Electronics and Music Maker Party Light

Discussion in 'The Projects Forum' started by sprite_guy, Dec 29, 2007.

  1. sprite_guy

    Thread Starter New Member

    Aug 14, 2007
    4
    0
    I have been given a sound to light unit which does not work. The pcb is marked up as E&MM Partylight.
    Now if memory serves me correctly E&MM was produced by Maplin Electronics in the UK in the early 1980's. I know its a very long shot but would anyone have a schematic I could have a view of so that I could fix the thing.

    Thanks
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Can you take a picture of the unit and post it here?

    It might be helpful to have an image.

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Color organs were pretty popular in the 1970's.

    Some of them were poorly designed; they didn't have transformers but ran directly from line power.

    If yours doesn't have a transformer, I'd recommend throwing it away and starting over, because you could kill yourself while trying to fix it.
     
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    If you carefully disassemble it make notes while you do it of how it goes together. I recommend lableling small envelopes or other containers for the different types of screws and such so you know where they go.

    Then when it's apart you start making a schematic of the unit, part values can be blank though if the reference designator is not marked on the board you will want to draw a picture of the board or take a picture and make up your own designations on that.

    I hand draw on paper but you can use a computer if that is easier. Once you have the schematic you can then go and fill in the part's values on the schematic and a parts list. Bizarre parts, ones you cannot find information on will slow you down but with a good schematic you may be able to figure out what it does or others can help.

    Once you have that you can start working on fixing it.

    Or you can take a stab in the dark and check the fuse. ;)
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    mrmeval has recommended a very reasonable course of action. If you choose to disassemble the unit, I would suggest that you use a digital camera to document the disassembly by taking pictures as each stage of the process. The pictorial record will help resolve those questions that are bound to arise when the time comes to reassemble the unit.

    hgmjr
     
  6. sprite_guy

    Thread Starter New Member

    Aug 14, 2007
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    0
    I considered dismantling it originally to copy the print layout but decided against it. I know what you mean about the unit being non isolated. Basically it rectifies the incoming mains but does not smooth it enabling thyristors to do the switching rather than triacs. The actual control circuitry relies on a microphone to pick up the sound which is fed to an op-amp to amplify the signal which is then fed to the filters (more op-amps) and finally to and gates to 'square off' the pulses. The stupid thing about it is that the microphone is live to about half the mains. Rather stupidly I didn't check this when I reinstalled the unit in an earthed metal case which resulted in a blown fuse and a shorted diode in the bridge. You would think that after 30 years repairing tv's etc I would have known better.

    Anyway thanks for the suggestions, the scrap it one looking favourite at the moment as there is a rather nice design available on the web which is fully isolated and capable of future expansion.

    Sprite_guy
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    The microphone being powered directly from the mains was a very poor idea indeed. Many mics require 48VDC "phantom power", but proper circuits use an isolation transformer for starters; they might use voltage doubler/tripler/quadruplers to get back up to 48VDC, but it's safe and relatively low power.

    What site did you find the design on? Have a link for us? :)
     
  8. sprite_guy

    Thread Starter New Member

    Aug 14, 2007
    4
    0
    The site concerned I came across by accident, but have not regreted finding it.
    The site is Elliot Lighting (and Sound) Projects and is at http://sound.westhost.com/

    Good site

    Sprite guy
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Thanks for the link!

    Actually - I too had found that site just a couple of days ago, and had another browser window open to this page:
    http://sound.westhost.com/project68.htm
    when I read your reply! (that project is a 300W/500W subwoofer)

    You're right, it IS a good site - actually, much better than good because he goes into a great amount of detail in how he arrived at his circuit configuration, and has an entertaining style of writing.
     
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