Biasing mishap story!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockon1, Feb 2, 2008.


  1. rockon1

    rockon1 Member

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    Didnt want to post it because I felt it was a dumb mistake but it was really just an accident. While I was biasing my supersonic and measuring my plate voltage I accidentally slipped with the probe and it momentarily hit pin 2 at the same time. A puff of smoke was released and the fuse blew. Replaced it and the amp worked fine however I knew something got damaged/very hot. Didnt see at the time where it came from but was pointed in the right direction by John Philips (to whom Im deeply indebted !) and saw that two resistors to ground got heated up pretty badly.

    I decided it was time for my very first PCB soldering job! Watched a video on desoldering and went to Radio Shack. I purchased a cheapo desoldering gun,some 100ohm 1/2 watt resistors and a new 15/30 watt soldering gun. Removed the board and desoldered the burnt looking but (still working resistors). Placed the new ones in,cut them to length and soldered them in. I doubt a tech could tell they were replaced. Alls well that ends well. Man I love the people here willing to help out the less educated! Again thanks John! Bob


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  2. Dave

    Dave Member

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    I'm just glad you weren't injured, Bob.

    I commend you for having the courage to fix it yourself. I would have ran to a tech without a second thought.
     
  3. frankencat

    frankencat Gold Supporting Member

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    I have done the exact same thing myself before and I learned my lesosn. Please people, use clips when you do this and you won't slip. It's cheap and simple insurance. Glad you weren't hurt. :)
     
  4. twinrider1

    twinrider1 Member

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    Thanks for sharing.
    I want to get into my amps, but I'm taking my time. I've been measuring resistances and comparing the real thing to the schematic; just getting to know things better. Before I test any voltages, I'm going to buy some alligator clips for my meter. (I want the kind where the barrel threads on, but Radio Shack doesn't carry them).
    I think I'll try my hand at making an adaptor to check the bias. Weber is asking $35 + s/h. Should be a good soldering practice.
     
  5. twinrider1

    twinrider1 Member

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    Are the clip leads a good way to go?
    https://amptechtools.powweb.com/clip.htm

    I've been looking for screw-on alligator clips for my meter leads but they're hard to find locally.
     
  6. burner

    burner Member

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    I've never slipped with a probe but that's probably sheer luck.I should probably start using clips.

    On a related note....
    I was discharging caps in a Marshall using the "screwdriver" method and everything was fine except for the fact that a finger on my other hand happened to be inadvertantly touching the chassis.
    That sucked....REALLY sucked!
     
  7. frankencat

    frankencat Gold Supporting Member

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    That's pretty much what I use.
     
  8. rockon1

    rockon1 Member

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    Well Ive wanted to do a little PCB component soldering for a while now. I watched a video and that gave me the incentive.

    http://www.solder.net/technical/tip25.asp

    The right tools for the job and it was easy-really. Oh yeah I made sure the caps were discharged first! It feels good to be able to DYI. Bob
     

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