GGG Phase 90 Problem

[armdnrdy]

Something is keeping the gates "pegged" at reference voltage instead of oscillating.

The bias trimmer via R17 has no effect on the gate voltage nor does the LFO through R18.

I would look very closely for a solder bridge between either the source or drain and one of the gates. The source and drain should be at reference voltage which they receive unaffected by the trimmer, so this would be a logical explanation why the gate is measuring ref voltage as well.

Edit:
Also look for a bridge around R4, R5, & R6. All three resistors cross the trace that connects the four gates.

[Jeeper2000]

Because I'm borderline obsessive about getting this thing to work, I took a picture of the back of the PCB on my phone so I could study it at my desk at work next to the layout.  I found an enormous solder bridge in the picture connecting the source and gate next to Q4.  It is so perfectly perpendicular to the gate trace, my eyes must have been seeing it as part of the trace.  My embarassment of not catching it sooner is outweighed by the excitement that I may be phasing by sundown.  I'll post a followup after I get that mess cleaned up.

[armdnrdy]

Good to hear!

That should take care of the problem!

I'm glad because I was running out of things to check!

Definitely update when you get it fired up.

You won't know until you adjust the bias but you may have to change the zener back to the 5.1.

[Jeeper2000]

Desoldered the bridge and we now have oscillation at the gates!  I'll have to try it with my guitar when I get home.

[armdnrdy]

Desoldered the bridge and we now have oscillation at the gates!  I'll have to try it with my guitar when I get home.

[Jeeper2000]

We are phasing! Thanks to armdnrdy for sticking with me on this thread to get this thing working right. This is my 8th pedal build and the first solder bridge I've managed to miss completely. The 5.6 Zener is working great and giving me readings very similar to the GGG instructions, so I'm gonna leave it be. You guys are great. Thanks again for all the help. On to the next project!

[armdnrdy]

I was wondering what happened to you and the update 

I had the vision of you plugging in the phaser and playing guitar for three days and three nights straight, getting fed your dinner from your wife/girlfriend, (while you kept playing) skipping work, missing a doctor's appointment, and blowing off a court date just because it sounded so damned good! 

[Jeeper2000]

Ha! I wish! I have a sister in law that had back to back college graduation events the past two nights. Made it tough to find time to rock out. Add our 4 month old to the equation and its even more complicated. Loving the phase though. My buddy had a vintage Script 90 that disappeared at some point. I told I built my own and he's way jealous. I might wind up building a second one