1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
     
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

replacing transformer in MAG amp

Discussion in 'Amps and Cabs [BG]' started by stew582018, May 15, 2018.


  1. stew582018

    stew582018

    May 15, 2018
    Hi all, sorry if this question is in the wrong place.

    As the heading says, I need to change the Toroidal transformer in my amp,
    (it's a MAG 400, model 410T 400)

    replacing it will be the easy part, but finding one, now thats the hard part.
    had a look on the unit and there is no indication of the output voltage or current,
    so replacing it with another transformer with same values is not going to be possible without a schematic to see the values.
    any help / advice appreciated.
     
  2. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Why are you wanting to replace the power transformer?
     
    john m and agedhorse like this.
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Maybe it's "bad", along with "bad" caps ;)

    Must be a rash of bad transformer, bad cap threads on the internet this week!
     
    Spidey2112 and BassmanPaul like this.
  4. RECAP RECAP RECAP!

    :laugh::D:laugh:
     
    agedhorse likes this.
  5. Spidey2112

    Spidey2112

    Aug 3, 2016
    I love this cap...

    2018-05-07 18.51.02_1.
     
    agedhorse likes this.
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I’ve never seen a schematic available publically for your amp.

    Sometimes the Ashdown transformers have the top metal cap that holds it in place overtightened. This can lead to physical hum problems and even damage to the windings which can cause a short to the chassis.

    If there is no obvious visible issue, disassembling the mount and inspecting the transformer and insulating pad may provide some insight. Sometimes the transformers can be repaired.
     
    Last edited: May 15, 2018
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Definitely a DIY project, along with other "hold my beer, watch this" activities. ;)

    When working on any power transformer, it's a REALLY good idea to verify proper safety and isolation with a HI-POT test to be sure there are no safety issues that could hurt somebody down the road. This would be the classic poster-child for doing so.
     
    beans-on-toast likes this.
  8. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I was suggesting a course of action to help determine what the issue may be, not who would undertake it.

    I’m surprised by the number of Ashdown toriod related problems that keep coming up. There has been no indication if this is an older UK manufactured unit, which from what I’ve see have lower fairure rates, or a later Chinese one.
     
    agedhorse likes this.
  9. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    OP, Forgive my manners. I just noticed that you joined today so may I be the first to welcome you to Talk Bass. :D

    That said, what’s wrong with your amp that leads you to believe that the power Toroid needs to be replaced.
     
  10. stew582018

    stew582018

    May 15, 2018
    Hi Paul, transformer is knackered, power in but nothing on the secondary, no indication of output voltage / current on the toroidal so kinda stumped :(

    thanks Beans on toast,
    all looks fine in this regard, unit was not over tight, and the rubber pad at bottom is in good shape, as in the (look of) the transformer.
    No idea of the age of the amp sorry, I got it second hand a few years back
     
    Last edited: May 16, 2018 at 2:52 AM
    beans-on-toast and radbass like this.
  11. john m

    john m Supporting Member

    Jan 15, 2006
    Most likely custom.
    Most likely not the problem.

    Electronic repair is not the same as replacing parts.
     
  12. Maybe Ashdown will sell you a replacement?
     
  13. my ashdown is broke too. same model.. just kinda popped and very very low volume and then nothing..i have it for sale on reverb
     
  14. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If all the secondry windings are not working, then there is a good chance that the problem is in the primary. A fuse or varistor may have blown open on the primary side.

    The first step that a tech would normally take would be to isolate the transformer. Disconnect the primary and secondary, using a variac and current limiter, take voltage readings at both the primary and secondary. This tests the transformer under no load. Without a schematic it will be difficult to know what wire colors go with which windings. The PCB has labels otherwise circuits would have to be traced at the connectors.

    Ashdown amps tend to be very well fused on every power winding before rectifiers. A short in a circuit after the transformer would have blown one of these fuses.
     
    BassmanPaul likes this.
  15. stew582018

    stew582018

    May 15, 2018
    Ta all,
    fuses were the first thing i had a look for,
    given that there is voltage into the transformer and nothing out localizes the fault,
    removing the transformer and taking wrapper of the toroidal is my next step, get a better look at the outer winding's that way.
     
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Note that the wrapping material is an essential part of the safety system.
     
  17. byacey

    byacey

    May 16, 2008
    Alberta, Canada
    A simple resistance test will determine if the primary or secondary winding is open.
     
    BassmanPaul and ddnidd1 like this.
  18. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I can see this not ending well!! :(
     
  19. byacey

    byacey

    May 16, 2008
    Alberta, Canada
    I would hold back on dis-assembling anything until you narrow down exactly what the problem is. You're likely to create more problems and / or safety issues by blindly tearing into things.

    The secondary is least likely to be open as it's usually wound with heavier gauge wire, and also cools better because it's the outside winding. Also, if it's center tapped, both windings and the center tap lead would have to be completely open from each other to yield absolutely no output on any of the secondary windings. This isn't very likely unless something catastrophic happened to the amp.

    I would be looking at the primary winding continuity first.
     
    Last edited: May 17, 2018 at 12:41 PM