. 

3) Pressing the two TUNE buttons also yield 2W out. While in tune mode,
pressing
the + and - buttons has NO effect. You can't turn it up OR down. 

4) In troubleshooting with him today, checks with an RF probe as described
in
the manual show many signals being off -- part of that could be due to the
fact
we can't get 5W out and that's what the voltage readings should be made at. 
We noticed that the (transmit) ATTN test point read low, and checked D18, a
1N4007. 
It was completely open!  He substituted a silicon diode temporarily and we
continued to look around...

5) The POWER signal going into the same transmit attenuator circuit is
behaving
strangely. This comes from the front panel board, the MAX518 D/A converter
at
U2. Now...here is a great piece of evidence...the POWER signal was
approximately
5.8 volts (I believe) with OUT set to 5.0W. Setting OUT to 2W also showed
the
same level on POWER. Going down to 1W, POWER did drop to less than 4V or so.
So
the interesting thing is that the POWER SIGNAL REACHES A PLATEAU AT 2W AND
CAN'T
MAKE IT ANY HIGHER. 

My gut feeling is there is something wrong with the MCU, which feeds this
D/A.
Ideas? Does this sound plausible? Everything else appears to operate
normally,
receive and transmit seem to work fine otherwise. 

If it's not the CPU, could it be something which blew D18? What would cause
that? Sure looks like the problem is in the transmit attenuator/ALC
circuits. 

Any help appreciated! 

-Andy