GGG P-90 troubleshooting help

[timmyhiggy]

Hi all,

I have been building a P-90 (all details here http://www.generalguitargadgets.com/projects/23/311-mxr-phase-90-script-logo) but have a problem in that it doesn't seem to phase at all.
I have been communicating with JD from GGG and he says I need to have a check of some of the componants, however, I went over it all with a soldering iron to check I hadn't got a cold solder joint anywhere and it hasn't changed.
Currently, when I connect it up with guitar, amp and power supply, it bypasses properly, and then when I turn it on the LED comes on but it doesn't sound any different (it does sound a tiny bit squeezed, but not a very noticeable change)

These are my multimeter readings:
Pin.  1   2        3        4   5     6        7      8
Ic1   0   4.25   2.85  0    0    4.25   8.9   0
Ic2   0   4.27   4.26  0    0    4.29   8.9   0
Ic3   0   4.27   4.26  0    0    4.25   8.9   0
Ic4   0   4.27   4.26  0    0    4.29   8.9   0
Ic5   0   4.27   4.26  0    0    4.25   8.9   0
Ic6   0   ~4.4   ~3.7 0    0    ~4.4   8.9   0

~ means varying with time. I had the pot turned as far anti clockwise as possible when taking these readings.

Q1--4 are d: 4.27 s:4.27 g: 1.43
Q5 is c:2.49 b:3.67 e:4.27

They are all constant and not time-varying as I guess a phase pedal should be.
Could someone suggest where to start, because at this point I'm a little overwhelmed when it comes to what to do next!

[Govmnt_Lacky]

Welcome Timmy!

What kind of FETs did you use for Q1-4? Also, what zener did you use for D2?

Could you post up some pictures of your build? You will need to use a file sharing program (dropbox, photobucket, etc.)

[timmyhiggy]

Cheers for answering my distress call!

The Q1-4 are the 2N5952 that came with the kit, as is the F231B D2. I'll do some pics in a bit...

[dwmorrin]

I have been communicating with JD from GGG and he says I need to have a check of some of the components, however, I went over it all with a soldering iron to check I hadn't got a cold solder joint anywhere and it hasn't changed.

When checking components, a multimeter is a much more useful tool than a soldering iron.  Use the meter's low resistance/beeper setting to verify connections... then bust out the iron when you find a bad connection.  Not that is was a bad idea for you to resolder everything - just more work than you have to do... and rarely does shotgun soldering fix a problem.

Ic6   0   ~4.4   ~3.7 0    0    ~4.4   8.9   0

~ means varying with time. I had the pot turned as far anti clockwise as possible when taking these readings.

Q1--4 are d: 4.27 s:4.27 g: 1.43

IC6 is your low frequency oscillator, so varying readings there is a good sign.
The gates of Q1-4 receive the output of IC6's oscillations.  If the gates aren't wiggling, then that's where I would look.
FETs can be tricky.  They have to get biased by that 250k trimmer.  Does the trimmer have no effect?

[timmyhiggy]

The pot didn't seem to have an effect, no.

As for using the multimeter to find a bad connection, can you explain how to do that in a moron-proof way? I'm a bit of a noob when it comes to this!

EDIT just read a guide, it seems like on my multimeter I have to just check there is 0 resistance between the leg of a componant and the leg of the componant on the other end of the trace?

here is an image of the board
https://drive.google.com/file/d/0BxZnrZ4X2mVleGpkQlNTbXRydm8/edit?usp=sharing

[dwmorrin]

The pot didn't seem to have an effect, no.

As for using the multimeter to find a bad connection, can you explain how to do that in a moron-proof way? I'm a bit of a noob when it comes to this!

EDIT just read a guide, it seems like on my multimeter I have to just check there is 0 resistance between the leg of a componant and the leg of the componant on the other end of the trace?

here is an image of the board
https://drive.google.com/file/d/0BxZnrZ4X2mVleGpkQlNTbXRydm8/edit?usp=sharing

Yes, put your multimeter on the lowest ohms (Ω) setting and check for a near 0 reading.  Sometimes the solder side will look connected, but the leg is short or something, so probing the component side is somewhat more "moron-proof", especially for socketed IC connections.
Most multimeter will have a "beeper" or "buzzer" setting so you don't have to keep looking at the screen.  You just listen for a buzz/beep when the meter reads <50Ω (actual threshold may vary).  Sometimes the diode setting doubles as the beeper.

Does the trimmer affect the voltage at the Q1-4 gates?  Explicit instructions, if needed: Take gate measurements at trimmer full CCW, middle, and CW.  Does the gate voltage change?  If it does not, check the connections from trimmer wiper, to R17, to gates.

If it does, then your oscillator may not be reaching the gates.  Check R18.

Couldn't open that file.  You should set it to public, or post it outside of your google drive account.

[timmyhiggy]

The pot didn't seem to have an effect, no.

As for using the multimeter to find a bad connection, can you explain how to do that in a moron-proof way? I'm a bit of a noob when it comes to this!

EDIT just read a guide, it seems like on my multimeter I have to just check there is 0 resistance between the leg of a componant and the leg of the componant on the other end of the trace?

here is an image of the board
https://drive.google.com/file/d/0BxZnrZ4X2mVleGpkQlNTbXRydm8/edit?usp=sharing

Yes, put your multimeter on the lowest ohms (Ω) setting and check for a near 0 reading.  Sometimes the solder side will look connected, but the leg is short or something, so probing the component side is somewhat more "moron-proof", especially for socketed IC connections.
Most multimeter will have a "beeper" or "buzzer" setting so you don't have to keep looking at the screen.  You just listen for a buzz/beep when the meter reads <50Ω (actual threshold may vary).  Sometimes the diode setting doubles as the beeper.

Does the trimmer affect the voltage at the Q1-4 gates?  Explicit instructions, if needed: Take gate measurements at trimmer full CCW, middle, and CW.  Does the gate voltage change?  If it does not, check the connections from trimmer wiper, to R17, to gates.

If it does, then your oscillator may not be reaching the gates.  Check R18.

Couldn't open that file.  You should set it to public, or post it outside of your google drive account.

Thanks for the clarity.
I shall go through all the componants doing a continuity check. With regards to the trimmer adjustments, you mean the little thing that looks like you could get a small flathead screwdriver into it?

[dwmorrin]

With regards to the trimmer adjustments, you mean the little thing that looks like you could get a small flathead screwdriver into it?

Yep.  That's the trimmer.  And yes, you'll need to take a small flathead screwdriver to it.  If you haven't adjusted it yet, then you may find that this is your problem.  Monitor the output while adjusting to check if the pedal starts working.

[timmyhiggy]

cheers for the helpl everyone, turns out that it just needed the trimmer adjusting into the sweet spot! Getting some lush early EVH-style phase sounds out of it now