Home › Forums › Vintage EHX › Old Polychorus: chorus and doubler modes not working

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  • July 9, 2019 at 5:16 pm #85647
    LuckyPierre
    Member

    I’m trying to fix an older polychorus big box with mn3009 and mn3008 chips. I’ve tested the switch with a meter and it is working. I need to trace the path of these positions to determine where the issue is occurring.
    Does anyone have a link to a schematic or have any suggestions what may be causing this issue?
    Flanger and filter matrix modes are fully functional.
    https://images.equipboard.com/uploads/item/image/20510/electro-harmonix-vintage-polychorus-xl.jpg?v=1557945536

    July 9, 2019 at 8:58 pm #125380
    The EH Man
    Moderator

    The MN3008 works only for the Chorus and Doubler. Input is at pin 7, output at pins 3 and 4. Might be bad, might need rebiased (Bias trim is connected at pin 8). Clock signals at 2 and 6 but the clock’s probably OK since the Flanger is working.

    July 9, 2019 at 9:52 pm #125375
    LuckyPierre
    Member

    Cool thanks for the info, I’ll check that out!

    July 21, 2019 at 3:29 pm #125401
    Frandid
    Member

    This is not the old Polychorus, this is a 1990 reissue ! They don’t look the same, they don’t sound the same, not the same IC’s. Yours is much closer to the present Polychorus in a different housing, inspired from the original but not the same. In my opinion the original sounds better in chorus mode, I own one since 1979.

    August 1, 2019 at 3:49 am #125418
    LuckyPierre
    Member

    I got a repro mn3005 to swap with the mn3008 to see if the chip was failing. When I started tinkering with the trim pot the chorus and doubler made came on and off intermittently when I tapped on the trim pot with the screwdriver.
    I put the original mn3008 back in and same thing happened. So I know the chip works now. Tomorrow I will try reflowing the trim joints.
    While poking around the green wire coming from the second output came loose.
    Anybody know where that wire is supposed to go?

    August 2, 2019 at 7:51 pm #125426
    LuckyPierre
    Member

    So I replaced a bunch of flimsy wires. The effect works if i tap the trim pot with a metal tool. Then as soon as I touch the feedback knob or touch any of the pots to the enclosure it kills the effect again. I guess my next move is to replace the trim pot.

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