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Accidentally fed ipod into preout w/ jumpers in...no preamp now

Discussion in 'Exclusively Sansui' started by Linehand, Aug 6, 2018.

  1. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    So I have another thread going on this unit, but this issue is specific and separate.

    I repaired the driver board, re capped the power supply, and was setting bias on the right channel when I got called away (brand new little baby in the house).

    Came back and plugged my ipod into the PREOUT 1 with MAIN IN jumpers connected to PREOUT 2 instead of AUX by accident. Powered up, volume down, a couple seconds pass and I've got music left side only. Look at the board real quick and see that I left the right side (F04) fuse open (what an idiot). And why is there music when the volume is down? (double idiot!!)

    At this point I can't get music from a signal fed into the aux. I went to MAIN IN with the ipod and I do have sound both channels there, albeit with some low signal warble sound passing through even with volume at 0.

    I see the signal passes to F 2623 on the schematic but I can't find it and I'm not sure thats where I should be starting anyway.

    I was so close to being done and now back to square one. If anyone has dealt with this please let me know.

    Thanks
     

     

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  2. Silentnet

    Silentnet AK Subscriber Subscriber

    Messages:
    860
    Location:
    Charleston, SC
    Surprised the weak-a** iPod output could do any damage...

    Don't have much to add though. Hope others more electrically knowledgeable than myself will chime in. Good luck with it.
     
  3. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    I wouldn't think so either. What worries me is the seconds that passed before I had music. Makes me think the signal had to fight the path backwards through the PREOUT back to the MAIN IN. I hope I'm wrong.

    The tuning meter works and the Dolby/Power meters show movement when set on Dolby.

    What controls the amp signal back to those power meters?
     
  4. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    Anybody have a suggested starting point?

    I wish I had more time to research, any advice would be greatly appreciated.
     
  5. EngineerNate

    EngineerNate AK Subscriber Subscriber

    Messages:
    3,275
    Diode test the transistors (and any diodes along the way for good measure), working from the preouts back through the preamp board. I wouldn't be surprised if one or more has failed open on you.
     
    Linehand and slimecity like this.
  6. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    Thanks Nate
    I found the signal path flow through the various boards. Does anyone have test points for the AUX signal? How can I confirm signal is present on the different boards?
     

     

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  7. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,095
    Location:
    uk.. the middle bit
    you seem to have forgotten to mention what unit it is ?
     
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  8. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA

    Whoops that'd be helpful...

    9090db
     
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  9. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,095
    Location:
    uk.. the middle bit
    to blow fuse 4 it would take something like shorting the output . maybe a speaker wire shorted ? .. best test the even numbered outputs .
     
  10. avionic

    avionic " Black Knights " Subscriber

    Messages:
    44,597
    Location:
    Fort Dodge, Iowa
    He narrowed it down a bit..:biggrin:
     
  11. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    I have both channels when I bypass the preamp and go MAIN IN...

    Edit: I had Fuse 4 removed as I was measuring mA across that channel
     

     

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  12. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    Good eye!

    Do I need a scope to test the blue/gray for signal presence at the dolby board?
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,095
    Location:
    uk.. the middle bit
    pre out 1 and pre out 2 are one and the same .they connect together so rules out anything there .
     
  14. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,095
    Location:
    uk.. the middle bit
    i dont quite get this bit .. am puzzled as to why you want to connect main in to aux ?
     
  15. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    So the signal from my iPod (iphone actually) was fed into the preout with MAIN jumpers installed. No big deal I would think, however, I had music playing as if I was feeding direct to MAIN IN. That makes sense seeing as they are bridged.

    However, now I have no signal from AUX back to the PREOUT.

    I'm tracing out the AUX feed through F2653 to see if I can identify anything failed in the path. If theres a way to test for AUX signal presence at different positions, it would narrow my problem
     
  16. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    It was by mistake, I did not intend to feed a signal into the preout
     

     

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  17. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,095
    Location:
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    you could check voltages ic01 ic02
     
  18. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA

    I'm not sure where that is, you'll have to forgive me I'm learning as I go but a bigger picture is starting to emerge- its not a lost cause :confused:
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    28,095
    Location:
    uk.. the middle bit
    right there on F2653
    damp finger tip testing might be safer for now though so long as you dont go near the power supply .
    basically you follow signal path between the boards . if it makes a hum on the speaker everything forward of that point is passing a signal .
     
  20. Linehand

    Linehand AK Subscriber Subscriber

    Messages:
    104
    Location:
    Los Angeles, CA
    How do I rouse the Sansui Gurus? Anybody local here in SoCal? I got good beer and good tunes on deck... I know LBPete is from Long Beach haha
     

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