I have a Dr Q and apparently the IC is stuffed

1) how do you test one?
2) is there a replacement? - looking at the archives it seems like it's easier to do another build

Thanks

Stock Dr Q needs a 1458 for suitable sweep.  Other dual-ops deliver either little sweep or something that is too wide to be of use.  Jack Orman's mods that result in the Dr Quack and Nurse Quacky remedy this.

How do you know its a bad chip?  Partly by reading voltages on the relevant pins once you have confiurmed there are no solder bridges, cracks in traces, etc, and that all parts are installed and oriented where and how they ought to be.  You should get a couple of volts out of the envelope follower when you strum.

Thanks!

If any one knows what voltages should be coming out of where that would be nice.

With the guitar plugged in, measure the AC voltage coming out from the wiper of the sensitivity control at different settings (should be somewhere in the range of 50mv or so depending how you pick and whether there are any pedals before the NQ), from the output of the envelope follower (output pin of of op-amp, should be at least a couple of volts), at the junction of the LED and 51R resistor (should be at least a couple of hundred millivolts) and at the gate of the transistor (at least 50mv and probably more like a few hundred mv).

The LED connected to the + input of the envelope follower should be on all the time, and the other LED should flash briefly when you play.  If both those events occur, then there is a good chance the transistor is misoriented (i.e., a pin misunderstanding).  Those are the most common sorts of problems besides insufficient signal to drive the pedal (which would have symptoms of one LED always on and the other never or barely flashing)

Slightly OT:

Has anyone tried a 1458 in a Dr. Quack/Nurse Quacky? I'm wondering if it's still not the best OA for the circuit even with the LEDs.

RDV

The 1458 is used in the Dr Q because of the amount of voltage swing it provides, given the supply and input (and I suppose the output impedance, current delivery capabilities, etc.).  I tried a bunch of different dual op-amps (the usual culprits and some unusual ones too) in a stock Dr. Q circuit, they either refused to sweep, or else swept so wide you couldn't even *hear* a wah in there.  The 1458 swept in a a musically useful and pleasing manner, even if the noise level and other tonal aspects were not the best.  The Orman mod is intended to permit chips with better sonic charanteristics to sweep in a usable fashion in that particular circuit.  With the mods, I can't see the 1458 outperforming any of the alternatives.