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...

  2. JamesPeters

    JamesPeters Member

    Jul 3, 2002
    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 more noise.

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

    Swarty Member

    Dec 16, 2003
    Decoupling caps and filter caps are the same thing.
  5. dix0r

    dix0r Guest

    hah, i never knew that.

    thanks :]

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