Re: qcx+ 200Hz filter gain
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Hi Mike. Since the problem corrects itself when applying 12v to pin 7 of IC7 and doesn't stay fixed, you may have a capacitor issue. C9 (47 nF) connects from pin 5 of IC7 to ground. It may be leaky. With the power off, check resistance from pin 5 of IC7 to ground. It should be a couple megohms after that capacitor charges up.
73 .. .Ron
Any suggestion please.
The QCX+ 200Hz filter has no gain. All the DC voltages and Waveforms are okay up to and including IC7 but the DC voltages on IC8 bias pins are not 2.5v ish but only 0.8v. I accidentally shorted pins 8 to pin 7 on IC7b and everything started working normally including all the voltages on IC's 8, 9 and 10. When I powered off again the fault was back but if I again shorted pin 8 to 7 on IC 7b all works normally. All values of components checked plus? around these areas. Any ideas why putting 12V to pin 7 of IC7? makes everything work normally? I don't like changing components unless I have to but have changed IC8.
Any help gratefully received.?
Thanks?
Mike G4TSQ
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Ronald Taylor