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Makes me wonder if there isn't a switching problem here. The two slug-tuned trimmer coils are kept out of the crystal circuit in USB mode with switching diodes. If the control voltage for those diodes is wrong, one of them could be active in USB mode when it shouldn't be. In USB the only one of those three adjustments that should respond when turned is CT3. If spinning the slug of either L19 or L20 causes the PLL frequency to change, that's the problem. A shorted switching diode D32 or D34 could have happened if someone dropped his screwdriver onto the solder side of the board while energized. Likewise, switching voltage that activates either D32 or D34 should NOT be present in USB mode.

Shoulda thought of this earlier.

73

[QUOTE="nomadradio, post: 849699, member: 22"] Makes me wonder if there isn't a switching problem here. The two slug-tuned trimmer coils are kept out of the crystal circuit in USB mode with switching diodes. If the control voltage for those diodes is wrong, one of them could be active in USB mode when it shouldn't be. In USB the only one of those three adjustments that should respond when turned is CT3. If spinning the slug of either L19 or L20 causes the PLL frequency to change, that's the problem. A shorted switching diode D32 or D34 could have happened if someone dropped his screwdriver onto the solder side of the board while energized. Likewise, switching voltage that activates either D32 or D34 should NOT be present in USB mode. Shoulda thought of this earlier. 73 [/QUOTE]

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