MN3007 bias problem in DOD FX75C flanger?

[qubuntu]

Hi there, this is my first post, but I've been lurking for ages I'm quite new to all this, so I appreciate this might be a stupid question...!

I've recently acquired a DOD FX75C (same as FX747 apparently) which is faulty - when you turn up the feedback level, it really starts distorting. I've been all through the circuit with an audio probe and right up to the input of the MN3007 it's clean - straight afterwards it's very distorted. I'm a bit lost for ideas. Is this due to normal clock noise on top of the signal which the filter is then failing to remove, or might it be a biasing issue for the BBD input perhaps?

Circuit is running at a healthy regulated 9V btw.

Many thanks in advance

[armdnrdy]

Well...with no trimmers to adjust the bias...I would check the bias voltage to make sure that you have 4.5 volts.

Also, I would check/replace resistors/caps in the feedback path since that's where you are having the issue.

Maybe DC is making it's way into the signal path???

[Fender3D]

Watch out:
BBD's bias is NOT the same as "audio" bias label, on schematic, indeed it's set by R48 and R49.
Actually slightly more positive than half Vcc.

You'd better check BBD's output signal after Q7 it's cleaner there...

[qubuntu]

Thanks guys

Voltage at input of MN3007 varies between 4.63V and 4.85V through the clock cycle.

Audio at emitter of Q7 is no cleaner sounding than at the audio output of the MN3007.