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Discussion in 'Amps and Cabs [BG]' started by burns_isaac, Jul 9, 2013.

  1. burns_isaac


    Jun 5, 2010
    My Ampeg burned up the other day at a gig. I pulled it apart when I go home and found the fuse was so burned there was zero filament left, the switch was burned up, and then after I jumped it to run one more test I found smoke pouring out of one of three small rectangular things soldered to the board. What are they and this the problem. I'm including a picture. Thanks a ton! ImageUploadedByTalkBass1373392188.460100.jpg
  2. BbbyBld


    Oct 13, 2005
    Meridian, MS
    MI Amp Engineer: Peavey Electronics
    Those rectangular things are resistors, specifically, 5 Watt wire-wound ceramic power resistors aka "bathtub resistors" because that's what they look like. If a resistor like that burns up, you have a pretty serious problem, possibly a blown power amp. Obviously it will need to be checked out and repaired by a tech.
  3. Register_To_Disable

  4. Those are ceramic resistors.. I would suggest taking it to someone who can check the entire amp over to make sure those are not the only issues..

    As most will state, there is a lot of lethal voltages in an amp that can kill you if you do not know what you are doing...
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Those are wire wound power resistors. Usually the value is on the side that is against the board. Otherwise, the schematic (Loud can email you one if you supply the amp's serial number) will tell you what the value is.

    Replacing the one that is burnt might fix your problem, then again it might not. The resistors, in addition to being a resistor in the circuit, act like a fuse. They will blow if too much current is running through them. This could be because what it is connected to has a problem. In acting like a fuse, it protects your amp from more costly repairs.

    Sometimes the resistors simply blow when they get old or if they have a fault. In those cases you simply change them.

    A tech should look at it.
  6. burns_isaac


    Jun 5, 2010
    The resistor that burned up is a PW-3. The other two are PW- 5A. Should they all be 5A?
  7. burns_isaac


    Jun 5, 2010
    My issue is I have 6 hours to either get it up and running for a gig tonight or buy something else.
  8. Rbucket76


    Apr 15, 2013
    Portland, OR
    I can almost guarantee you have a critical failure in the power amp. The power transistors probably shorted. Resistors do not smoke unless something is drawing current through them. The fuse blows as a protection. If you don't have time to get it to a tech, rent something else for your gig. Don't try to do anything yourself.
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    PW-3 and PW-5 three and five watt resistors. Here is the data sheet.

    Unless you can have a tech look at it right away, I would try to borrow or rent an amp for the gig. Call a music store and see if they can help you out for tonight.

    The problem can be more complex than simply just a blown component. Replacing the parts without checking out the rest of the amp could result in damage to other components. So be careful.
  10. +1
  11. AstroSonic

    AstroSonic Supporting Member

    Dec 10, 2009
    rural New Mexico
    That 3w ceramic resistor is in series with the -40v supply on the output stage. Very likely, one (or both) of the output transistors is blown (shorted). A tech will have to repair this. Do not try working around this, as more damage will result.
  12. B-string

    B-string Supporting Member

    If a fuse blows it usually has a very good reason. NEVER "JUMP" a fuse. It is now possible you fried the speaker as well. Get something else for your shows.
  13. burns_isaac


    Jun 5, 2010
    Alright alright well luckily I can't find the correct sized resistors anywhere. Thanks gentlemen! Rental it is. The thing has obviously been repaired before considering the massive gobs of silicone all over the solder connections. It may be time to put this guy in the scrap box
  14. burns_isaac


    Jun 5, 2010
    The switch was also burned up. The wire connection had soldered itself to the power switch connection so yeah Im sure there is something severely going on here. Thanks for all the help!
  15. two fingers

    two fingers Opinionated blowhard. But not mad about it. Gold Supporting Member

    Feb 7, 2005
    Eastern NC USA
    It is probably just as well. As far as components go, it is rare that a resistor just "goes bad" by itself. (Certainly not impossible, but improbable.) Almost always something nearby CAUSED it to burn up, short out, etc.

    It could still be something simple though. I wouldn't scrap it either.
  16. Sometimes the output transitors are really OK,
    but a driver stage before them is shorted.
    Either way, it tends to put large amounts of DC into the
    speaker voice coil, which will normally burn up, before a fuse can blow.
  17. burns_isaac


    Jun 5, 2010
    Ok to get into a deeper description, for the past month the panel that the board is attached to has been getting really hot, not just warm but I mean HOT! So at the gig the whole unit turned itself off in the middle of performance and that's when I noticed the distinct smell of burning electronics. I immediately went to unplug it and the chord itself was pretty warm which I know for sure should never happen. That's when I loaded it up, went home, opened it up, and discovered the burned up resistor, fuse, and switch.
  18. B-string

    B-string Supporting Member

    It is done without major repairs. BTW the glue you see on those resistor leads is factory to keep vibrations on large components from breaking the solder connection on the PC board.
  19. AstroSonic

    AstroSonic Supporting Member

    Dec 10, 2009
    rural New Mexico
    +1 When a resistor goes it is almost always an indication that another component with which it is connected has gone bad. Resistors generally burn up when too much current passes through them.

    Given that this involves the output stage, which is directly coupled to the speaker, the speaker may be fried (as mentioned by Bill_Whitehurst).

    Get an estimate from the tech (probably cost a half hour or so of tech time), before proceeding with the repair. A new switch, output transistor(s) (may need to get a matched pair), speaker and labor could end up being pretty expensive relative to the cost of a new replacement amp.
  20. burns_isaac


    Jun 5, 2010
    I bought the thing used 5 years ago for $280 and I believe it's a 1994 model. Pushing 20 years old something was bound to go wrong!