qcxHi Roland,
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By "open," I mean very large resistance between the leads, as in an open circuit.
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It would look like the drain of Q4 is not connected because the center lead is cut off.? The drain is the tab at the top of the device, as in the datasheet:
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Measure the resistance across L1, L2, L9, and L10 with the power off and disconnected.? All should be very low, almost zero ohms.? I believe that one or more of these inductors is an open circuit.? If not, we must check that the diodes switch on and off when receiving and transmitting.? Measure the voltage on the cathode (banded side) of the diodes.? It should be high when receiving and low when transmitting.? Run this test with the QCX in practice mode or the QCX output connected to a dummy load and the input to the amp connected to a separate dummy load.? In total, not using the practice mod requires three dummy loads.? One is for the QCX output, another is for the amp input, and the third is a high-power dummy load for the amp output.
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Note:? All transmitter tests should be done with an adequately rated dummy load connected to the RF output, even when no RF is expected.? Also, any input should be terminated in a 50ohm load, either the source transceiver or a dummy load.
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73
Evan
AC9TU
