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Blown guitar amp! SOS!

Discussion in 'General Electronics Discussion' started by Pharaday, Apr 26, 2016.

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  1. Pharaday

    Pharaday

    138
    4
    Jan 18, 2016
    So, I took my Fender Frontman 15G guitar amp over to a buddy's house and when I plugged it in, it made some weird buzzing noises, so I turned it off and it would never come back on. I investigated and learned that when I unplugged it, the 3rd, grounding prong on the power cable stayed behind in my power strip and I had plugged it in with only 2 prongs. Bricks were shat. I checked the fuse and it doesn't LOOK blown, but you guys be the judge. I have enclosed a pic of the fuse. IMG_20160426_154037.jpg My brother bought me this amp, and I can't let him find out I broke it! Please! tell me which part of the amp you need pics of or what component of its IC I need to test to fix it! Do this and you will have earned a life debt! double e's, it's your time to shine!
     
  2. 73's de Edd

    73's de Edd

    3,105
    1,312
    Aug 21, 2015
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    Sir Pharaday (shield?) . . . . . . .


    Best as I can make out . . .still looks like a good slow blow fuse type to me.
    Now is the time when you use an ohmmeter to tell for sure.
    WHAT ! . . . . . . . . . no ohmmeter . . . along with minimal techno expertise ?
    Then . . . . . . . merely utilize cave man 101 procedure.
    Turn on a flashlight, unscrew the back battery access end cap and note that the light goes out . . . . due to loss of a circuit completion with a compression spring and that end cap being screwed on.
    Hold and PRESS one fuse tip to the center of the battery's exposed - case terminal, then use the BARE metal of the uninsulated end cap to bridge between the opposite fuse tip and the rim of the flashlight case.
    Compress inwardly to now simulate the missing spring .
    If the flashlight then lights again . . . . . . . .respond with a . . . . . . .Wheeeeeeeeeeeew.

    If you only had the amp and a guitar plugged in with no OTHER auxiliary equipment PLUGGED IN, to complete a power loop, I see no reason for the experience.
    The two AC prongs, plugged in via the initially present round ground guide pin, should be properly polarized to have still had a ground between one of those connections which is ALSO being a ground.

    You just now might be hypersensitive to hum pick up if you have guitar in hand and are touching any of its metal.

    Lay the guitar aside and see if the hum abates . . . or unplug it.

    If it silences . . . .work with repairing your AC plug end . . . . . particularly if you are a "power cord jerker".





    73's de Edd



    .
     
    BobK likes this.
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Two things right away:
    1 - The grounding plug is often for safety. No current is ever *meant* to travel through it. Devices should be able to operate without the grounding plug... although they may not be as safe to use! (Some older homes don't actually have a proper ground anyway.
    2 - You can't always tell a fuse is blown from looking at it. Please measure the resistance with a multi-meter to be sure. (It *looks* good... but always measure if you are unsure)

    Anyway... time for work.
    You can replace the cable or plug easily to restore the ground lead. The ground lead will help to eliminate noise and is most likely tied to the case of the amp. It should not have caused a fault in the amp. After measuring the fuse, it's time to share model numbers, and a picture of the inside of the amp if... but only if the fuse measure good!

    Let us know, many of us can help
     
  4. Pharaday

    Pharaday

    138
    4
    Jan 18, 2016
    Oh my Jesus yes OK the fuse is blown. AMERICA BREATHES A SIGH OF RELIEF! Using my multimeter and as much tech experience one might expect a CE w/ all his circuits done to have, I measured infinite resistance on the fuse and to be sure, I attempted to power an LED through it. Not sure I have that same fuse. Its 500mA/250V. Which other fuses will do or do I need that exact same one? I'd prefer not to bypass the fusehole, which is the technical term for that, a fusehole.
     
    Gryd3 likes this.
  5. Gryd3

    Gryd3

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    Jun 25, 2014
    Never bypass a fuse unless you are absolutely certain you know what you are doing...
    The fuse popped for a reason, it could be age, but could also be something *else* wrong inside... buy an exact match for the fuse and replace. Observe carefully when you turn it on. If the new fuse pops, something else is wrong and it's time to dig in.
    Be certain that you don't put a fast acting fuse in-place of a slow acting fuse or the other way around. Fuses should always be matched. The cap of the fuse holder, or the book should confirm the fuse rating... (Sometimes people use the wrong size fuse because it's what they have on hand at the time)
     
  6. 73's de Edd

    73's de Edd

    3,105
    1,312
    Aug 21, 2015
    .



    Sir Pharaday (shield?) . . . . . . .

    Blown guitar amp! SOGA!


    Since you are Amerikanski and not using 220VAC the o-fish-ul Fender schematic sez your unit uses a 500 ma fuse.
    [​IMG]

    BUT since you have a blown fuse . . . . .but not HEAVILY BLACKENED internally, best you initially use a table lamp with 60 watt incandescent lamp, using test lead clips to pass AC power through the lamp INSTEAD of the fuse.
    That will then tell you of serious circuitry problems that was the REASON for that BLOWN fuse.
    An immediate FULL brightness of the lamp at power up, would signify that .
    Normal indication would be for an initial slight glow and a dimming. . . . . . then you might be safe to try the fuse.

    In further looking at the amps AF output circuitry . . . . has me classifying that unit as a "strumming" amplifier . . . . with no wall shaking HEAVY beats.


    73's de Edd



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    Last edited: Apr 27, 2016
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    to the above advice let me add "very carefully so as not to electrocute yourself".
     
  8. Pharaday

    Pharaday

    138
    4
    Jan 18, 2016
    Roger. STOP. you guys rock. STOP. Roffle @ amerikanski, We're all garbage, Also acceptable is murricunf***yea. STOP.
     
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