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Pioneer SX-950 wont come out of protection

Discussion in 'Pioneer Audio' started by CavScout, Jul 2, 2018.

  1. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    need to figure out whats not working on the supply board .
    voltages at q1 q3 and q5 . 9 readings . base collector emitter .. black lead to chassis .
     

     

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  2. CavScout

    CavScout Well-Known Member

    Messages:
    578
    So I need to remove the transistors?
     
  3. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    no .. voltage readings with power on .
     
  4. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Ok, sorry but I dont know where to take those readings since the transistors are deep in the heat sink.
    Are you referring to the wires that lead to the transistors?
    If so , how can I tell which one is emitter/collector and base ?
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    datasheets tell you which is b c e . or its marked on the board .
     
  6. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    219
    Location:
    Mamou, Louisiana
    Look at the service manual, scroll through the pages and you will see a page with all the transistor pin outs labeled B C E
    In reply #57, the TO 220 transistor pins are numbered 1 2 3.....1 is the base, 2 is the collector and 3 is the emitter. Hope this helps
     
    Last edited: Jul 8, 2018

     

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  7. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Power supply pins
    DC Voltage.

    1. this is Ground
    2. 5.46
    3. 5.46
    4. 13.83
    5. 13.83
    6. 52.22
    7. 52.22
    8. -0.98
    9. -0.98
    10. -0.98
    11. -0.019
    12. this is ground
    13. -13.4
    14. -51.63
    15. -19.96
    16. -0.023
    17. -50.58
    18. 50.66
     
  8. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    219
    Location:
    Mamou, Louisiana
    Pin 6 and 7 have the correct voltage, so that eliminates Q1 and Q3. They are good. You need to check Q5 and Q7. That is where the problem is since there is no voltage on Pin 8, 9, 10 and 11. Pins 8, 9 and 10 should have 36.5 volts DC and Pin 11 should have 28 volts DC. The Emitter of Q5 connects to Pin 8, 9, and 10 and should have 36.5 volts DC. It's collector should have 41.7 volts DC and the base should have 37.3 volts DC. The Emitter of Q7 connects to Pin 11 and should have 28 volts DC. It's collector should have 35.2 volts DC and it's base should have 28.7 volts DC. The problem is probably Q5 because Q5 feeds voltage to Q7. It could be a bad resistor in that circuit as well. R6 should have 51.5 volts on one end and 41.7 volts on the other end which connects to the collector of Q5. Let me know what you find.
     
    Last edited: Jul 8, 2018
  9. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,063
    Location:
    uk.. the middle bit
    q1 q3 are fine .
    6. 52.22
    7. 52.22

    q5 is in trouble .
    voltages both ends of r6 r7 . dont worry which ends . it should be obvious to see it written down .
     
  10. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Can you please clarify where I should be looking for Q5 and Q7 ?
    Are they small transistors on the power amplifier or are you referring to the oval output transistors to the heat sink?
     
  11. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Thanks Pete but you are losing me LOL .
    What and where are R6 and R7 ?
    Resistors ? What board ?
    Test voltage or ohms or ?
     

     

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  12. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Here are some pics
     

    Attached Files:

  13. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Ok, so I think I found the R7.
    On the power supply board right ?

    If so what do I test for ? DC ?
     
  14. CavScout

    CavScout Well-Known Member

    Messages:
    578
    On the assumption of the readings are from the power supply board I read:

    R6 52v DC on both pins
    R7 52v DC on one pin and 38.2v DC on the pin near Q5
     
    Last edited: Jul 8, 2018
  15. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Readings on Q5

    Base 38.2v DC
    Emitter -0.975v DC
    Collector 52v DC
     
  16. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    219
    Location:
    Mamou, Louisiana
    This is on the power supply board. Do you have a schematic? I posted a link for you to get a service manual and a schematic. Did you open it?
     

     

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  17. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Hi Pete, I found it, see the info I posted above, thanks for the continued help. Hoping we are onto something
     
  18. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    219
    Location:
    Mamou, Louisiana
    Replace Q5. It is open on Base to Emitter.
     
  19. CavScout

    CavScout Well-Known Member

    Messages:
    578
    Ok, so just like for like ?
    Not sure if they have that part number in my local area (Calgary Alberta Canada)
     
  20. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    219
    Location:
    Mamou, Louisiana
    It is a 2SC1318 NPN transistor.
     

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