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Thread: PL20 REV C board capacitors C3L & C3E went POOF

  1. #1
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments

    PL20 REV C board capacitors C3L & C3E went POOF

    I thought I'd be buttoning up the amp tonight.

    The unused board was mounted, connected and worked in this 400 amplifier about a month ago. The face plate has been off and meters disconnected ever since awaiting the install of a new light board which I did today. Ironically, I just bought a variac and this was the first time I used it. Part of the delay was waiting for the arrival of some white LED's to replace the blue ones which I received yesterday.

    All went well, the variac brought the amp up to power and the LED's illuminated. Before putting on the face plate but after attaching the meters, I thought to re-check the bias once again. The amp was powered up for 30 or so minutes then turned off as I connected the DMM for left channel bias check which was a bit low so I adjusted to 350mv. Turned the amp off again, attached DMM for right channel bias check, turned up the variac and as I waited for the reading to stabilize, heard a noise and witnessed a fair bit of vapor being released. The tops of C3L & C3E had opened and vented.

    I assume that replacing those two capacitors is not the answer unto itself. Anyone know what may have gone wrong?

  2. #2
    Administrator Gepetto's Avatar
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    Quote Originally Posted by 62vauxhall View Post
    I thought I'd be buttoning up the amp tonight.

    The unused board was mounted, connected and worked in this 400 amplifier about a month ago. The face plate has been off and meters disconnected ever since awaiting the install of a new light board which I did today. Ironically, I just bought a variac and this was the first time I used it. Part of the delay was waiting for the arrival of some white LED's to replace the blue ones which I received yesterday.

    All went well, the variac brought the amp up to power and the LED's illuminated. Before putting on the face plate but after attaching the meters, I thought to re-check the bias once again. The amp was powered up for 30 or so minutes then turned off as I connected the DMM for left channel bias check which was a bit low so I adjusted to 350mv. Turned the amp off again, attached DMM for right channel bias check, turned up the variac and as I waited for the reading to stabilize, heard a noise and witnessed a fair bit of vapor being released. The tops of C3L & C3E had opened and vented.

    I assume that replacing those two capacitors is not the answer unto itself. Anyone know what may have gone wrong?
    Yes that means your +20V regulator is not working.

  3. #3
    Administrator jbeckva's Avatar
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    Errm... Ey Vatos!!!!
    Quote Originally Posted by Gepetto View Post
    Yes that means your +20V regulator is not working.
    Think it went from 20 to 85 volts?? Yikes that's not good...
    Mains - WOPL'd 400 Backplaned With Fully Complementary Output Stage / Sansui AU-517 (Pre Only) / CV D-9's (mod'd)
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  4. #4
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments
    I'm using my phone trying to locate that +20 volt regulator and have not found anything to identify it. Any chance of getting a part and location number?

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    Halfbiass...Electron Herder and Backass Woof
    They are the TO-220's in the middle of the board, mirroring each other..along with the TL-431 --TO-92's....also in the middle of the board....
    taking something that's already good, and making it better...........and for the knowing smiles that cross their faces.......Nando-2011...

    "Silence cannot be Misquoted"--Lazarus Short-2012 "

    "Keep it Simple so It's Simple to Keep" Stephen Evans--2013 " Don't trust a man who will not listen to music, for he doesn't trust his own emotions"

    "anything can be done, it's finding the easiest way that's hard"-----Bobbysdad--2014

    " Synth percussion is deadly to children, house pets and shitty power supplies"---Stephen Evans 2014

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  6. #6
    Administrator Gepetto's Avatar
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    Quote Originally Posted by 62vauxhall View Post
    I'm using my phone trying to locate that +20 volt regulator and have not found anything to identify it. Any chance of getting a part and location number?
    Emailed you docs Gary...

  7. #7
    Forum Veteran WOPL Sniffer's Avatar
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    Screw it
    I am NOT saying that this is what happened, just saying I have seen this before (Premature Failure of Components), or, it could have been a shitty part. I try to make sure it's not ME, when building boards (I have screwed up though). As I had a discussion before, try to use some form of heat sinking boys and girls. You can't do squat about crappy parts, but you can try to minimize the effects of the soldering iron. HEAT KILLS




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    I had the nations problems figured out one night while on acid in the 1970's. I wrote it down an a "Big Bamboo" rolling paper and you know what happened after that............ I'm too old to do any more acid so yer stuck with the shit mister.

    Big amps
    Kenner Close N Play

  8. #8
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments
    Thanks G, thanks L. When I thought to check voltage to the new LED board, a (-) meter terminal got away from me. In addition to hitting and "interrupting" a trace on the LED board, now fixed, I suspected it might have whacked somewhere on the main board as I thought I heard something at the time. I guess that is what happened. Serves me right for not taping off those terminals and I had no real reason to check that voltage in the first place, just got curious. Wish I'd had that variac a day or two sooner.

  9. #9
    Forum Veteran WOPL Sniffer's Avatar
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    Screw it
    ouch
    I had the nations problems figured out one night while on acid in the 1970's. I wrote it down an a "Big Bamboo" rolling paper and you know what happened after that............ I'm too old to do any more acid so yer stuck with the shit mister.

    Big amps
    Kenner Close N Play

  10. #10
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    Halfbiass...Electron Herder and Backass Woof
    Quote Originally Posted by 62vauxhall View Post
    Thanks G, thanks L. When I thought to check voltage to the new LED board, a (-) meter terminal got away from me. In addition to hitting and "interrupting" a trace on the LED board, now fixed, I suspected it might have whacked somewhere on the main board as I thought I heard something at the time. I guess that is what happened. Serves me right for not taping off those terminals and I had no real reason to check that voltage in the first place, just got curious. Wish I'd had that variac a day or two sooner.
    Always learnin...
    taking something that's already good, and making it better...........and for the knowing smiles that cross their faces.......Nando-2011...

    "Silence cannot be Misquoted"--Lazarus Short-2012 "

    "Keep it Simple so It's Simple to Keep" Stephen Evans--2013 " Don't trust a man who will not listen to music, for he doesn't trust his own emotions"

    "anything can be done, it's finding the easiest way that's hard"-----Bobbysdad--2014

    " Synth percussion is deadly to children, house pets and shitty power supplies"---Stephen Evans 2014

    " You have not reached the point of diminishing returns, you've just ran out of money

    " The Pioneer U-24, unfortunately, is just too expensive and rare to find. That's why I have one."--Nando-2014

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