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Hi Evan,

thanks for your help again.

The next thing to test is the pins 10, 11, 12, and 13 of IC402.? The selected filter should be 2.5 volts, and the others should be close to zero.

I get the following:

That looks fine to me. Or am I mistaken?

If the above checks, test that Q508 is turned on while receiving.? The source and drain should be close to zero volts.

Not so sure on this one: Drain 0.64V, Source 0.07V, Gate 0.69V - no matter what band I select. - Is this maybe the suspect? Strange, as there was no re-soldering in that vicinity.

The last check would be testing the low-pass filter diodes and toroid connections.? Only the two for the selected band filter should be one of the six diodes, measuring close to zero volts on the banded (cathode) side of the diodes.? The other diodes should be close to the input voltage to the QMX.? Both toroids in the LPF connection are required to get the diode to switch on.

This looks also good to me:

80m: D508 & 511 0V
60m & 40m: D509 & 512 0V
30m & 20m: D510 & 513 0V

I am discounting the quadrature sector and T401 based on the discrimination of the sideband, though at a low level.? That would not happen if there were an issue with the I/Q processing through the audio codec.

OK.

Others in the group may have different ideas and may be better at isolating the problem.

... yes please. Any ideas welcome :).

But my interpretation would be a fried Q508 ... so change one BSS123 MOSFET.

Please confirm this diagnosis.

Thanks again and Vy73

Stefan.

--

Stefan U. Hegner    <db4st@...>
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