[Elecraft] KPA100 troubleshooting

[Leo Starrenburg PA5LS]

LS

I had a closer look at U5a/b and U6 this evening. It seems I misinterpreted
the voltage on the VRFDET line, which led me to believe there was a fault of
sorts in the scaling.

The output of U6 is wrong ie: with 1.5 V at the positive input, the output
generates only 0.36 V, which gives 0.18 V at the negative input. Assuming
that the load of U6 is the same as the
KAT2 (which works), and having checked the line from U6 pin 6 to the end of
the flatcable, U6 must be defective.

I could try another op-amp to source the VRFDET line, apart from the enable
line or maybe the rail-to-rail capability of the EC5146C, I can't see a good
reason why a 100MHz op-amp is used here. (Which probably shows my ignorance
in this matter :))

73' Leo.