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Thread: PB12 problem

  1. #1
    Senior Member Donald's Avatar
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    PB12 problem

    I have had the motorboating problem mention in the service bulletin supplied by someone here.

    What is the brown stuff at the base of the caps and around the transformer? It appears to have oozed from somewhere. In the photo called resist, check the flying resistor with the silicon blob above R42. Bad/burnt joint. And check the solder joints on the amp. Looks like it was done by hand, not automation. Very dirty.

    Could the brown junk have come from the caps? Check other messages for pics.
    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  2. #2
    Senior Member Donald's Avatar
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    amp
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    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  3. #3
    Senior Member Donald's Avatar
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    caps
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    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  4. #4
    Senior Member Donald's Avatar
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    resistor
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    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  5. #5
    Senior Member Donald's Avatar
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    transformer
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    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  6. #6
    Senior Member Don C's Avatar
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    The stuff around the solder joints on the board is just flux. Since I don't see so much flux elsewhere, I'd think that the board has already had that connection reworked once. It is considered good workmanship to clean off the flux with alcohol when finished soldering, but it is not uncommon to see it. I doubt if it is causing a problem, but I'd clean it off anyway.
    The other brown stuff looks like glue. Is the stuff solid, are the caps glued in place by it?

  7. #7
    Senior Member Donald's Avatar
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    The stuff could be glue. It is brittle. It is around the base of both caps. It looks like they stood the whole unit up before the glue set. It appears to have run down on the windings and base of the transformer. In the caps photo you can see it on top of some vertically mounted components labeled R10C.

    I plan to resolder the amp and I will clean off the flux.

    Not that it makes much difference but the black speaker wire was on the + post and the red on the -
    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  8. #8
    Senior Seņor boputnam's Avatar
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    Great reply, Don c...

    Now, about this...:
    Originally posted by Donald
    Not that it makes much difference but the black speaker wire was on the + post and the red on the -
    If you mean for the LF, that wouldn't necessarily be wrong.

    Lemme search for that schematic for the L222 network...

    *****

    I don't have it... Anybody?
    Last edited by boputnam; 04-25-2004 at 11:16 AM.
    bo

    "Indeed, not!!"

  9. #9
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    L222 or PB12?

    The PB12 information is too large to post and I wouldn't anyway.
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    Last edited by 4313B; 04-25-2004 at 11:40 AM.

  10. #10
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    L220A and L222A
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  11. #11
    Super Moderator Hofmannhp's Avatar
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    brown glue

    Originally posted by Donald
    ............I plan to resolder the amp and I will clean off the flux.
    .......
    Hi Donald,

    I wouldn't resolder the amp....the brown stuff is a special, well isolating, elastic (when fresh) glue for the mechanical reinforcement of the caps. It is often used for bigger parts to stabilize them on the PCB.
    It is also used for transformers to reduce their magnetostriction, which often produces hum and other noise.
    I recomend....close the amp, so you can't see it.

    HP
    Please help us save more info about the vintage systems. Let us register your speakers and drivers.

  12. #12
    Senior Seņor boputnam's Avatar
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    Re: brown glue

    Originally posted by Hofmannhp
    I recomend....close the amp, so you can't see it.


    And, thanks, Giskard! The library builds...

    But, Donald, I'm not more clear on

    "the black speaker wire was on the + post and the red on the - "

    comment. Can you elaborate, or are you going mad as a hatter from sniffing all that solder...
    bo

    "Indeed, not!!"

  13. #13
    Senior Member Donald's Avatar
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    The black wire from the speaker was connected to the spade lug on the PCB labeled + and the red wire from the speaker was connected to the spade lug on the PCB labeled -

    I plan to resolder the amp as that is the suggested fix to eliminate motorboating. Which this unit does even when there is no input signal.
    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

  14. #14
    Senior Member Don C's Avatar
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    It looks like they have made the board with two different sizes of spade lug so that the phase cannot be mixed up. I think that you have a phase switch on the back panel anyway.

  15. #15
    Senior Member Donald's Avatar
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    Don C,

    You are right. On reassembly I see the connectors are different widths.
    had L25,L36,L40,L120,L300,AquariusIV(2),S1,4408 have L65,L100,L222,DorianS12,B380

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