As John has pointed out, the problem can be anywhere in the KPA100
wattmeter circuit consisting of T4, C1, C95. R28, R29, D16, D17, R26,
R27, U5. R24. R25, Q10, Q11, and U6. With a bit more information and
some measurements that I can suggest, the field of suspect components
(and soldering thereof) can be reduced substantially.
73,
Don W3FPR
On 1/28/2014 3:31 PM, John Oglesby wrote:
Bill - I had this exact problem on my K2/100 during testing. Changing
C1 varied the power output, but the SWR was fixed at 9.9-1. The
problem was a short between the output of the two op-amps U5A and U5B
that amplify and buffer the forward and reflected voltages before they
go to the processor. There are two resistors on the outputs that are
very close to each other and the pads were shorted so the processor
saw the same voltage for forward and reflected - ergo SWR of 9.9-1.
And the voltage varied with the C1 setting as the bridge went in and
out of balance - ergo the varying power indication. Totally a build
error. When I folded over the resistor leads, they ended up looking
like they were on a single pad. I think if you look at that area you
will find the problem.
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