Home › Forums › Help/Technical Questions › Vintage MMD age identify from capacitors?

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  • February 23, 2009 at 6:31 pm #77792
    Bonovox400
    Participant

    Hi all. I’ve tried to find any vintage MMD circuit board or open unit pix on the web, and only find current stuff. I can throw some pics up if necessary, but I have a 5 knob unit with the red label that is supposedly from late 70 or early 80’s. At least the previous owner proported this. It does have a brown, 2 prong outlet plug, so i’m pretty sure it can’t be a reissue since it doesn’t even have a ground.
    I’m afraid to remove the knob covers and get the front of the unit off, so I took out the 6 screws in the back and removed that cover. The PCB is unlabled and appears pretty old (basing this on the way some electronics, pc’s circuit boards looked like in the early 80’s) I can’t find anything of note with dates and such, but If I tild the board slightly, i can see what looks like a large blackish colored, long capacitor maybe… and there is repeating numbers on it that shows 86* (degrees symbol) and under that the # 78 and a symbol that sorta looks like a copyright logo, but isn’t. IDK if it’s a production date mark or something relating to voltage, i’m not really sure.

    If I need to send pics, I can of the area i’m talking about. I’m just very hesitant to remove the circuit board due to the fragilness of the whole thing. :-) Thanks for any help!

    February 23, 2009 at 6:40 pm #93854
    The EH Man
    Moderator

    Pot codes are generally accepted as a reliable source for dating but I’m not sure about cap codes as they’re more likely to have been replaced.
    The unit isn’t as fragile as you think. Take it apart, check the back of the pots for the codes.
    The latest code would be your date.

    February 23, 2009 at 7:02 pm #93856
    Bonovox400
    Participant

    Is there a guide or method to removing the circuit board from the backside? Do I have to take off the knobs and is it just a simple turning of them? I don’t want to crack anything plastic, or strip off some threads or something similar. The pots are the underside of the knobs correct?

    Thanks again for the response.

    February 23, 2009 at 7:29 pm #93859
    The EH Man
    Moderator
    Quote:
    Is there a guide or method to removing the circuit board from the backside? Do I have to take off the knobs and is it just a simple turning of them? I don’t want to crack anything plastic, or strip off some threads or something similar. The pots are the underside of the knobs correct?

    Thanks again for the response.

    Remove the knobs, then remove the nut on each control shaft. Gently lift the board up and look at the back of each pot.

    Quote:
    The pots are the underside of the knobs correct?

    Correct. They’re the controls.

    February 23, 2009 at 7:38 pm #93860
    Bonovox400
    Participant

    But what is the exact method for removing the knobs? Just keep turning when they reach their 0 or “max” position? Sorry about the newbness to knowing the mechanics of effects boxes. :-P

    February 23, 2009 at 7:45 pm #93861
    The EH Man
    Moderator
    Quote:
    But what is the exact method for removing the knobs? Just keep turning when they reach their 0 or “max” position? Sorry about the newbness to knowing the mechanics of effects boxes. :-P

    Just grab and pull. If it’s a vintage unit, the knobs should come right off.

    February 24, 2009 at 11:36 pm #93910
    Bonovox400
    Participant

    I tried pulling up on the knobs. (the box is together, all screws in place fyi) and they seem to move about a centimeter up, but there is no give after that. I pulled pretty hard but it doesn’t seem like it wants to pop off, or is designed that way?? I don’t think it would require me to use a ton of force to remove and from what you say, I don’t think it’s right if it doesn’t just “come off”

    What else should I try? Do I need to remove anything special, or loosen what looks like a washer-type nut below the knob, before I do this? I tried pulling on all knobs and they don’t seem to want to just come off, so I don’t think they could all just be “stuck”. :-/

    February 25, 2009 at 1:16 am #93920
    The EH Man
    Moderator

    Do you have replacement knobs that are held on with set screws?

    February 25, 2009 at 5:49 pm #93940
    Bonovox400
    Participant

    They might be, but I don’t know what replacement vs. originals look like. They look like knobs with the points on them that i’ve seen on other pictures of this model. I’ll just attach some pics after work and you can let me know if they have screws, or i’m just paranoid and afraid to use a little elbow grease. lol.

    February 25, 2009 at 5:53 pm #93941
    The EH Man
    Moderator
    Quote:
    They might be, but I don’t know what replacement vs. originals look like. They look like knobs with the points on them that i’ve seen on other pictures of this model. I’ll just attach some pics after work and you can let me know if they have screws, or i’m just paranoid and afraid to use a little elbow grease. lol.

    If it has set screws there will be a little hole on the side opposite the pointer. The screws are in there.
    Can you post a pic of the circuit board in yours?

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