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

  1. #21
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments
    Got the parts last weekend and during the week replaced the burnt resistors and blown out C3L & C3R. Returned to it this afternoon and installed Q1, Q2 and (shot) diode D80.

    Did not order replacements at the time but I just now checked D3R & D20. D20 measured .546 but D3R was .356. Should not that be minimum .500?

    If D3R has been damaged, can I use an IN4005 instead of an IN4004? Just asking because I have on hand a couple of the former.

  2. #22
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    Halfbiass...Electron Herder and Backass Woof
    .356 could be influences from other parts of the circuit. The only way to know for sure is to desolder one end...
    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 "

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    "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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  3. #23
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments
    Done. But still the same reading.

    1N4005 is a no go? If so, I can get 1N4004's tomorrow - the local shows them on hand.

  4. #24
    Administrator Gepetto's Avatar
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    Quote Originally Posted by 62vauxhall View Post
    Got the parts last weekend and during the week replaced the burnt resistors and blown out C3L & C3R. Returned to it this afternoon and installed Q1, Q2 and (shot) diode D80.

    Did not order replacements at the time but I just now checked D3R & D20. D20 measured .546 but D3R was .356. Should not that be minimum .500?

    If D3R has been damaged, can I use an IN4005 instead of an IN4004? Just asking because I have on hand a couple of the former.
    Yes, 1N4005 is just a higher voltage rating version of a 1N4004

  5. #25
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    Halfbiass...Electron Herder and Backass Woof
    Gary. I don't know what the difference is between a 4 and a 5 , I suspect it's a voltage rating...
    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 "

    " I Just Collect Smiles Craig......Cheap Smiles!-----Fishoz-2017

    "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

  6. #26
    Administrator Gepetto's Avatar
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    Quote Originally Posted by laatsch55 View Post
    Gary. I don't know what the difference is between a 4 and a 5 , I suspect it's a voltage rating...
    4005 = 600V
    4004 = 400V

  7. #27
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    Halfbiass...Electron Herder and Backass Woof
    Thanks Sir Joe!!
    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 "

    " I Just Collect Smiles Craig......Cheap Smiles!-----Fishoz-2017

    "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

  8. #28
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments
    Yes, my thanks as well.

    I went ahead with using a 1N4005 once Joe OK'd it and replaced both voltage regulators as well. So the new parts are:

    R72R, R73L, R73R, R34L -because they were burnt
    D3R - because of low reading
    D80 - because it was bad
    Q2 & Q1
    VR1 & VR2
    C3L & C3R - because they blew open

    Once done, I brought the amp up to power with a variac and DBT and at full voltage, the DBT had a dim glow. Plugged in a discman, increased it's volume slowly and the amp played - for about a minute. Then DBT brightened so I shut 'er down.

    After a 5 or so minute wait, I started increasing voltage on the variac. I thought it strange but the at little power, the discman, still connected, was being amplified enough to be clearly heard through the speakers. Once I had the AC power up to full, the DBT stayed dim.

    Not being sure what to do next, I checked DC offset (without discman or speakers connected) which was about 12mv each side and bias current that was about 41mv. Have not yet adjusted that as I thought to learn what the hiccup was that that brightened the DBT.

    The above took about 10 minutes and I left the amp powered up during the process. No change to DBT - just a dim glow at full power.

    Anyone have any suggestions - voltage checks, shorts or....?

    EDIT: Would incorrectly connecting the bias transistors cause that anomaly? I ask because I obtained them from Glen - a couple of "Lee's Specials" and I think Glen may may have connected them differently. I now have them connected as per the photograph provided by Joe.

    Click image for larger version. 

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    Last edited by 62vauxhall; 06-18-2017 at 11:07 PM.

  9. #29
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    Halfbiass...Electron Herder and Backass Woof
    Cold solder joint maybe??
    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 "

    " I Just Collect Smiles Craig......Cheap Smiles!-----Fishoz-2017

    "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

  10. #30
    Forum Veteran 62vauxhall's Avatar
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    No such things as bad days, just bad moments
    I don't think so. But your suggestion made me push on all the parts I replace and no change to the DBT.

    However, I used the discman again, watching the DBT as it played. Please note that I have the discman plugged directly into the 400 and am using its volume control. So this might be a fundamental case of cause and effect but if the signal increases in amplitude, maybe it was a "dynamic" on the first CD I played or in this "just now" instance of increasing the volume, the DBT got brighter. Is this to be expected as the amp is under load?

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