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Thread: oh dear, whammy, what did i do?

  1. #1
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    oh dear, whammy, what did i do?

    so,
    i was messing around with my whammy 4 pedal.
    i put in the true bypass mod and all went well.

    however, when i went to put the LED in too, i tapped the power from under on of the regulators(?) but managed to short it when i turned it on

    i touched two of the pins together and there was a spark

    so... my question is... have i ruined my pedal now or do i just need a new regulator?

    how can i check?

    any help would be greatly received, i feel like a right idiot now.

  2. #2
    Supporting Member Jazz P Bass's Avatar
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    new regulator

    Can you identify the part number of the part in question?
    More specifics would be a big help.

  3. #3
    Noodle of Reality Steve Conner's Avatar
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    Have you tested the pedal to see if it still works (after removing the short of course)

    Voltage regulator ICs have all sorts of protection and can typically survive a short just fine.

    However, if you shorted the input pin to the output, the following circuitry may well not survive having 9V applied to it when it was designed for 5.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  4. #4
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    i will try it now.
    there is definitley still power in the circuit board but the regulator just gets hotter and hotter while its powered.

    if you are familiar with the whammy, all the controls and led's are on the right.
    this section used to flash then settle on the last selected harmony. now it flashes but just goes straight of and doesnt light up again.

  5. #5
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    yea.
    the true bypass works
    the signal is louder when the pedal is on but the controls dont light up and i cant change the sound

  6. #6
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    also,
    the common/ground is the centre right?
    i think... hope, i bridged one side to ground thats all

  7. #7
    Noodle of Reality Steve Conner's Avatar
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    Oh well, time to:

    Identify the part number of the offending chip

    Order a replacement

    Fit it

    Hope it works


    The centre pin is common on 78xx positive regulators. On the 79xx negative ones, it's something else.

    Shorting the output to ground won't blow the regulator, but shorting the input to ground sometimes will, if there's lots of capacitance on the output.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  8. #8
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    ok
    well there are two regulators in big heatsinks. i replaced one (7805 ct) with a 7805 i had.
    the other one is bigger. i guess i should just get it out
    is there a way to check wether or not its definitely broken?
    or is the excessive heat enough of a telltale sign?

  9. #9
    Noodle of Reality Steve Conner's Avatar
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    I assumed you'd have checked to see which of the two regulators was overheating, and replaced that one.

    But then you don't really know. Regulators often run hot when they're working. Maybe the one that's getting hot is the good one, and the busted one has gone cold. So might as well replace them both.

    You could probably test a 7805 with a 9V battery and a voltmeter, just apply 9v and see if it produces 5v. Though you really should connect an electrolytic cap between Out and Common, and another between In and Common, to make it a fair test.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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  11. #11
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    volts hrts?

    i did some probing.

    the 7805 i believe is reading ok. theres quite a bit of info bout that one on the net.

    the other one however has a different pinout.
    the ground isn't pin two so i shorted the in to the out.... :-0

    now, presuming the now broken regulator isnt pulling the voltage down at the input somehow(?) its getting 9v... its only putting out 0.5

    my question is.. how likely is it that i have damaged the following circuitry?
    i am assuming the next components were meant to be fed between 3 and 6 volts? would they they survive a jolt of 9??

  12. #12
    Supporting Member Jazz P Bass's Avatar
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    Part Numbers

    Can you please supply us with some part numbers?
    The "other one" may be a 7905 which is a negative voltage regulator.
    Pin #1, on the left, is 0 volts, or ground if you will.
    The center tab is input, the right pin is output.
    Then again, if the part is like you pictured above, LD33V, that is a 3.3 volt regulator.
    The left pin, #1, is ground. The center pin is Vout, the right pin is Vin.
    Attached Files Attached Files
    Last edited by Jazz P Bass; 11-22-2009 at 11:02 PM.

  13. #13
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    hey jazz
    the other one, as i called it. is the one in my first link above. i took a pic because i didnt know which bit was the part number.

    i have searched seperatley for all the combinations of letters on there and had most luck with 'LD33v' as the search criteria, at least that brings back results.
    so thats fine, yes that is the part.

    but, presuming what i did when i shorted it was jumper the input voltage directly to the output, and that i fit a replacement.

    i was just asking... what is the likelyhood the following circuitry will be ok after an unregulated 9v passed through them? is there an average volt limit or threshold for ic's and chips?

    i understand the answer wont fix my pedal...
    it will further my understanding tho

    thanks

  14. #14
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    also,
    i'm looking for the part (my picture) of a '-3.3v' or a '+3.3v' version?


    i looked at the chip info and searched for a 'LM7905' but they all say its a '-5v' output.

  15. #15
    Supporting Member Jazz P Bass's Avatar
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    LD33V

    Forget the 7905 if it is not on the board.
    The picture of LD33V is what I said. A 3.3Volt regulator.
    Left pin is ground. Center is Vout. Right is Vin.
    Presumably the 7805 5 volt regulator feeds it 5 volts to Vin.
    Remove the IC & check (on the board) between the Vout & ground.
    What is the resistance?
    If it is high, like 2K, you "may" be o/k.
    If it is low, like a few 10's of ohms or zero, you shorted something else out.
    You have to understand without a schematic we are all shooting in the dark.

