SX 780 and intermittent operation

Discussion in 'Pioneer Audio' started by Chevelle70, Feb 25, 2019.

  1. Watthour

    Watthour Electron Rancher - JS3600

    Desolder each pad one at a time, then use a solder aid of some sort to push the power pack lead away from the pad. Move on to the next, etc. A pencil can make for a good solder tool if you don't have a dedicated one - Lead solder will not stick to the carbon of the pencil. When you're done the pack can be removed for some testing, and the excess solder on the circuit board can be removed with copper wick, a solder sucker, or whatever method is most convenient.
     

     

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  2. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    932
    Location:
    High Plains, Eastern Colorado
    Looks to me like the left pack is toast. If you have (or can get) a couple of 1kΩ resistors, you can solder them in where the STK was and it will help the troubleshooting process. On the PCB, after the pack is removed, connect one from pin 0 to pin 8, one from pin 1 to pin 3. See pictures:
    Pioneer SX-780 red dc-test.jpg z-adamson.jpg
    This closes the DC feedback loop to see if the rest of the power amp section is ok or not.
     
  3. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    Ok thanks for all the info! I’ll dive into this Sunday and report back. I guess if I’m going to learn it might as well be now!
     
  4. Chevelle70

    Chevelle70 New Member

    Messages:
    42

    I should do this even if I have sound coming from the other side? This still tests the left side amp section only? Thanks
     
  5. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    22,413
    Location:
    Glen Burnie Md.
    Correct. Left side only. Leave the Right side alone for now.
     
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  6. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    Ok I was able to get the left channel pack out- relatively easy. What do I test now?
     

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  7. Watthour

    Watthour Electron Rancher - JS3600

    Perform a resistance test oft the module. Measure (both polarities/directions) between pins 2-3, pins 8-9, and pins 1-0.
     
  8. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    932
    Location:
    High Plains, Eastern Colorado
    After the STK resistance test results,
    Verify the 0.22 Ω resistors are good.
    Solder the 1kΩ resistors to the PCB between pin locations 0 and 8, & pin locations 1 and 3 like in the pictures in post #22.
    Power up on DBT and measure dc volts from ground (chassis) to PCB pins:
    1)
    2)
    3)

    8)
    9)
    0)
    2 and 9 are power supply - and +, may be a bit low while on DBT.
    0 and 1 are module inputs, 0 should be a few volts positive ~3 to 5 vdc, 1 about the same voltage negative, exact value not critical, but balanced around 0 vdc.
    3 and 8 are module outputs, should be close to 0 vdc, 3 slightly negative, 8 slightly positive, just a few millivolts.
    Don't bother to test for sound, none will come from side with resistors instead of STK.
    If these are close then the power amp input section (before STK) is likely in good condition.

    EDIT: more info
     
    Last edited: Mar 15, 2019
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  9. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    2-3 showed 1 (which must mean open?) both directions

    8-9 showed same as above

    1-0 showed 11.27 (red on pin 1)
    1-0 showed 1 (open?) black on pin 1
     
  10. merlynski

    merlynski Curmudgeon Electronicist Subscriber

    Messages:
    932
    Location:
    High Plains, Eastern Colorado
    Did you measure 1 ohm between 2-3 and 8-9? If so the STK is shorted, a usual failure mode for overloaded STKs. Or was it a 1 at the left side of the meter display, which would mean 'open'? Neither is a good reading.
     
  11. Watthour

    Watthour Electron Rancher - JS3600

    Thus far, presuming that the meter reading was 1___ or OL and not 1.000, the module may be viable.

    Also measure between 1-2 and 1-3, then 0-9 and 0-8. 1-2 should show a junction drop, just as 0-9. 1-3 and 0-8 should show very high resistance or open.
     

     

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  12. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    22,413
    Location:
    Glen Burnie Md.
    Turn on your meter to resistance and hold your probes apart. Note the reading (open) which may be a blank, 1 or O/L (out of limits). Now touch and hold the probes together. You'll note that there is usually some resistance (under 1Ω). This is your baseline resistance for the probes, and should be added to your readings of other components, especially those under 1Ω (finally got it!) for components like emitter resistors and such.
     
  13. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    Exactly this - when the probes were not touched together it showed a 1 on left side of meter, same result when I touched them to 2-3 and 8-9. I assume something happened inside the pack and the path is damaged causing a open circuit?

    Sorry this is quite new territory for me but everyone’s help is greatly appreciated!
     
  14. Watthour

    Watthour Electron Rancher - JS3600

    So, if the 1___ display is open circuit (like the older Fluke 8000 series) your readings are as expected.

    1-0 should show the junction drop in one direction only, or about 1.2-1.4, and no reading in the opposite direction.

    2-3 and 8-9 should show no reading.

    1-2 and 0-9 should show the junction drop in one direction only.

    Of course, depending upon the meter and what voltage it applies for the diode test function (and it varies greatly) the readings may be different.

    The most important thing is that of the junctions which are measurable from the external pins, none are showing a short.
     
  15. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    1-0 readings measured both directions
     

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  16. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    Forgot these:

    1-2 read 9.75 one direction and 1 . On opposite

    0-9 read 11.47 one direction and 1 . On opposite
     

     

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  17. Chevelle70

    Chevelle70 New Member

    Messages:
    42

    Thanks - open circuit reads 1 .

    Touching together reads 0.00
     
  18. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    1-2 shows 9.75
    1-3 showed varying voltage for a second then goes open ie: 12.40 for 1 second then 1 .

    0-9 shows 11.47
    0-8 shows 1 .
     
  19. Watthour

    Watthour Electron Rancher - JS3600

    It sounds as if your meter has resistance ranges but no diode check function, commonly indicated by a symbol like this -►|- which on some meters is integrated into a 2KΩ scale, other on a 200Ω scale, and yet others a dedicated scale.

    If the meter is not testing in diode check mode, the readings are in ohms (Ω) and will be a little less definitive. Still, the most important thing is that none of them appear to be shorted (0Ω). Also, if the meter is used in an auto-range mode it is important to note whether the indication is in Ω, KΩ, MΩ, or otherwise. 9.75KΩ at a junction would be just great, but 9.75Ω would be a disaster.
     
  20. Chevelle70

    Chevelle70 New Member

    Messages:
    42
    I do have that setting on my meter - i remeasured and came up with:

    1-0 1423 (shows open reversing leads)
    1-2 1105 shows open reversing leads)
    1-3 shows voltage then goes open - open when I reverse leads
    0-9 1186 (shows open when reversing leads)
    0-8 shows voltage then open-reversing leads just shows open
     

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