sx 1250 Stabilizer voltage issue

Discussion in 'Pioneer Audio' started by sendust, Jul 3, 2018.

  1. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    Correction i reinstalled the board and now have 65vlt at 17 and ground but instead of -50 i have 2.7 vlt at 16 and ground not sure why this has changed from -50 vlt?
     

     

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  2. kevzep

    kevzep Its all about the Music Subscriber

    I think this is happening to help us find the problem.
    Okay thats better, Pin #13 and test point 16 are one and the same. The voltage should be the same there.

    If you have pulled the connector out a bit, maybe slip it back in and measure test point 16 WRT ground, just for shits and giggles.

    Check your D3 24 volt zener for correct polarity......

    Check D4 1n4148 for correct polarity.

    Then, pull C04 out, its a small ceramic 82P capacitor, you could lift one leg if its easier, then turn it on again and measure test point 16 WRT ground.
     
  3. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    I found d 3 was shorted, i replaced no change, both polarity correct, removed one pin on c04 retested no change 2.6-2.8 vlts
     
  4. sendust

    sendust Music feeds the soul Subscriber

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    716
    Can the issue arise from another board? i checked all resistors and diodes all seem to be fine, there is no short with dwb .
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    How much did you replace on the board, was it exactly that list?
    I can't see how there is a positive voltage on the negative rail....

    The circuit is actually quite simple, there's not much to it. So I think the next process is to double check your work, make sure there are NPN transistors in the right place PNP in the right place, make sure you have the pinouts right and the transistors mounted in the board correctly.
    Then if you get that AWR106 overlay out, you need to start testing the voltages around that negative circuit noting down the voltages and comparing them to whats on the schematic.
    I think you might have something incorrectly mounted, and trust me its easy to do....

    So have a look at those things and note down the voltages you have compared to what they should be so we can see where its getting pulled down...
     
  6. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    You were correct a transistor was improperly installed, i replaced it with a new one, checked all transistors and all are correct, now since board recapped and diodes etc i now have -45 at 16 using a cool amp, i am not sure if it will increase after running for a while. should i try this?
     

     

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  7. sendust

    sendust Music feeds the soul Subscriber

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    716
    I also should have mentioned this earlier, when i received the unit i had and still have an issue with the right channel on phono, not on any other setting, im not sure if that issue can affect stabilizer but i notice the boards do connect.
     
  8. kevzep

    kevzep Its all about the Music Subscriber

    Okay, thats good progress, I shouldn't think the phono amp would cause something like that unless it was a major power supply related issue.

    So -45 is as much as it will adjust? You can't get any more out of it?

    So test point 16 is at -45V, what I am interested in is Pin #14 which is the -25V supply. One can affect the other, so if we get a reading from that, this would be useful.

    The next process would be to find where the voltage is being pulled down, whether its the pass transistor or somewhere else...
    ECB readings around Q5, 6 and 7.

    This is where hanging that board out of the unit is useful, then you can get to everything to measure whilst its running.

    I like to print out the schematic and use a highlighter to mark down the voltages i have measured and put them next to the voltages in the diagram.
     
  9. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    -16.4 at 14
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    Okay looks like its being pulled down at Q5.
    Things that can affect this are the 24V Zener, which is replaced, D4 which is replaced, and finally, C04. Now I still suspect this, so now you have that transistor correct and we are back to where we started, lets eliminate this and pull it again.
    Only other culprits are the surrounding electro caps, which have been replaced.
     
  11. sendust

    sendust Music feeds the soul Subscriber

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    716
    Should i pull it and test without transistor?
     

     

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  12. kevzep

    kevzep Its all about the Music Subscriber

    Just take C04 out and turn it back on and check the voltage on 16.
     
  13. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    Took out one pin of c4, no change in voltage
     
  14. kevzep

    kevzep Its all about the Music Subscriber

    Okay, well we are going to have to go in deeper, let me have a look and come up with some ideas....
    I am in the middle of my work day right now...so it might be a few hours before I can take a break from the current task I am on...
     
  15. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    Thank you for all of your help.
     
  16. sendust

    sendust Music feeds the soul Subscriber

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    716
    Just to confirm all testing for voltages are done with no load on speakers, all selections off, jumpers removed and 5.1 resistors connected to power in
     

     

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  17. kevzep

    kevzep Its all about the Music Subscriber

    You don't need the resistors and the jumpers removed, it wont make any difference to these readings...
    Just make sure its not on the phono or tuner inputs, leave it on AUX and the volume down.

    I am beginning to think something post this supply is pulling it down.

    Now, in order to test this theory, you need to pull one of those connectors off. You need to pull the 5 way connector which is pins #11,12,13,14,15. its on the end. BUT and this is very important.
    You need to get an insulated alligator clip lead or a mini-grabber cable, and connect Pin #12 to GROUND/Chassis, can be anywhere on the chassis, I think there is a ground terminal nearby, you'll see a bunch of black cables going to it.

    Then measure either the Test point #16, or on the AWR106 Pin #13 AND Pin #14.
    Report those voltages back.
     
  18. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
     
  19. kevzep

    kevzep Its all about the Music Subscriber

    We need to continue to sort the stabiliser issue out as this powers parts of the amplifier that can cause other issues.

    I would not at this point worry about anything else but getting the AWR106 working properly.

    So you need to go and work that last measurement task I set for you and report back. Its entirely possible that this will take is to a problem with one of the other boards.....

    One thing at a time.....
     
  20. sendust

    sendust Music feeds the soul Subscriber

    Messages:
    716
    I will get these voltages Thursday, i had to travel out of town for my work. thanks pete
     

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