no change in one channel when adjusting idle current on pioneeer sx-1050

Discussion in 'Pioneer Audio' started by kubotadave, Feb 9, 2019.

  1. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    Protection Board voltages, second report . . .
    Those all look ok: pins 4 and 5 are right channel, difference of 84 mVdc (0.084 Vdc); pins 6 and 7 are left channel, difference of 5mVdc (0.005 Vdc)
    If the protection relay is not pulled in you may have two problems, the bias adjustment failure and a protection board fault.
    What are the dc voltages on the cathodes of D6, D7 and D8, and the emitter, base and collector of Q5 on the protection board?

    Sorry Watthour, but your decimal point is off, silicon pn junction is about 600mV to forward bias (0.600 vdc not 0.065 vdc) I know you know . . . :rolleyes:
     

     

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  2. Watthour

    Watthour Electron Rancher - JS3600

    DOH!

    But... But... It's JUST an order of magnitude.

    (Good catch.)
     
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  3. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    UPDATE: I just noticed that pin 11 is: 46 with no mV. Is this a typo and it is 46mV, or is it now actually 46 Vdc? On previous reported readings it was around 33mV. Also the power amp board pin 4 is 43mV, which is connected to Prot pin 11.
     
    Last edited: Feb 11, 2019
  4. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Yes it is 46mv.Sorry
     
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  5. kubotadave

    kubotadave New Member

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    43
    Location:
    watertown ny
    should readings be done with molex connectors unplugged?I took readings on all four transistors,and compared to good channel.The readings were different from 14 all the way to 20.unplugged molex connectors and took readings,and the values were close to good channel.could it be the output transistors are bad on the bum channel?What would be a good way to prove this?Thanks again for all your help.Im not fixing this to flip it.Im just trying to get back in to this as a hobby for retirement.
     
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  6. Watthour

    Watthour Electron Rancher - JS3600

    If both channels were tested in the same configuration (outputs connected) and the L channel showed differences, there may indeed be problems in the outputs.

    Instead of powering the unit on with the outputs disconnected, you could try to remove two of the outputs in the suspect channel, one NPN and one PNP, then test the voltages again. For example, you could unscrew and unplug Q24 and Q26, then test again.

    Keep in mind that the unit was purchased in "DOA" condition, and we have no idea what may have been done to it previously. It would be a really good time to verify that the correct output transistors are in the correct positions, just in case someone pulled them for testing some time in the past and may have mixed them up when reinstalling. It's just a possibility. You may also find that the outputs test a little differently when they are removed from the circuit.
     
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  7. kubotadave

    kubotadave New Member

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    Location:
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    Will do and report back
     
  8. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Took out q24 q26 plugged in molex connectors readings on collectors of q19 and 20 is the same now
     
  9. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    What are the dc voltages on the cathodes of D6, D7 and D8, and the emitter, base and collector of Q5 on the protection board?
     
  10. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    d6) 28v
    d7) 7v
    d8) 7.3v
    q5) e 8.21v
    b 7.79v
    c .63v
     
  11. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    The b-e junction of Q5 has 0.42 volts across it, so it should not be conducting, yet the collector is +0.63 v when it should be -1vdc, so it appears as if Q6 is on, keeping the protection relay off. The cathodes of D6 and D7 should be about equal, yet they are not, which means the Q3/Q4 diff amp is unbalanced, indicating a DC offset problem. However prot board pins 8 and 11 are very close to 0vdc, not enough dc to be an offset problem. Lift one end of D6, 7 and 8 and test them. Pull and test Q3, Q4 and Q5. While they are out power up (if safe to do so) and see if the prot relay pulls in. I suspect it will.
     

     

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  12. kubotadave

    kubotadave New Member

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    Location:
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    Will do after supper.Thank you
     
  13. kubotadave

    kubotadave New Member

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    Location:
    watertown ny
    QUOTE="kubotadave, post: 12451114, member: 281131"]Will do after supper.Thank yoYU
    You were absolutely correct!I have sound in right channel nothing on left.Still working on that problem
     
  14. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    Did you identify any failed components? All we have done is cut the heart out of the protection circuit, still have to figure out why it was triggered. Do you have replacements for Q3, 4 and 5? With the protection circuit disabled be very careful not to damage any other parts. If there is a DC offset failure it will fry your speakers. If you have a pair of cheap speakers you would not mind losing hook them up instead, otherwise disconnect your speakers.
     
  15. kubotadave

    kubotadave New Member

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    43
    Location:
    watertown ny
    I have replaced q7 q6 and all caps i think i will just replace all the other transistors
     
  16. kubotadave

    kubotadave New Member

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    Location:
    watertown ny
    The speakers are real cheapos i used to test with
     
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  17. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
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    Check at the cathode of D5 (zener) for ≈+33vdc when power is on.
    Good idea, did D6, 7 and 8 check ok?
     
  18. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    would you know the mouser part # for q1 thru q5 on the protection board,and the output transistors on amp?Sorry i am justing getting back in to this after being out for 30 years.Loving it though.
     
  19. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Not yet.Should i just replace them too?
     
  20. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    Here is a list of SX-1050 replacement parts I have been working on for a while. Original Credit goes to markthefixer and mattsd, as well as others. It was up-to-date as of a couple of weeks ago. Some parts (especially caps, film in place of electrolytics) have substituted items from suggestion of others here on AK. The original spreadsheet had too many columns to stuff in one pdf, but the original pcb and part designations are on the left, Mouser subs are on the right. You should check them yourself before/as you order. I have an SX-1050 I bought new I am working up the list for a comprehensive repair and refurbishment.
    The main power supply filter caps are a 50% increase in capacitance but should still fit the original clamps (I think)
     

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    Last edited: Feb 12, 2019

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