919

Discussion in 'Exclusively Sansui' started by Willy6, Aug 17, 2017.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    NO ! - copy the values in your unit now - don't use the parts list or the schematic. ;)

    It was tested at the factory with the values you have in there now, so unless you have a conflicting Sansui Service Advisory - follow the above advice - pretty please. :thumbsup:

    (Unless you have reason to believe someone has 'been in there' changing components for some nefarious purpose of course).
     
    Last edited: Oct 28, 2017
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  2. Willy6

    Willy6 AK Subscriber Subscriber

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  3. Willy6

    Willy6 AK Subscriber Subscriber

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    All of the resistors on F-2844 power supply board test good and pins 04 and 06 should have +40v and-40v so if it isn't the resistors dragging pin 04 down to +20v what else might be the culprit?
     
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  4. Willy6

    Willy6 AK Subscriber Subscriber

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    Don't worry I'm not messing with it right now I'm working 12 hour days the next 6 in a row so I have plenty of time to think over my next move my first day off is next friday..
     
  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    OK, I just thought there was a disaster about to happen. :)
     
  6. Willy6

    Willy6 AK Subscriber Subscriber

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    I couldn't sleep today and decided to pull F-2833 out and check everything over well I found that I was mistaken on the right side testing good and the left bad it appears to have a problem with both the left side and the right side vr05 right channel and vr06 left channel are controlling both the positive and negative voltages the positive side of the right channel reads neg 37mv and neg side of the right channel reads pos 10v and they read about the same on the the left channel..Vr03 right channel and vro4 left channel control nothing when trying to adjust them.. 20171101_194255.jpg
     
  7. Willy6

    Willy6 AK Subscriber Subscriber

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    Wierd
     
  8. Willy6

    Willy6 AK Subscriber Subscriber

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    I think I might have found the problem.I was studying lee stereos upgrade and restoration of a 919 thread and noticed that on his F-2833 board he had regular resistors in place of the voltage regulating trimmers vr03,vr04,vr05 & vr06 and I put the same bipolar caps in place of c03,c04,c05 & c06 as he did so I'm thinking I prabably need to switch those back to the polarized type to get the correct voltage adjustment..
     
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  9. Willy6

    Willy6 AK Subscriber Subscriber

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    Or try to figure out what size resistors go in place of the trimmers?
     
  10. Ronito6

    Ronito6 Super Member

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    OK...this an exciting moment.

    Hope this does the trick for you. Nothing like a moment of triumph!
     
  11. Ronito6

    Ronito6 Super Member

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    My best guess...

    Being careful not to change / turn the VRs upon removal, I would measure between the center leg and either the left or right leg to see what ohm the VR got set to when you set it, and then use a resistor of the value you find.

    Or just install a resistor that is half the ohms of the VR that was installed.

    Super-techs...what do you say??
     
    Last edited: Nov 3, 2017
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  12. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I don't think swapping the electrolytics will do anything useful, I would be looking at the transistors in the regulator section (on the MM head amp) first, also grounding on the MC head amp board, also ribbon cables - broken connections? - Plus the obvious - wrong value trimmers? and incorrectly installed components? - including the trimmers. :)

    Something very wrong if adjusting one trimmer moves two plus voltages or a plus and a minus :)

    Also you should be able to work on one channel at a time and get +/- 10V sorted on one channel before moving to the other.
     
  13. Willy6

    Willy6 AK Subscriber Subscriber

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    The tricky part is I'm only able to set the Neg 10v side of each channel with vr04 & vr05 the pos side vr03 & vr04 do absolutely nothing the way it is right now.Can't wait to get off work this morning and go find out the results..
     
  14. Willy6

    Willy6 AK Subscriber Subscriber

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    The transistors are all in right and are good the ribbon cables that go from F-2835 to the input terminal board F-2834 are diconnected from F-2835 at the moment,can't find any broken connections,trimmer values are right and installed the same way as the other ones that are working.I get off work in five hours and gonna try changing the electrolytics back to polarized first thing and if doesn't work it might be a jfet problem?
     
  15. Willy6

    Willy6 AK Subscriber Subscriber

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    Also on most of the 25 turn trimmers that I've had experience with I'm able to get both positive and negative voltage out of them..
     
  16. Willy6

    Willy6 AK Subscriber Subscriber

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    Ok John you can say I told ya so now:) Changing the electrolytics made no difference.I double checked the trimmer values at 50k ohms.How do you find a bad jfet?DBT shows no short circuit anywhere 150w light bulb gos completely out relays click amp powers up?Been a long night I'm going to sleepy land now.
     
  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    This is the bit of circuitry you need to look at - on the F-2835 MM Head Amp, note that the connections to VR03 & VR05 are through the ribbon cable. Leave the JFETs alone, they can look after themselves. ;)

    Note well that TR105 and TR101 (the top 2) are NPN, and that TR107 and TR103 (the bottom 2) are PNP - if you changed these transistors, check what you used. These transistors comprise a kind of regulator called a capacitance multiplier - you should have around +11V on pin107 and -11V on pin113, each adjustable with the respective trimmer.

    upload_2017-11-3_15-44-59.png
     
  18. Willy6

    Willy6 AK Subscriber Subscriber

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    Nope not that stuff already checked all of that over 3 or 4 times however I did find the problem on F-2844 power supply board TR05 is shorted on both sides.Anyone know what replaces this?
     
  19. Ronito6

    Ronito6 Super Member

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    What is the model number of that TR05?
     
  20. Willy6

    Willy6 AK Subscriber Subscriber

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    20171103_163317.jpg 20171103_163528.jpg
     

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