Crown CE1000A amp with some shorted output transistors

Discussion in 'General Electronics Chat' started by henlopen, Nov 9, 2015.

  1. henlopen

    Thread Starter New Member

    Nov 9, 2015
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    I'm working on my first Crown 1000A that came in dead with 4 output transistors bad, Q128,214,223 and 227. Also found Q210, 211, 220 and 231 Triac also bad. Scores of SMD Resistors were open as well, R400,401,402,405,406,407,408,411,412 and R250,R265, R252,253,256,257,259,267,268,271 and 272. After replacing the above parts and finding no other abnormalities, I replaced the circuit board and when power was applied with no load, proceeded to blow open all the above resistors except for R400 and R259. This time, I again found Q231 shorted, Q214 leaky, Q210 leaky, and Q227 shorted. Everything else I've checked tests good including Q221 and 212. It's nice to have two separate channels to compare readings to if one is presumed to be good. Q232 checks the same as Q132 but I'm wondering if I should change it also. Any ideas?
    Thanks,
     
  2. bertus

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    Apr 5, 2008
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  3. henlopen

    Thread Starter New Member

    Nov 9, 2015
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    I read the entire thread, and was amazed with the detail you went into. Matter of fact, I went through all three threads that I could find looking for clues before posting my query. I kinda suspect that only someone who's repaired quite a few of these may be able to help me at this stage, although I'm still hopeful that a light bulb might go off from someone reading the list of parts I've found bad. The Amp was given to my son in laws church not working, and I don't know the operating environment it was used in. While still trying to fix it, I realize that "no good deed goes unpunished." I plan to order the parts that I've found bad so far, and give it one more try though. Thanks,
     
  4. bertus

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    Hello,

    You say that Q128 also is faulty.
    That would mean that 1 transistor in the first channel is also faulty, as the others are in the second channel.
    Is the 128 a typo?
    I can not find Q231, Q232 and Q132 you mention in the schematic.

    You can download a service manual here:
    http://www.crownaudio.com/media/pdf/legacy/130352-1_10-02_ce1-2_serv_revd.pdf
    (It is not the best quality, I must say).

    Bertus
     
  5. henlopen

    Thread Starter New Member

    Nov 9, 2015
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    That is correct. Q128 measured different from the others, and figuring it might short out in the near future, I replaced it out of an abundance of caution. Not knowing the history of this rig, I was trying to be through. It looks like I'm going from the same service manual that you have, and I'm using schematic 127451-4 almost to the end of the manual. Q231 is the Triac MAC9D and Q232 is an MBS4993 Triac driver SBS. Since the Triac is shorted, perhaps I should order and replace the driver as well? Q131 was on a different schematic (102141), so you can disregard that. Thanks for the reply. I'm in Delaware btw.
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The triac and diac are shown in the revision D schematic:

    henlopen_ce1000_triac_diac.png

    The circuit will short the output when there is a big DC on the output.
    This is likely done to avoid plopping of the speakers.

    The circuit is not on the revision B schematics that I have.

    Bertus
     
  7. henlopen

    Thread Starter New Member

    Nov 9, 2015
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    Then it looks like in this unit, each time the triac shorts the output when enough DC is sensed, it stays shorted and must be replaced. I haven't been able to find any other components bad to cause this problem, so will go ahead and reorder the Triac and SMD .39 ohm current sensing resistors, and give it another try. Will try powering it up via a variac next time while checking for current draw.

    Bill
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have taken the endstage from the schematic and marked the parts you mentioned to be defective:

    henlopen_ce1000_endstage.png

    I would also check the driver transistors Q212 and Q221.
    Also the end stage transistors Q215, Q218 and Q219 in the upperpart and Q224 and Q228 in the lower part of the schematic.
    As the resistors on those transistors are blown, they must have given a large current blast.

    Bertus
     
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