Re: CQX+ 5W very low audible tone

Roelof Bakker

Hello Mateo,

I had a similar issue with my QCX for 80 meter.

The voltages on IC10 pin 1, 2, 3 and 7 is too high.
It should be about 5.6 V.

In my case this voltage drifted up over time until it reached 10,4 V and the amplifier shut off.
The culpritt appeared to be a likely leaky C22, 1 uF, capacitor. I replaced this capacitor and
everything was fine.

The stage after the gain potentiometer is an inverting amplifier, so when the input gets low the output
will get high. In your case there might be a slight leakage to ground. Not enough to clamp the output to
full Vcc.

I had measured this capacitor before mounting it and it shows nothing special on a capacitance meter.

I hope this helps.

It took me quite some time to figure it out.

Roelof, pa0rdt

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