Home › Forums › Help/Technical Questions › DMM 90’s delay knob issue

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  • April 10, 2011 at 9:44 pm #81536
    esharp
    Member

    Mid 90’s DMM. Type with relay bypass, 4 MN3008. The delay time adjust was beginning to come and go more than halfway up. Now I’m getting no delay if adjusted more than about halfway. Any ideas on what’s gone bad?

    Tim

    April 10, 2011 at 9:48 pm #114958
    The EH Man
    Moderator

    I’m going to guess that the pot may be cracked on the carbon track. If it is, it’ll need to be replaced.

    April 10, 2011 at 9:56 pm #114959
    esharp
    Member

    So I should be able to put a meter across it and see if that’s the case right?

    April 10, 2011 at 9:59 pm #114960
    The EH Man
    Moderator
    Quote:
    So I should be able to put a meter across it and see if that’s the case right?

    Yes, but you’ll need to disconnect the pot for an accurate reading.

    April 10, 2011 at 10:07 pm #114961
    esharp
    Member

    Smooth as silk from 0-100k. Next?

    April 10, 2011 at 10:13 pm #114962
    The EH Man
    Moderator

    Solder joints on the pot?

    April 10, 2011 at 10:14 pm #114963
    The EH Man
    Moderator

    As long as you have it out, you might patch in another 100k pot and see if the problem persists.

    April 11, 2011 at 2:17 am #114964
    esharp
    Member

    Don’t think solder joints as that would be more all or nothing. Everything looks good. Was able to test pot without removing. Is the amount of delay a simple voltage controlled input to the MN3008s of which the pot is one side of a voltage divider is it more sophisticated than that? Guess I should try to find a schematic.

    April 11, 2011 at 2:26 am #114965
    The EH Man
    Moderator

    It’s more sophisticated than that.

    April 11, 2011 at 10:16 pm #114977
    The EH Man
    Moderator

    You might also check that the wiper is making contact with the track all the way around. Check resistance from center to one end than turn the knob/shaft while measuring.

    April 19, 2011 at 5:11 pm #115052
    Howard Davis
    Member

    I designed it, so I certainly can fix, and if you want, custom-mod it.

    Howard Davis, EE
    Guitar pedal design engineering, repairs, and custom mods:
    http://howardmickdavis.com
    Direct email: howard.davis2@att.net

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