100 watt problem

[Paul-288]

Dear Board Members,

My Elmer and I are having a problem trouble shooting My K2 with the 100 watt option.  Right now the the basic K2 is working
fine on QRP and the 100 Watt option is on my Elmers workbench.  I gave up on Sunday and left the
100 watt option with him and this morning the following email hit.  I wanted to post it and see if any
others have had any problem similar to this or maybe someone can give additional assistance with this problem.  FYI this rig has run continuous 24-7 for one and a half years
without any major problems and it has been hooked up to a 30L1 for about 6 months prior to any of this trouble.





Was up to 1:30a.m. last night. Concluded that you have no power control.
Possibly cause is no ALC in the amplifier or, high SWR fro bad filters
and/or T-R switchinng failures. I checked the  T-R switching and all the
filters...all seems OK. However, the ALC doesn't seem to be working. This
causes the amplifier to "run away" with itself and the microprocessor has
no control.

Your power sense(SWR) circuitry not only provides Forward and Reflected
power readings to the processor for metering, it also takes part of the
forward power voltage,buffers and amplifies it, and sends it to the
processor for use in developing ALC. The processor then figures out how to
adjust the power output based on this voltage. Also, It also looks at these
voltages and does things to protect the finals. The desigantion of this
voltage on the schematic is VRFDET. Without this voltage(or an incorrect
value) the processor doesn't know how to adjust the power output. So, it
runs a full QRP(20 watts) or a full QRO(100watts or more) depending on the
setting of the power output control. This lack of power control would
explain your abnormal heating as well. I checked one of the OP AMPS in this
part of the circuit and it does not act normal. It feeds another OP AMP
which delivers the VRFDET voltage to the main processor  in the K2. That is
where my head hit the table and I had to quit.

Tonight, I will set up my amplifier and take readings of the VRFDET voltage
at different power settings. That will give me an idea of what to look for
in your amplifier. I will then know if my theory is correct or this is
another dead end.  To understand it thoroughly, you have to
know details about how the processor thinks about ALC. So that is where we are
at.

If you have time, surf the archives for people with no power control after
they hooked the K2 to a big amp. I have a hunch that if I find the VRFDET
voltage and/or circuitry bad,  that it was caused by high SWR from your
Collins amplifier input at high power. The detector and OP AMPS that form
this VFRDET voltage is right in your output. So, high SWR(at high Collins
power) at this point can do some damage causing loss of  power control and
possibly also damaging the finals.






Any ideas would be appreciated.

Thank You
Paul
K8QT
#3479
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