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do have I have to change my guitar amp's zener diodes?

Discussion in 'Electronic Repair' started by [email protected], Apr 1, 2006.

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  1. Guest

    HI all,

    I've no experience in repairing or in electronics but I opened my amp
    to change an input jack and noticed this:

    http://img360.imageshack.us/img360/8841/scanimage0012tf.png

    http://img451.imageshack.us/img451/6885/scanimage0047pi.png

    http://img84.imageshack.us/img84/7444/scanimage0024my.png

    It looks like zener diodes have burned the board under them.

    The amp works great, the sound is ok, should I change them?

    here is some schematics I found:
    http://img84.imageshack.us/img84/4839/schemaparz6bm.png

    here's the zeners' pdf:
    http://www.ortodoxism.ro/datasheets/eic/1N5368A.pdf

    thanks for your help

    PS: sorry for my english...
     
  2. Tim Schwartz

    Tim Schwartz Guest

    Hello,

    First, don't panic. I'd measure the voltage(s) and see if it(they)
    is(are) correct. They are certainly running warm, as they have baked
    the board a bit, and they are near some high wattage resistors. If the
    voltage is correct, you could leave them alone.

    If you want to replace them as a precaution, I'd solder the new one is
    spaced up off the board a bit so that they get more cooling air around
    them, maybe .25 in or so. Be very careful, as when they bake the board
    like this the solder foils can get fragile.

    Regards,
    Tim Schwartz
    Bristol Electronics
     
  3. Arfa Daily

    Arfa Daily Guest

    All agreed with Tim. What you have there is what typically happens when this
    simple power resistor / 5 watt zener arrangement is used to derive the + / -
    15v ( or whatever ) supplies for the front end opamps, from the + / - 50v
    ( or whatever ) rails for the power amp. I see it all the time.

    If you really want to do something about it, just check the state of the
    joints on the other side of the board. You will probably find that they are
    quite crystalline, so may benefit from being reflowed with some new solder,
    before they start to go intermittent ( which of course, they will, at the
    most inopportune time, right in the middle of a gig !! ). But as Tim says,
    be a liitle careful of the track foils, as they will probably no longer be
    bonded to the board very well.

    Arfa
     
  4. Smitty Two

    Smitty Two Guest

    No. If it's working great, leave them alone, particularly in light of
    your inexperience. The older and more corroded and crispier something
    gets, the more difficult it is to work with. (you can check with my g.f.
    about that) If you don't have good tools and a reasonable amount of
    soldering experience, it's as likely that something will go wrong as it
    is to go right. Then a simple job becomes not simple.
     
  5. Jamie

    Jamie Guest

    looks normal for acheap/bad design.
    if it really bothers you?, buy new diodes
    and new cement resisters and mount them with
    longer legs so that the units are not near the
    board.
     
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