First big mistake!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by brad347, Aug 5, 2006.


  1. brad347

    brad347 Member

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    So I was tracing down a crackly sound that was intermittent in the pro junior. The chopstick test revealed nothing. Noise disappeared when I removed the phase inverter, but not when I removed any other tube on its own.

    So, I started shorting things to ground with a test lead. Well things are a little tight in there and I was working around the phase inverter and accidentally shorted a part I wasn't supposed to! Between C11 and R26 on this schematic (yes, that would be right between the power tubes and output transformer HA HA HA! http://www.ampwares.com/ffg/schem/pro_jr_schem.jpg

    Well, when I switched the amp on, R26 went up in flames and I got a nice little light show. This happened instantly and my hand was still on the switch so I flipped 'er off as fast as I could. The whole thing probably took less than one second from power on to power off.

    Hopefully that's not long enough to majorly fry anything. I decided that it's time for me to take a BREAK from this thing to get my head straight. Obviously I wasn't thinking clearly when I did THAT little move. Incidentally, the little 1/2 watt resistor, though charred, still reads very close to within 20% of its rated value! I'll replace it and C11 too for good measure (though it looks fine) and hopefully I should be okay. There was a little scorch mark on only the top surface of the circuit board which I cleaned off very carefully and now it looks good as new. Trace side of the board is fine.


    SO, congratulate me on my first big really stupid mistake, i've been tinkering with amps for a year now and never majorly f***ed up until now, and I didn't even get shocked. I think that's cause for celebration. :dude
     
  2. brad347

    brad347 Member

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    oh yeah, PS... while I was digging out the charred resistor I found a little scrap of stranded wire that was probably intermittently shorting or arcing between two leads and was probably the cause of my problem all along. DOH! I guess that just ADDS to the stupid factor!
     
  3. Dave C

    Dave C Gold Supporting Member

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    Congrats and welcome to the club....everybody does that at least once. No harm....no foul , but try to be a little more careful next time. And I thought I was the only one ....hah.
    Dave C
     
  4. Riscchip

    Riscchip Member

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    I've done worse, hehe. For example, I recently accidentally replaced a bunch of 600v rated wire in one of my amps with 300v wire. Beat that for stupid.

    :rolleyes:

    (why, you ask? The electronics place told me it was the same rating as the 600v sample I gave them to match. Did I check before installing? No, I did not. :( )
     
  5. esoteric pete

    esoteric pete Supporting Member

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    you should send that pro jr. chassis to steve scoott @s2amps.com and have him convert it to a P2P wirer deluxe....



    sorry...i had to...he does great work and im very happy w/ my pro. jr. conversion that he did for me a while back...
     
  6. brad347

    brad347 Member

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    thanks pete but I love my amp how it is. Nearly every component inside has been changed including the transformers and speaker and it really sings like a bird. I have a 'real' PTP deluxe already :D
     
  7. Hacksaw

    Hacksaw Time Warped Gold Supporting Member

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    a wise man ( my father) told me a long time ago.. visual inspections! as usually you may find something that way first. I spend a lot of time just looking over things with a BIG magnifing lens! amazing things learned when I listen! I remember my first goof. chassis had me doing the dance! oops.. start over. what did I do wrong. haha.. Ok, ?? back to the visual inspections.

    Thanks dad ;-)
     
  8. jbltwin1

    jbltwin1 Member

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    I guess this is about the time that I admit to dropping a pair of cutters inside a Music Man amp while it was running. That 700 volts dosn't bounce around too long before it breaks things. I lived, the amp didn't. Maybe I'll fix that some day.
     
  9. brad347

    brad347 Member

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    hahaha this is better than a support group. :)
     
  10. hasserl

    hasserl Member

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    A good tool for doing this sort of thing is a harness with an alligator clip on one end, that goes to ground, a probe on the other end, that goes to the item to be shorted, and a 630 volt cap in the middle, .1uf should be fine. Attach the probe to a chop stick to insulate yourself from the harness. The cap will block any high voltage that you happen to touch with the probe preventing the sort of problem you had.
     
  11. TheAmpNerd

    TheAmpNerd Member

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    Hi Brad,

    Tell us how that made you feel?


    AND


    Thank you for sharing that with us.



    WATER ANYONE?


    :horse
     
  12. brad347

    brad347 Member

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    most excellent. You da man.
     

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