motorboating JCM800...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dix0r, Aug 8, 2004.

  1. dix0r

    dix0r Guest

    hey guys - i posted this over on harmony central the other day - i was just hoping somebody around here might be able to help me out a little more specifically, as i still don't really know what to do :[

    i've got a JCM800 2204 thats motorboating. i've discharged the caps and checked everything with a DMM. none of the caps appear visually to be leaking or exploded or anything, and thats what i keep hearing to look for.

    according to the tom mitchell book, you can test the caps by hooking up a 9V battery to them, checking the voltage, disconnecting the battery, and seeing how long they hold their charge. i'm not really sure how long they should though, so i don't know if they're functioning properly or not. also, i think i'm going to have to remove the circuit board to test some of the remaining caps.

    according to another site i found, motorboating is almost always a signal that the decoupling capacitors in the B+ lines of the preamp section need replacing. then, a tech on HC told me that is unlikely because they aren't electrolytic. so, i would just like to know which ones to examine, or start off replacing. or if i should just check them all. if anybody could help me out i'd really appreciate it.

    thanks very much...

    -mike
     
  2. JamesPeters

    JamesPeters Member

    Messages:
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    Joined:
    Jul 3, 2002
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    Winnipeg
    The guys on HC are right. Either replace the caps, and/or buy that tester, or take it to a tech. There are no other options. Nothing realistic anyway.
     
  3. dix0r

    dix0r Guest

    just wanted to say though...

    i actually sprayed the power tube pins with some cleaner, worked em around in the sockets for a little, cleaned em off, and repeated a couple times...no more noise.

    i think i will be getting one of those cap testers though. any suggestions?
     
  4. Swarty

    Swarty Member

    Messages:
    1,132
    Joined:
    Dec 16, 2003
    Location:
    Michigan
    Decoupling caps and filter caps are the same thing.
     
  5. dix0r

    dix0r Guest

    hah, i never knew that.

    thanks :]
     

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