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    power transformer problem - help?

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    Tom

    Posts : 166
    Join date : 2011-04-04

    power transformer problem - help?

    Post by Tom on Tue May 03, 2011 11:08 am

    SP-8 Preamp Kit. Built, was working, had a minor ground loop hum but not a big deal. Blew some fuses early on then stopped, seemed fine.

    Now blowing fuses all the time. I've taken all the secondarys off the board. Still blowing fuse.

    Disconnect the primaries, fuse holds. Connect the primarys back, fuse blows.

    Checked several times and circuit is correct (was working!) and can find no incorrect connections or shorts.

    Is it my PT? How can I check? I looked for shorts from primarys to secondarys and the extra purple ground and found none.

    Also took the PT out of the case and can find no evidence of damage or shorting to chassis. Even tried it outside the case with the same result, blows fuse.

    Any help appreciated. This is an Antek ASIT250 torroid.



    Bummin.

    tubes4hifi
    Admin

    Posts : 1284
    Join date : 2008-11-30

    Re: power transformer problem - help?

    Post by tubes4hifi on Tue May 03, 2011 11:53 am

    the primary windings should measure about 7.5 ohms each, try each one (they are usually wired in parallel).
    Maybe one or both of them has an internal short. The shield (purple) wire should read infinite resistance to any other connection.

    Tom

    Posts : 166
    Join date : 2011-04-04

    Re: power transformer problem - help?

    Post by Tom on Wed May 04, 2011 9:19 am

    OK, took apart the whole power supply side, desoldered, resoldered, cleaned up, etc.
    Fuse is fine now. I don't know why.

    This goes to show two things.

    1) If at first you don't succeed blah blah blah
    and
    2) I am an idiot.

    Very Happy Tom

    tubes4hifi
    Admin

    Posts : 1284
    Join date : 2008-11-30

    Re: power transformer problem - help?

    Post by tubes4hifi on Thu May 05, 2011 11:46 pm

    add #3, neatness counts, cause it's hard to find errors if it's not neat, that comes from my experience,
    hey, we all have messed up some things once in a while !!
    add #4, if it works, don't fix it
    add #5, if it doesn't work, start all over, and then do it right Very Happy

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