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Yes, I've tried a variety including a MXR ISO-Block.

Everything squeals starting from the first component. I really don't want to chuck this in the bin, but am I out of options here?

One thing I noticed is that there are no electrolytic capacitors (or any for that matter) from C19-C21. Only C22. Just confirming the others mentioned apply to the 2015 model. I have them on order now.

In fact, there is squeal everywhere in the circuit. I started by replacing C1 assuming that's where the squeal began, and then was confronted with the same squeal. I am actively looking into this. Thanks for the heads up.

Part was replaced, no discernible change, sadly.

Part is ordered and we'll find out Thursday. Thanks.

I previously had checked the LM7815 and the values I was reading were consistent with the documentation and advice provided in this thread. I want to make sure it's still a good idea to swap it out or if there was something else I should be looking for.

It's in the 2015 subfolder in the zip archive:

https://www.madbeanpedals.com/projects/archives/FilterMod/HarbingerOne.zip

Scruffie - I've swapped C32, C33, and C34 but to no avail. Is it worth going down the line and replacing the rest of the capacitors if these check out ok?

Stomptown: unless I'm mistaken - there was no filter portion for the Harbinger 2015 model.
Scruffie: I just wanted to clarify with you - it sounds like I have some work ahead of me, but I'll push through and get back to the thread. But - I wanted to state that I used the Total Recall power supply on it - which *was* AC (I think), so is it really a lost cause if that was the case??

edit: The unit is the HarbingerOne_2015 model; the D6 diode is not present since I am running at 18v.

Appreciate the tip, but the transistors all check out. The bulb seems to be working just fine and the device does make the classic univibe sound. It's just the squeal/hum that's overlaid onto it. Any recommendations as to what I might want to look for next?

Pro move - I should have known better, but I mixed up my Memory Man power supply (24 AC/AC I believe) and my Harbinger One (18v DC), and now, I have a problem with the Harbinger 'warbling' with squeal/hum at the rate of the speed knob. I replaced D1 but to no avail.

Any suggestions where I should be looking to diagnose this would be greatly appreciated.

Looking at the schematic again, I would hazard a first guess at the pair of resistors R11 and R12. They seem to map fairly well to both schematics as far as location in the circuit and value.

  Sadly, no. The pedal bug had taken over and I found myself moving on to other pedal builds. Still hoping I can stumble across a solution (or perhaps return to my analysis and figure it out for myself).