Phase 90 not phasing - HELP!

[nobodysweasel]

I'm going crazy over a phase 90 that I just built, and I need some help.  I followed the GGG project found here: http://www.generalguitargadgets.com/projects/23-phase-shifters/311-mxr-phase-90-script-logo.  I did not have a 15uF cap, so C7 is a 10uF and 4.7uF in parallel.  For my JFETs I used 2n5485 which I matched using the geofex circuit.  Three of them measured 0.72 V and the other measured 0.71 V.  I also tried another set that were 0.79, 0.80, 0.80, and 0.81 with the same results.  I used TL071's for all of my IC's.  I'm getting a guitar signal through it, but it's not phasing.  I've checked over and over for solder bridges (visually and with multimeter) or wrong parts, but everything looks okay.  I've quadruple checked the jfet pinouts (which are backwards from the jfets in the schematic).  Here are the voltages I measured:

Q1-Q4  G   4.5-4.8 V
           S   5.00 V
           D   5.00 V

Q5       C   3.85 V
           B   4.44 V
           E   5.00 V

IC1      1   0.14 V
           2   5.00 V
           3   4.77 V
           4   0.00 V
           5   0.14 V
           6   5.00 V
           7   9.53 V
           8   0.00 V

IC2-5   1   0.14 V
           2   5.00 V
           3   5.00 V
           4   0.00 V
           5   0.14 V
           6   5.00 V
           7   9.52 V
           8   0.00 V

IC6      1   0.27 V
           2   2.01 V
           3   5.81 V
           4   0.00 V
           5   0.15 V
           6   8.52 V
           7   9.52 V
           8   0.00 V

The above measurements are with the trim pot all the way up.  With it all the way down, a few values change.  The JFET gates oscillate from 0.74 - 1.06 V.  IC6 starts to behave really strangely.  Pin 1 varies from 0.00-0.27 V, pin 2 from 4.24-5.86 V, pin 3 from 4.03-5.91 V, pin 5 from 0.00-0.15 V, pin 6 from 1.30-8.91 V.  These oscillate regularly except for pins 3 and 6 which periodically jump from the minimum value to the maximum value and back again.

There are some numbers here that are clearly off, but I can't figure out what's going wrong.  Pin 2 of IC1 and pin 6 of IC2-5 make me think maybe there's a solder bridge somewhere.  I can't find one.  There are also several values that should be less than 0.01 V, but mine are all 0.14 V.  I don't know if this is a big issue or not.  There are a handful of other values that are off.  And then there's IC6 going crazy  .  It also seems a little strange to me that so many of these numbers are off, yet I'm still getting a guitar signal through it, just no phasing.  I would expect it to be completely dead.

Any help at all would be much appreciated here.  I'll try to see if I can get some pictures uploaded later, if anyone thinks that will help.

[PRR]

> IC6 going crazy

It is *supposed* to bop around like that. That's what makes the FETs wobble.

Question is: howcome IC6 is wobbling but the FET gates are not?

[nobodysweasel]

Well that's good to know that IC6 is supposed to wobble like that.  The voltages at GGG didn't say anything about that.  And the gates of the JFET's are also wobbling.  Depending on where I have the trimpot the values change (as I believe they're supposed to).  At one extreme it's 4.5-4.8 V, and at the other it's 0.74-1.06 V.

[JRB]

Might not be much help but I have been trying to get the same circuit working for like half a year now using the data from ggg, and I have the exact same problem as you. Working LFO, brand new matched JFETs but no phasing. Even the voltages match up in roughly the same way.

Do you happen to have a oscilloscope? if you do could you check what the signal looks like at pin 6 of IC2,3,4 and 5.

[Vince_b]

I won't help you either, but I had the same problem with a Phase 90 built with the GGG layout. Amongst the 30 or more pedals that I built, this is the only one that I could't get to work after the usual debugging.

Edit: Actually it was the tonepad layout.

[jimilee]

I know usually it's the jfets that's the problem typically in a situation like this, I built a bear phase 45 and the pin outs were actually reversed depending on which jfets you used. Just a thought

[armdnrdy]

Have you tried any other zener diode value beside the 5.1 volt listed in the schematic?

If you haven't, try a 4.7 volt, check for phasing and then try a 5.6 volt.

It's best to socket the zener with a few single in line socket pins until you find the correct zener, then remove the pins and permanently solder the zener.

[nobodysweasel]

Do you happen to have a oscilloscope? if you do could you check what the signal looks like at pin 6 of IC2,3,4 and 5.

I don't have an oscilloscope.  This is the first time I've encountered a problem where I really wish I did  .

Have you tried any other zener diode value beside the 5.1 volt listed in the schematic?

The only zeners I have are 5.1 volt, and I didn't have the forsight to socket it either.  I'll see if the electronics shop in town has them and give swap them out before I give up on it and maybe try to find a different layout.  It sounds like several people are having the same issues with the GGG project.

Seriously, thank you everyone for the responses.  I'll work at finding a solution, and if I do I'll make sure to post it.

[JRB]

Another question for you did you buy their pcb or just followed the layout/schematic they posted? Cause I noticed there is a path on the pictures of the pcb going from IC5 to the mixing resistors that's on the backside of the board maybe its that path that's missing on your board.

[nobodysweasel]

Another question for you did you buy their pcb or just followed the layout/schematic they posted? Cause I noticed there is a path on the pictures of the pcb going from IC5 to the mixing resistors that's on the backside of the board maybe its that path that's missing on your board.

I etched my own board and I had NO idea there might be traces on the other side of the board!  I didn't see anything in the project files, but now that I look at the photos there is definitely a trace there.  I'll add some jumpers tonight and see how it goes.  Thanks for the tip!

[armdnrdy]

JRB is correct.

The GGG layout isn't showing a jumper that should be installed on the self etch version of the PCB.

On the "real" script 90 there's a 150K resistor that's jumped between pin 6 of IC5 and the 150K resistor that connect to Q5.

GGG put this resistor on the board. (R24)

So you need a jumper between R24 (the opposite side of where it connects to R26 and R27) and the solder pad between R14 and pin 6 of IC 5.

[nobodysweasel]

JRB and armdnrdy got it right.  I followed the trace on the image of the PCB on GGG, which required 2 jumpers and 1 resistor I was missing (R15 isn't marked in the wiring diagram image, even though there are pads for it).  As soon as I got those in there it started phasing like a champ!

Forgive me this one indulgence:  I'm going to summarize the problem and solution one more time so that it will be more likely to show up using the search function for others who have this problem in the future.  The layout for the Phase 90 Phaser from General Guitar Gadgets (GGG) requires jumpers to be used that aren't explicitly explained in the project files.  If you purchased a board from them, this is not an issue.  If you etched one yourself, look at the images of the PCB on their site to see where they need to go.  If your Phase 90 is not phasing and you etched your own board, this is likely the problem.

Thanks again to everyone for your help.  I don't know what I'd do without you guys!

[JRB]

No problem glad to be able to help.