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

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

  1. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Idle current on one channel reads -001 no change when adjusting vr3.Currently in protection mode.DC bias adjusted to 0 on both channels.
     
    Last edited: Feb 9, 2019

     

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  2. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    DC bias is not a thing, idle current or bias is one thing, and DC offset is something else. You need to figure out why it is in protection. Where did you measure what you are trying to measure, and how? Did you acquire it dead or did it die while you were using it?
    And welcome to Audiokarma :)
     
  3. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

    Messages:
    5,056
    Location:
    Las Vegas Nevada
    The other channel is responding to the trimmers correctly? DC Balance (Offset) and Idle (Bias).
    The one bum channel adjusts for DC Balance but not Idle(?).
    And Yea Merlyn's questions.
     
  4. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    yes exactly.
     
  5. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    i bought in protection mode.Dc offset good on both channels idle current good on one channel.Measured from pins 2 and 6 on bad side 15 and 19 on good side.per service manual.
     
  6. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    o volts on dc offset on both channels 50 mv on right channel 0 on left channel for idle current
     

     

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  7. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Took readings on power amp pins 1=59.7
    2=40mv
    3=-59.4
    4=34mv
    5=0
    6=0
    7=-58.7
    8=0
    9=0
    10=63
    11=0
    12=0
    13=-58.7
    14=-58.7
    15=0
    16=0
    17=0
    18=-60
    19=60.8
    20=0
     
  8. zebulon1

    zebulon1 Building a new bench. Finally! Subscriber

    Messages:
    5,056
    Location:
    Las Vegas Nevada
    I think a good visual check of both sides of the amp board. The board is split down the middle so check the bum side with a good LED flash light an magnifier.
    Look for poor solder connections and toasted components.
    The resistors sleeved in fiberglass sheath are highly suspect. Check them against the good channels sister resistor for values.
    Look for broken wire wrap connections. Tug on the wrapped wire, making sure the wire is good and secure.
    I'll check your voltages tomorrow but the visual inspection is important.
    You'll have to dissemble to see the back of the amp board. Be careful and use sound electronic safety techniques.
    Never remove the wire wrap connections. Loosen the harness from is plastic keepers too gain access.
     
  9. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Will do.Thank you.
     
  10. Watthour

    Watthour Electron Rancher - JS3600

    Something is keeping the right channel in protect, probably related to the 60V measurement on Pin 19. It could be an output transistor (Q24/26)shorted E-C, and thus it may help to test those. The Molex connector can be unplugged to isolate the transistors for testing without removing them.

    If the transistors test good, in addition to the suggestions above, it may be helpful to check the bias circuit in the right channel. Carefully note the position of VR4 (a photo is always good reference). With power off, measure the resistance from end to end on VR4 and note that as well. Then adjust the pot slowly from end to end, monitoring for any point where the resistance changes drastically, or goes open-circuit. Exercise the trim pot several times from end to end to help clean the wiper and trace, and assure contact. Return the pot to the originally noted position. Check the resistance in the left (working) channel as a comparison. expect a small difference, but not a major one.
     
  11. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Will do.Thank you
     

     

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  12. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Checked output transistors on amp no shorts.Tested vr4 and vr3 both go from zero to 4.4 k smoothly.
     
  13. Watthour

    Watthour Electron Rancher - JS3600

    It may also be helpful to check all of the SVT-3s on a diode test for continuity and voltage drop.
     
  14. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Will do .Thank you.This project is keeping my mind off some medical problems.All of your help is so kind.Great
     
  15. Watthour

    Watthour Electron Rancher - JS3600

    Well, focus is good, but sometimes distraction can be beneficial to sanity.
     
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  16. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    778
    Location:
    High Plains, Eastern Colorado
    Please post the Protection Ass'y AWM-090 pins' voltages also . . .
     

     

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  17. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    1)0
    2)-12.6
    3)7.43ac
    4)27mv
    5)-37mv
    6)30mv
    7)37mv
    8)-30mv
    9)0mv
    10)0
    11)33mv
    1262.5v`
     
  18. Watthour

    Watthour Electron Rancher - JS3600

    The differential from Pin 6 to 7 (Left channel) is a mere 7mV. The differential from 4 to 5 is almost 65mV, which is coincidentally about the correct voltage to forward bias a semiconductor junction.
     
  19. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Any idea what i should test next?
     
  20. kubotadave

    kubotadave New Member

    Messages:
    43
    Location:
    watertown ny
    Checked the board over good.Found no burnt components,no broken wires,traces looked good.Tested the resistors and they were same value as right channel.soft start relay clicks,but speaker protect relay still not closing.Any help will be greatly appreciated.I can take any readings and report back when finished
     

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