Pioneer SX-950 wont come out of protection

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

  1. CavScout

    CavScout Active Member

    Messages:
    474
    I tested the voltages on the newly installed transistor and they are normal.
    Not sure what to do next
     

     

    Please register to disable this ad.

  2. Watthour

    Watthour Electron Rancher - JS3600

    Check the voltages of the power supply board (AWM-062) against the voltages indicated on the schematic. If they are all within 10% of the normal voltages the amplifier stages will need to be checked next.
     
  3. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    159
    Location:
    Mamou, Louisiana
    On the power amplifier board, Vr1, Vr2, Vr3 and Vr4. Need to check them. Vr4 may have opened up. See if indeed it did.Then replace all 4 of them, even if they check good, they can't be trusted anymore. Also check the power transistors and see if any are shorted. Easiest way for you would be to unplug the unit, put your DMM to ohms, and check the four .5 ohm 5 Watt emitter resistors and verify they are good. Then, on each channel, place 1 meter lead on each of the power transistor collectors and place your other meter lead on pins 10 and or 11 on one channel and pins 25 and or 26 on the other channel. If the meter reads low resistance, they are toast! Tell us what the reading are in ohms.
     
    Last edited: Jul 10, 2018
  4. CavScout

    CavScout Active Member

    Messages:
    474
    "Vr4 may have opened up"

    What does that mean ?
    Like physically popped open ?
     
  5. CavScout

    CavScout Active Member

    Messages:
    474
    "On the power amplifier board, Vr1, Vr2, Vr3 andVr4 Need to checkthem"

    What does it mean to CHECK THEM ?

    Thanks
     
  6. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    159
    Location:
    Mamou, Louisiana
    Open, meaning went way up in value. Instead of Vr4 being 100 ohms as it should be, it went wayyyyy up like thousands of ohms, or infinity which means open completely.
    CHECK THEM, means check them with your multi meter set to ohms. Check that Vr4 reads less than 100 ohms. Do the same with all of the pots. There are two 100 ohm pots, Vr3 and Vr4 and two 10,000 ohm pots, Vr1 and Vr2.
     
    Last edited: Jul 10, 2018

     

    Please register to disable this ad.

  7. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    26,241
    Location:
    uk.. the middle bit
    this is why i said monitor the bias and dont adjust yet and just do the offsets .. wont be anything that cant be fixed . it will just end up being netter all round now anyway .
     
  8. CavScout

    CavScout Active Member

    Messages:
    474
    Took readings on the 4 vr pots.

    My DMM was showing K ohms

    VR1 was 1.467
    VR2 was 3.317
    VR3 was not reading , just O.L
    VR4 was 0

    Not sure what to do now.
    Any suggestions?
    Hoping I don't have to replace as I am not sure where I would get them
     
  9. 1MEGΩ

    1MEGΩ Active Member

    Messages:
    159
    Location:
    Mamou, Louisiana
    Double check Vr3 and make sure it is in fact open. You will have to replace the pots if Vr3 is open. I would change them all anyway. Also check the power out transistors as described in my post above.
     
  10. CavScout

    CavScout Active Member

    Messages:
    474
    I checked vr3 again and it is still reading O.L.

    You referred to 4 large white resistors. Assuming these are the rectangular ones.......they are 8 of them (?)
     
  11. Watthour

    Watthour Electron Rancher - JS3600

    VR3 has become open. All four should be replaced. Further, once all damage has been assessed, there are some other items which should be replaced since you will be in there with a hot iron anyway. There is no need to power the unit on again for testing, since it will risk further damage. Check the resistance of the 0.5Ω ceramic/cement resistors (the white ones) along with the 150Ω ½W resistors R35-37 and the 4.7Ω 1W resistors R43-49. Remove the output transistors one at a time and test them using the 6-way resistance check. Test transistors Q9-11 in circuit the same way.
     

     

    Please register to disable this ad.

  12. CavScout

    CavScout Active Member

    Messages:
    474
    I pulled the heat sink away to remove the shield for better access to the board.
    Took new readings on the trim pots

    Vr1 8200 ohm
    Vr3 65 ohm
    Vr2 9900 ohm
    Vr4 83 ohm

    Went to the local electronics store and they only had these square blue trim pots. Didn't buy them... are they sufficient or do I need OEM style?

    Checked all 8 rectangular white noble resistors (.5 ohm 5 watt)
    All within 10% of spec

    Checked r37 thru r40......
    All within 10% of spec

    Checked r43 thru r5p.......
    All within 10% of spec

    Next step is

    "Remove the output transistors one at a time and test them using the 6-way resistance check. Test transistors Q9-11 in circuit the same way"

    Nervous about this as I have heard you can really screw things up if you mess up your output transistors.
    ALSO I have never done a 6 way resistance check
     
  13. CavScout

    CavScout Active Member

    Messages:
    474
    Do I even need to remove the output transistors? The back where the wires go in is marked which is which (see photo)
     

    Attached Files:

  14. Watthour

    Watthour Electron Rancher - JS3600

    The resistance tests are performed with power off. The ohmmeter will not likely have anywhere near enough current or voltage to damage any transistors in your set, unless you have one of these for testing resistance:

    [​IMG].
     
  15. CavScout

    CavScout Active Member

    Messages:
    474
    Just not sure where to put pos and neg . What is a 6 way resistance test ?
     
  16. Watthour

    Watthour Electron Rancher - JS3600

     

     

    Please register to disable this ad.

  17. CavScout

    CavScout Active Member

    Messages:
    474
    Thanks but can you clarify "forward and reverse directions?

    Basically what lead goes where and what readings am I looking for?
    I cant find this info in the manual
     
  18. CavScout

    CavScout Active Member

    Messages:
    474
    Please see my drawing, is that what 6 way means ?
     

    Attached Files:

  19. Watthour

    Watthour Electron Rancher - JS3600

    This is a representation of a basic bipolar transistor:

    [​IMG]


    This is the equivalent circuit diagram:

    [​IMG]



    All three P-N junctions need to be tested in both directions to read forward voltage drop and determine if each junction is intact.
     
  20. Watthour

    Watthour Electron Rancher - JS3600

    Your diagram is correct.
     

Share This Page