1975 Script logo phase 90 not phasing very well

Discussion in 'Effects, Pedals, Strings & Things' started by jasonvilla, Apr 24, 2015.

  1. jasonvilla

    jasonvilla Member

    Messages:
    7
    Joined:
    Dec 21, 2012
    Hi all. I recently cleaned up and installed a true bypass on my '75 phase 90. I cleaned out 40 years of melted foam in the process. Well something I did pissed it off because it isn't phasing very well anymore. Everything works fine except the depth of the phase doesn't seem to match what it used to. And when its on the slowest setting I can't even hear a difference in tone. Highest speed seems to at least tremolo with minimal phase shifting. The volume is the same with the effect on or off. Theres 9.5v going into it. The diode is working fine. I checked c15 to see if it was open and its fine. The bias trimpot has 5v going into it and 2.5v going out which seems good. I checked all of the voltages that are listed on the http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-90-script-logo/ instructions. Most everything looked about normal except:
    Pin 6 on IC2-IC5 is 5v on my unit and apparently it should be 2.1v.
    Pin 6 on IC6 goes from 1.8v to 8v on mine. Instructions says 4v. Not sure if this is normal.
    The only other thing is the collector on Q5 is 3.2v on mine and instructions says 4.3v.
    Sorry for the long post but I wanted to try and cover everything I could. I really appreciate any help!! Thank you!
     
  2. tedm

    tedm Gold Supporting Member

    Messages:
    6,901
    Joined:
    Dec 29, 2002
    Location:
    The OC
    I have a block logo one with the barrel 1/8" power adapter and had the effect go out, even with a new battery, turns out it was just a touch of the trimpot with a jewellers screwriver to get it back like new. You definitely need to be playing it while setting it.
     
  3. TheoDog

    TheoDog Silver Supporting Member

    Messages:
    18,468
    Joined:
    Jan 17, 2011
    Location:
    Bethany, OK
    It would be worth sweeping the trim pot just to see if it gets the effect right.
    Sound like you know enough to be able to do and undo any changes.
     
  4. jdel77

    jdel77 Silver Supporting Member

    Messages:
    8,289
    Joined:
    May 25, 2009
    Location:
    Melbourne, 'Straya...maaate...
    Yep. Just move the trim a touch til it's in the sweet spot. It won't damage anything.
    If its still not happening then maybe Q5 may need replacing.
     
  5. jasonvilla

    jasonvilla Member

    Messages:
    7
    Joined:
    Dec 21, 2012
    I've tried adjusting the trimpot. It tremolos the most where it was in the stock soldered position. I don't think thats it. So you think Q5 is toast?
     
  6. Icedstevo

    Icedstevo Member

    Messages:
    726
    Joined:
    Mar 10, 2015
    I had to remove crumbly foam from an old phase 90 as well. Its a long shot but maybe the board is shorting out somewhere to the metal box. I used cardboard paper cut to size to stop this from happening.
    Sorry that's all I've got:dunno
     
  7. jasonvilla

    jasonvilla Member

    Messages:
    7
    Joined:
    Dec 21, 2012
    Thats not it, but thank you for the suggestion. :)
     

Share This Page