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what is this part and why is my amp smoking

Discussion in 'Amps and Cabs [BG]' started by TheEnthBass, Jun 5, 2014.


  1. TheEnthBass

    TheEnthBass

    Apr 9, 2010
    Connecticut
    I enjoy a smoke now and again but this brand is harsh. My Carvin B1500 had been super reliable for several years, and then, I noticed a burning smell on stage. Well, really, I got through the show and the keyboard player told be about it after. So i was cleaning some connections up, getting dust out, and then plugged it in and the amp protect light came on, had some noise present when volume knob was turned, fan hit double time and smoke came out. I shut it down. I pulled the power module and see a songle sru-24vdc-sl-c that appears a little burnt but nothing else appears to be damaged. what is this part? is that my culprit or a symptom of a bigger issue?
     
  2. Mr. Foxen

    Mr. Foxen Commercial User

    Jul 24, 2009
    Bristol, UK
    Amp tinkerer at Ampstack
    I'd guess symptom. Proper tech time.
     
  3. Johnny Crab

    Johnny Crab ACME,QSC,Fame/Hondo/Greco/HELIX user & BOSE Abuser Gold Supporting Member

    Feb 11, 2004
    South Texas
    If you've been to tech school and can find the schematic AND have a true RMS meter, signal generator, dummy loads, and o'scope....go for it.
    If not, tech time because you let the smoke out......
    In a previous lifetime, my SVT would get rebuilt(power supply section mainly) about once every 2 years by me and guitar folks would bring their Marshalls, Fenders, etc. to me to hot rod(before factories put in master volumes).
    Now?
    I only spend time on my own gear IF it is worth the time because there are fewer days ahead than there are behind.
     
  4. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Googling that part number, it's a relay. I'd guess it's probably the output relay, which serves a couple of purposes: 1) Activates the power amp output after the power amp has stabilized. 2) Cuts the output if there is a fault that might damage the speaker.

    Note my comments assume someone who is qualified to work on gear.

    If the relay itself burnt up, then it was probably defective all along. Some relays have a plastic cap that you can pull off and inspect the innards. There may be a bad solder joint around the relay. The smoke may have come from somewhere near the relay. On the other hand, the protect light suggests that something else went wrong.
     
  5. TheEnthBass

    TheEnthBass

    Apr 9, 2010
    Connecticut
    well... I might swap the relay and pray that the source was a power issue from the wall etc. the relay is only a few bucks and easy to swap. if not I'll suck it up and use a tech. back to the old ampeg tubes for now. not so bad I guess. so much for the consistency of solid state gear though i guess the repair on the carvin vs the cost of there tubes on the old gear is comparable. :confused:
     
  6. TheEnthBass

    TheEnthBass

    Apr 9, 2010
    Connecticut
    the protect light would come on.if under relay was failing though right...
     
  7. Usually the parts that burn are NOT the part that failed. Many amps have resistors in places to act similar to a fuse --- for example when one transistor blows, it can take out every other transistor in the chain - and a good amp design will usually have a resistor in a spot where it will sacrifice itself (burn out) and save the rest of the transistors from death. In that case replacing the burnt resistor and powering up the amp again would just burn up more parts in the chain. (just as an example --- no idea what your situation is --- but this sort of thing is common in amp designs)
     
  8. It's not a power issue from the wall.

    Randomly replacing parts isn't a very good repair method. Every time you power it back up, more parts can burn up. A good tech would get the schematic http://www.carvinservice.com/crg/schematics/B1500.pdf , test some basic stuff without burning more stuff up, and fix it.
     
    Last edited: Jun 5, 2014
  9. TheEnthBass

    TheEnthBass

    Apr 9, 2010
    Connecticut
    true but when the tech cost its more than half the price on the unit I'll take my chances though I understand the odds. tough call. if I run the new relay under controlled conditions and am ready to shut it down it may stand to reason that I can catch the problem at the same stage...
     
  10. By the way, when somebody brings me an amp in to fix, and I see that they've already attempted to repair it themselves, my repair estimate gets increased substantially. Because I have to start tracing out further damage that may have been done by their "repair".
     
  11. OldPlucker

    OldPlucker Supporting Member

    Apr 5, 2014
    Maryland
    Go to you local electronics store and buy a can of magic smoke. You're not supposed to let it out of the amp.
     
    BioWeapon likes this.
  12. TheEnthBass

    TheEnthBass

    Apr 9, 2010
    Connecticut
    for the record i'm aware that i'm neither knowledgeable or skilled i'm hoping limited logic and done luck might save a few bucks.
     
  13. No you won't. Output transistors will fry faster than your fingers can flip the switch.

    Your call though.
     
  14. TheEnthBass

    TheEnthBass

    Apr 9, 2010
    Connecticut
    wouldn't the output have burnt already then? tough call.
     
  15. Not a tough call for me! The protection circuit *may* have saved the outputs from a dead short. By replacing the relay and powering it up again the protect circuit will be tested to its max AGAIN and this time it may not kick in in time.

    Even if your estimate of "the repair will cost half the amp" is true, that's still half the cost of a replacement amp. Continue to try to power up the amp without taking appropriate troubleshooting steps, and the repair will cost more, perhaps the cost of a new amp!

    I gave a link to the schematic. A good tech can isolate your problems pretty quickly from there.
     
    Winoman and dincz like this.
  16. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    This is gonna be good!
     
    tbz, Darkonar, Winoman and 1 other person like this.
  17. delta7fred

    delta7fred

    Jul 3, 2007
    England
    +1

    I hate it when this happens, a good friend of mine thinks he is an electronics expert so always "has a go" himself before bringing his amps and lighting equipment to me. Being a good friend I don't charge him but I certainly complain about the mess he has made.
     
  18. Hi.

    AFAIK Lucas (The Prince Of Darkness) is the only company that You can get the magic smoke for as well as the kit to inject it back to their systems.
    No such luck for other companies products :(.

    Regards
    Sam
     
    kcole4001 likes this.
  19. I would be willing to bet this is the case. Thanks to Bill for linking the drawing, I'll look at it in the morning. Relays go bad, usually with increased resistance across their contacts by corrosion (but sometimes the 'signal' coil goes up in smoke-this is more rare). Bad contacts eventually result in a very high resistance across those contacts, creating smoke. I agree--I'd replace it and try again. Relays are always spec'd well above the current they're expected to see. If it were a deeper problem, other components would have blown up long before the relay got hot. Betcha.
     
    Last edited: Jun 6, 2014
  20. The OP said the Protect light is on. Looking at the schematic, a blown relay coil, or contacts, would likely not cause the Protect light to come on.
     
    BioWeapon and agedhorse like this.

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