Connect with us

transformer blowing fuses

Discussion in 'Troubleshooting and Repair' started by barsukas, Dec 3, 2011.

Scroll to continue with content
  1. barsukas

    barsukas

    4
    0
    Dec 3, 2011
    My first post here, might be a stupid questions, sorry if it is.

    So, my amp keeps blowing fuses, i took the transformer out, tried to turn it on and it blew a fuse with nothing connected to the secondary windings. Resistance of the primary winding is about 105 ohms, and the fuse is 0.25A 250V, resistance of it is 16ohms. I am really new to electronics, but i think that the resistance of the primary winding is much smaller, than it should be.

    Is there a problem with the transformer or could there be something entirely different?

    [​IMG]
     
  2. alfa88

    alfa88

    329
    4
    Dec 1, 2010
    impedance

    Welcome to the forum.
    The value you speak of would be impedance not resistance. Think of impedance as an AC resistance . Compare the resistance of the other channel's transformer to verify the values are similar. My hunch is that it is something other than the transformer. A picture always work wonders here.
     
    Last edited: Dec 3, 2011
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    So how big is that transformer? At least it's smaller than 230V * 0.25A = 57VA. The resistance will depend on this.
    It's hard to use resistance as a measure of transformer health unless one has an identical transformer to compare with. Measuring inductance would reveal it though.
    An internal short may not affect resistance very much but will make the inductance very low.
    Does the transformer output DC? Did you disconnect the secondary DC or AC?
     
  4. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi there. i cant add much at the moment, the previous two posts say the way forward, only thing i can add is your reading of the primary winding, ive measured a lot of primary windings from all sorts of gear, those readings are nothing unusual so long as the transformer has no short in its primary side. :)
     
  5. alfa88

    alfa88

    329
    4
    Dec 1, 2010
    Clarification

    Are we talking about an output transformer or a power transformer?
     
  6. barsukas

    barsukas

    4
    0
    Dec 3, 2011
    It's a power transformer, outputs DC and i disconnected everything from the secondary winding, but it still blew the fuse. But I think I might have found the answer to my problem. Found a manual wich states that the amp needs a T type fuse, to handle the inrush surge i guess. Funny thing is, it worked without any problems with a F fuse, so when it blew i just got the same kind and then it blew three in a row. I'll get a T fuse and see if it works. Why it worked so long with F fuse before is beyond me...
     
  7. alfa88

    alfa88

    329
    4
    Dec 1, 2010
    Okay , that changes my 1st post. When you talked about 16 Ohms I assumed you were referring to an output transformer. Now I'm confused. You say it outputs DC? That can only happen if there is/are rectifier/s involved. Another thing: if, indeed, you have everything disconnected from the secondary there shouldn't be enough inrush current to blow a fuse. Providing that it is the correct Amperage. It sort of sounds like your transformer is bad. Picture please for all us armchair techs.
     
  8. davenn

    davenn Moderator

    13,674
    1,892
    Sep 5, 2009
    we still need to confirm if absolutely EVERYTHING is disconnected from the secondary and it still blows the mains fuse ??

    IF you still have the bridge rectifier connected then its most likely the rectifier thats died. Thats a pretty common fault
    IF not then there's probably a shorted turn in the transformer and it will have to be replaced

    Dave
     
    Last edited: Dec 4, 2011
  9. alfa88

    alfa88

    329
    4
    Dec 1, 2010
    Smell

    That DC output thing is what bothers me. One of the troubleshooting tricks I've developed over time is the x($) smell aka x(£) smell. A problem that is serious enough to blow a line fuse usually leaves a ;calling card. Sniff around. Unplugged please. :D
     
    Last edited: Dec 4, 2011
  10. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    Res, is who confused me, as I thought transformers only put out AC. If he is measuring DC then that would mean the rectifier is still attached and could possibly be the culprit.

    The 16 ohms alfa, was the resistance of his fuse I believe. Which says that the fuse is at least still functional.
     
    Last edited: Dec 4, 2011
  11. barsukas

    barsukas

    4
    0
    Dec 3, 2011
    Damn, sorry everyone, the transformer outputs AC, no rectifier, but i was writing that reply when i should have already been sleeping for some time, forgive me for that nonesense
     
  12. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Ok, with a disconnected AC secondary and a blown primary fuse I believe there are shorted turns somewhere in it.
    With the limited information given I couldn't take the word transformer literally, or for granted that it was an internal type. For all I knew it could be a "lump" on a wire.
    Since the transformer is so small I don't think it matters if the fuse is fast or slow. I'm afraid you're looking at obtaining a replacement transformer.
     
  13. barsukas

    barsukas

    4
    0
    Dec 3, 2011
    Latest news on this - got a T type fuse, tested the transformer without load on secondary winding and the fuse didn't blow. Gonna put the amp back together now and see if it still works. Right now i think it was just the fuse. Still no idea why the first F fuse worked for so long though...
     
  14. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Hm, strange.. It's not a toroid transformer is it?
     
  15. alfa88

    alfa88

    329
    4
    Dec 1, 2010
    Wait, wait, wait. Measure the AC on the secondary before you put it back in. You might glean a bit of insight as to the health of that transformer. Use clip leads and don't zap yourself. Without knowing too much about you amp my ballpark guess is you should measure around 40Vac.
     
  16. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    That might prove tricky, some amplifier transformers have multiple windings some times giving an output from the different windings, depends on amp and features the unit needs to power. :)
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-