IC756PRO Rx and Tx audio level changes during warm up

Discussion in 'Radio Circuits, Repair & Performance' started by AA4PB, Jul 21, 2019.

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  1. AA4PB

    AA4PB Ham Member QRZ Page

    Has anyone noticed the gain on the fixed audio output and Tx modulator input (ACC1 connector) creeps up as the IC-756PRO warms up? With WSJT-x I notice that when Rx and power output levels are low and gradually creep up for about 20 minutes as the radio warms up. Once warmed up it stabilizes and remains stable even during Rx/Tx cycles. I've turned the radio off and let it cool while the computer and RigExpert TI-8 continue to run. Turn the radio back on and it goes through the warm up period again, indicating that the issue is the radio rather than the interface or the computer. Everything else on the radio seems to work normal at all times.

    I don't know if this is something it has always done or not. I've only noticed it since using WSJT-x digital modes because all the adjustments are left set as they were last time I used it. It's no big deal to adjust it, I'm just curious if anyone else is seeing this issue. I'm wondering if a reference voltage or something on a A/D converter is drifting with temperature.

    Thanks for any input.
  2. G3YRO

    G3YRO Ham Member QRZ Page

    The gain of ANY transistor varies with temperature . . .

    Just how much this affects the signal level of any stage depends on the circuitry of the rig.

    Roger G3YRO

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