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HELP!!! SWR SM-900 ISSUE!!!

Discussion in 'Amps and Cabs [BG]' started by XPshychoticXPyr, Sep 8, 2004.


  1. I just got an SWR SM-900 really cheap but it has a problem when turned on if the top of the amps metal touches the inside (Head sinks) on the top left side of the amp it seems to make a large nasty pop/crackle. It is only when something touches the Heat sinks though. I opened it and tried it and it works perfectly except if the metal block inside is touched or poked. Help me!!!

    -Vince

    P.S. i am dumb they are heat sinks not power transformers...stupid teenagers!
     
  2. Waabs

    Waabs Employee, Musical Instrument Retail

    Aug 1, 2004
    Australia
    So you're saying the amp casing touches the top of the transformer? How does that happen?
     
  3. It sure sounds like the amp was dropped at one point. Maybe in a rack, so there's no obvious drop marks, but the transformer is heavy and may have jarred itself out of it's seating.

    You're saying that when the top cover of the head is screwed into place, the transformer hits it? First off, take the top cover off and rattle the transformer around, does it move? Does it attach to the motherboard or mounting studs on the bottom of the amp? Are any screws loose or bent or otherwise out-of-whack? If they are, try to re-bend everything back to where it's supposed to go. The transformer isn't supposed to touch the surfaces of the amp at all.

    Electricians use non-conductive insulating tape when they have to splice high-voltage wiring in a small junction box. They splice the wires, then wrap the splice in a ball of the insulating tape which gives it 'padding' and protection because it will be tight in the box. Look into putting some of this tape on the inside of the top cover over the transformer. The stuff I've seen looks like a roll of electrical tape (black rubber tape), but it's about 1/8" thick.

    ps. I don't have a yahoo account and don't really want to get one, so I can't see your picture.
     
  4. Its not bent or loose but i will try the non conductive take thanks man.

    -Vince
     
  5. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    Could you turn Yahoo's album sharing on so that we can see the pics?

    My SM900 has a decent amount of clearance between the top plate and the tranny... Maybe the reason it was cheap was that someone jammed a transformer in there that doesn't belong there. Which leads me to wonder whether that amp will function to spec... :confused: just wondering out loud...

    Regardless, PLEASE BE CAREFUL, there is definitely something wrong there and you are dealing with the shock worthy parts of the amp.

    Keep us informed.
     
  6. http://photos.yahoo.com/topgunebay Try that link.

    -Vince

    P.S. even with the amp cover on and unscrewed it makes a low grumble at times through the cab...hmmm im gonna call SWR.
     
  7. Its the heatsinks that is the issue guys i labeled it wrong and though it was a transformer...i know i know im an idiot teenager.

    And also is i put the cover back on and tap around the top left corner it clips aswell...

    -Vince
     
  8. bigbeefdog

    bigbeefdog Who let the dogs in?

    Jul 7, 2003
    Mandeville, LA
    XPXP, please proceed with an abundance of caution. People have been electrocuted - as in DEAD - by electrical shorts of this sort. Even holding your bass while plugged into this unit might not be safe. Pressing on the unit and causing the "crackle" assuredly isn't.

    Unplug it and bring it to a well-regarded repair tech ASAP.
     
  9. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    I had a similar problem with an old SM400 of mine. Intermittent crackling and distortion when one of the heatsinks were shorted to ground. I took it to a couple of techs who reported "no problems" with the amp. It was infuriating.

    Finally, I enlisted the help of my father, who has an EE degree from the late 60's, to investigate the problem.

    Turned out that the biasing transistor for one of the power amps developed a shot within itself, from one of the legs to its casing, which is attached to the heatsink. If there are any spots on the heatsink where the non conductive paint has worn off it casues a short to the chassis, thereby starving the power transistors of juice...

    Anyway, it took us about 20 hours of poking around (as well as me getting jolted twice, not fun) to figure it out. Once we figured the problem out, it took 15 minutes to fix, a straight swap of one transistor. Amp has been running perfectly ever since.

    It may not be whats going on there but thought I should mention it.

    Let me know if you want more details.
     
  10. waxcomb

    waxcomb

    Jun 29, 2003
    Martinez, CA
    Dump it and buy Mesa. It worked wonders for my sound.
     
  11. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    Wow, how helpful. If it turns out he can fix it for $25 and have a working amp (which may be -gasp- to his liking) it makes more sense than dumping it on account of your brand loyalty. Furthermore if he decides to sell at some point he'll get more towards his next amp if the 900 is fixed.

    :rolleyes:
     
  12. waxcomb

    waxcomb

    Jun 29, 2003
    Martinez, CA
    Sure. Fix it, sell it and then go Mesa. :mad: :meh: :cool:
     
  13. Ive got a mesa m2000 i was gonna sell this so i could get some more money towards another buy i wanna make shortly. So how can i fix this anyone know?

    -Vince
     
  14. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    Pics still ain't working...

    Take it to a tech and among other things have him check the transistors on the power modules for short circuits.

    There really isn't a simple fix...