Spec 2 Errorr...

Discussion in 'Pioneer Audio' started by EchoWars, Sep 5, 2015.

  1. EchoWars

    EchoWars Hiding in Honduras

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    Dunno why I never noticed this before...

    [​IMG]

    Errors like this are common...usually either the foil pattern in the service manual or the schematic is wrong, but the silkscreen on the actual PC board is generally OK. But you can see that the positive lead of C4 must be tied to ground in order to avoid reverse-biasing the cap.

    Had a Spec 2 here that had been 'rebuilt', but as the protection let go and the bias interrupt relay closed, the relays would all open and close again very quickly, making a hell of a racket. Looking at the board, I could see that the last guy had replaced C4 with a 10µf 100V cap (which was bulged and swollen), perhaps in an effort to cure the issue. I hung the meter at the junction of R7 and R8 and measured -7V. Not good. Then I could see that the cap was installed just like the foil diagram in the manual, and the silkscreen on the PC board also is wrong, prompting the cap to be installed with the negative lead tied to ground.

    Popped the boards out, swapped the two C4's out with new caps, installed so that the positive lead is now going to ground (reversed from what the PC board shows), and now have -27V at the junction of R7 and R8.

    Needless to say, this cured the slap-happy relays. So if you're working on a Spec 2, check this. This specific unit looks to be an early one, and since it was partially recapped before I got it on the bench, I can't say if the original cap was installed properly oriented or not, but I can't imagine that Pioneer got it wrong regardless of the PC board marking.
     
  2. WhiteSE

    WhiteSE Is Lute Gluten Free?? Subscriber

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    Dang, that is what I call paying attention!!
     
  3. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    I just got to checking the one Spec II I completed and found I hadn't used good tech skills and installed it backwards.

    Thanks for the heads up!
    And yea, it's looking puffy! Hardly an hour on it.
     
  4. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    I add some images:

    Thanks "EW" for the post!!!

    I wanted to add that I didn't notice any chattering but this was the first Spec I had worked on and there is alot going on in there.

    Below is the correct orientation.

    [​IMG]

    A shot of the backwards cap after removal.

    [​IMG]
     

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    Last edited: Sep 6, 2015
  5. tsd71

    tsd71 RIP Tom Petty Subscriber

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    A gusher..almost.
     
  6. petehall347

    petehall347 the brandy coffee man

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    well spotted ..this is the reason i change one at a time or mark the board ..
    but if someone has been in there before it can get hard work .
     
  7. EchoWars

    EchoWars Hiding in Honduras

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    Hell, no cap at all would be better than the reversed cap. Glad you caught that one Zeb.
     
  8. WE6C

    WE6C Active Member

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    I will now be more aware. Thanks for the heads up.
    Bob
     
  9. EchoWars

    EchoWars Hiding in Honduras

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    Yeah, it wants to spew, but with that 33,000 ohm resistor there limiting the current to a trickle it can't muster enough energy to do so.
     
  10. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    I received a Spec II a few weeks back with one channel out. It was railed with a +56v's (DBT) on the speaker amp board pin 19.
    It had the original components installed and looked like it's never seen the techs bench.
    I wanted share what I found.

    All the E-caps are installed with the cap negative to the board negative.
    Both boards where identical. The scat for the unit includes the board mounted ceramic C6 and R51 1.3K components situated between Q2 and Q3's collectors.
    Both boards on this unit showed signs of overheating at Q6 an Q7, to where the solder melted and left no connection to the traces on the one channel. 100 ohm R11 was open and 100 ohm R12 was in the K ohm range.
    Once I replaced the resistors and shored up the solder connections, it fired up and showed a 25mv DC Balance and 20mv idle (DBT).
    I'm going to finish up the restore on both amps and will fire it up tomorrow.


    DSC04230.JPG

    DSC04233.JPG
     

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    Last edited: Sep 10, 2017
    slimecity likes this.
  11. slipstream55

    slipstream55 Active Member

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    This thread concerns me now. I looked at both of my Output boards and they sure don't look like zebulon1s post#4 photo. I have included a photo of my board.

    C4 1.jpg
     
  12. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    What you have is the same as the current one I'm working.
    Yours looks ok as the caps are not swollen. No worries if yours is operating.
    I would like to get to the bottom of the discrepancy.
    There are several different boards so:
    I'm still working through it.
     
  13. zebulon1

    zebulon1 Cleaned up the shop and half finished sets. Subscriber

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    I finished the restore on both boards and operated the set in both the original configuration and in the EW configuration and left it in the EW post configuration.
    Amps are set with no adverse issues.
     

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