  16. #16
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    yea. i think that would help me understand better too. i cant find a schematic anywhere.

    so is that -3.3 or +3.3?

  17. #17
    Supporting Member Jazz P Bass's Avatar
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    LD33V

    LD33V is a positive 3.3V regulator
    Power33LD33V \ Learning \ Wiring ALPHA 1.0

  18. #18
    Noodle of Reality Steve Conner's Avatar
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    The 3.3V is probably to run the big custom chip that does the whammying. An IC designed for 3.3V will not like having 9V shoved up it at all.

    Still, the troubleshooting approach is to get another LD33V and replace the one in there. If the pedal starts working again, great. If not, you've most likely blown the custom chip and turned your pedal into a doorstop: you can't buy a replacement as far as I know.

    There is a third possibility, maybe some little 5V rated bypass capacitor in there shorted out, and gave its life to save the IC. Or, maybe there are several ICs running off the 3.3V rail, and the one that blew is a non-custom part that you can replace.

    But according to Murphy's law, I'd suspect the main chip first.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    yea. i am gonna just get the part and see if it works.
    very expensive lesson if not.
    oh well.

    i have looked all over for the diagram and its not to be found.

    from what i can make out of the tiny and confusing circuit board, the out from the regulator has 3 big caps to ground before it gets anywhere then the power splits to several places on the same chip. some via a surface mount cap or resistor, other points go direct in.

    just fingers crossed i guess
    thanks for your help guys

  20. #20
    Supporting Member Jazz P Bass's Avatar
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    New Part

    I would check the resistance (on the PCB with the bad IC removed) from the Middle leg, Vout, to the Left leg, Ground, before I put a new IC in.
    High resistance is good. Low resistance is bad.(relatively)
    No sense ruining it further.

  21. #21
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    ok, i just did that.
    looks like it might be worse going on what you advised
    there is only a 2.2r resistance.

    i have taken a picture to try and make it a little clearer but i dont think i will ever get a schem for it. dont think it will be that much help tho my camera doesnt seem to do well with stuff that small.
    <br><p>

    http://i109.photobucket.com/albums/n76/kepeb/wham2.jpg

  22. #22
    Supporting Member Jazz P Bass's Avatar
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    3.3V buss

    You could try to trace out the 3.3V buss.
    At each connection to an IC, lightly cut the copper trace at that part.
    When the 2 ohm resistance bounces up to something realistic, you have found the toasted IC.(s)
    I see surface mount parts. If any are ASIC's(application specific IC) you will not be able to find them "off the shelf".
    Sounds like a doorstop.
    TIE (technician induced error) Ain't it fun.

  23. #23
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    well i dont think i'm confident i could cut the tiny traces or put them back accurately afterwards.

    what is the possibility that it will work with the new regulator before i try cutting traces etc? before i took the dead ic out that 3.3v buss was only getting 0.5v.

    you mentioned earlier about causing more damage by installing it.. how would that work?

  24. #24
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    also. before i removed the ic, some things i'm not sure i was clear on earlier which may give more indications...

    when i initially turned the pedal on the Led's flashed briefly, they're supposed to stay lit when the pedal 'boots' but they didnt do that anymore, they did still flash tho. is that a good or bad sign?

    when i hooked it up i still got clean signal going through the pedal... i just wasnt able to adjust anything because the led selector section was off. is indicative in any way?

  25. #25
    Supporting Member Jazz P Bass's Avatar
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    Shorted 3.3V buss

    I do not have the unit in front of me.
    My experience tells me that the 3.3V buss, shorted to ground (2 ohms from ground) is not good. A new IC will pop.
    Pack it in. It's dead.

  26. #26
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    ah ok, cheers man. that makes sense

  27. #27
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    ah ok, cheers man. that makes sense

  28. #28
    Old Timer J M Fahey's Avatar
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    Hi Kepeb, answer it yourself:
    Multimeter on 20VDC scale, black probe to chassis or known ground, red probe successively tests all 3 regulator pins . If any measurement is positive, it supplies +3.3V (or at least it tries to) ; if any voltage is negative , it supplies -3.3V.
    Post what you measure.

  29. #29
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    what?

  30. #30
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    i'm not quite sure where your going with that. or what i'm answering? i thought i had the answer.

    if i understand what your asking for...
    the regulator is a positive 3.3v regulator which has +9v on the input +0.5 to +0.9 on the output.

    the out is shorted to ground somewhere possibly through an ic which is powered from the +3.3v buss.

    as i dont want to risk further damage or 'TIE's' i wont attempt the micro surgery required to locate the exact fault. i'll leave that to someone else.

    i figured i am better off to just get another one.

    unless you have other ideas? i would be interested.

  31. #31
    Old Timer J M Fahey's Avatar
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    Hi Kepeb.
    I was giving you a generic (no-schematic no-datasheet available) test to answer your:
    so is that -3.3 or +3.3?
    question.
    While I had the page open, you received other answers, good.
    Sorry your pedal seems to have given up the ghost.
    Unfortunately, I guess not even the makers will repair it, being cheaper and safer just to swap boards or even give you a new unit.
    It's a pity that the warranty is over.
    Better luck the next time.

  32. #32
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    yea, tell me about it
    still.... you can but learn.
    i'll get a new one and NOT screw it up this time.
    thanks mate

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