New AU-9500, 1st problem

Discussion in 'Exclusively Sansui' started by awise1961, Oct 4, 2010.

  1. awise1961

    awise1961 Super Member

    Messages:
    2,525
    Location:
    Nashua, NH.
    The honeymoon is over.
    My new to me AU-9500 has developed its first problem.
    Last night after being enamoured by this units sound and power all weekend, it started having as terrible staticy, crackling sound coming from the left channel. This sound started every so slowly and I initially thought it was a bad album track, but alas it progressed. It is independent of the volume level. Turning the volume all the way down does nothing to subside it. As is with all of the other switches and and functions. The only thing to stop the sound is to turn off the unit. I performed the usual process of eliminations by plugging in the right speaker into the left and so on, and also trying another pair of speakers. The problem stays with what ever is connected to the left channel. I also tried "Speakers B" and Speakers C" and it persisted and only on the left channel. Next, I repmoved my turntable connections and the noise did not go away even though there was no source plugged in.
    It is my opinion that I have one, or more capacitors leaking AC voltage on the left channel driver board.
    Unfortunatley I am Logan airport as I write this on my way to LA. for business until late Wednsday and won't have a chance to play with it until Thursday. I downlaoded and printed out the service manual and I wil study on my flight shortly.
    If this is indeed the problem, I would like to order the CAPs for both the left and right boards and do a total replacement. I would like to order the components tonight from my hotel room so they can arrive at the end of this week. Any reccomdations and opinions are greatly appreciated. Especially if it is determined to be the CAPs, what brand, what values, and where should I purchase them?

    Thanks, Al. Wise
     
  2. Bob91343

    Bob91343 Super Member

    Messages:
    2,021
    My guess is that you are about to experience a major failure in the output stage. A transistor, I suspect, is beginning to flake and you may have disaster imminent.

    What to do? Well I would open the unit with a dummy load connected and probe with an insulated tool around the output amplifier to see if something is mechanically marginal. You may have a bad transistor or capacitor, more likely the former. A bad solder joint is possible also. But don't leave your speaker connected or you may damage it.
     
  3. motorstereo

    motorstereo the wonder of it all Subscriber

    Messages:
    9,858
    Location:
    Connecticut
    I had the exact same problem with my 9500 about a year ago. I took it to my tech and he had it fixed quickly as it was only a couple of small items he replaced. It's been playing without a hiccup ever since.
    RodG6000's 9500 has also recently developed the same problem. Normally I keep all my repair receipts but somehow this particular one has turned up missing. Too bad as my tech lists the part numbers that he replaces. I took the top off my unit hoping to spot his work but darned if I could see the new parts. If it's any consolation it's not a terribly expensive fix. Good luck to you in getting it up and running soon.
     
  4. Zekeman

    Zekeman AK Subscriber Subscriber

    Messages:
    2,253
    Location:
    Chicago
    I believe that old germanium diodes (I think) can cause static. They are VD1212-type diodes in some other similar-vintage Sansui models. The 9500 probably has some on driver boards.
     
  5. afZal

    afZal Member

    Messages:
    60
    i had this problem before with the same sansui au-9500.. if i were you, better replace all this diodes in both channel.
     
  6. EchoWars

    EchoWars Hiding in Honduras

    Messages:
    28,946
    Location:
    Kansas City
    The VD1212 diodes are NOT germanium. They are a multijunction silicone diode.

    On the 9500, you have the capability to separate the amp from the preamp. Do it, and observe the results regarding the noise. If it is in the amp section, it is most likely one of the differential pair transistors. Match a new pair and put 'em in.
     
    Willy6 and slimecity like this.
  7. awise1961

    awise1961 Super Member

    Messages:
    2,525
    Location:
    Nashua, NH.
    Thanks.
    When I get home from my trip I will seperate the amp and preamp sections and see what the outcome is.
    Also, I want to swap the driver boards from left to right and see if the problem follows accordingly.

    If I hadn't mentioned it earlier, the volume level from the left channel is no weaker than that of the right, and the music playing through it is clear. The noise (static like crackling) seems to be overwritten on top of the music and this noise varies up and down in its own volume level while the music volume remains constant.

    What "TR" designation are the differnetial pair transistors and are they on the driver board, or somewhere else?
    Also, where should these be sourced (Digikey?) and what part number would be good to use?

    Thanks, Al. Wise
     
  8. EchoWars

    EchoWars Hiding in Honduras

    Messages:
    28,946
    Location:
    Kansas City
    The E-copy of the manual I have is too crummy to read part designations on. Google 'differential pair transistors', or post a scan of the amp section.

    The 9500 uses PNP input pairs. The Fairchild KSA992F would do well here.
     
  9. OverLoad

    OverLoad High On Solder Fumes

    Messages:
    1,385
    Location:
    Ontario, Canada
    On the driver board F-2029 the differential pair transistors are TR801&803.
     
  10. awise1961

    awise1961 Super Member

    Messages:
    2,525
    Location:
    Nashua, NH.
    Thanks, I'm putting together my shopping list as I sit here at my hotel tonight.
    Regarding the capacitors, I was in a FRY'S Electronics to kill time here in LA. this afternoon and they had the values of capacitors that I need. Although I didn't buy any, it made me wonder about whether I should use polarized, or non polorazed capacitors. Does it matter?

    Thanks, Al. Wise
     
  11. mroboto

    mroboto Super Member

    Messages:
    1,257
    Last edited: Oct 5, 2010
  12. awise1961

    awise1961 Super Member

    Messages:
    2,525
    Location:
    Nashua, NH.
    Thank you!


    Would you eplace all capacitors, or just the electrolytics on the driver boards, all electrolytics, or all caps.? Also, with all of us replacing components shouldn't we put together a master component cross reference for these replacements?
    A lot of the various cap's, resistors, diodes, and trannies are carry overs from Sansui to Sansui. It would be great to have sticky of a spread sheet with the cross references from old to current part numbers that we can update. I know that if it would help me and possibly help many others as well.
    Pleae excuse me if it is already available and I can't find it.


    Al. Wise


    Al. Wise
     
  13. mroboto

    mroboto Super Member

    Messages:
    1,257
    Depends of the condition.

    I have changed nothing in my AU-9500 and i like the sound.

    If i change electrolytics on this one,i would think about changing progressivly.

    I don't want to change everything and afterward, don't recognise it anymore.

    If you change every electrolytics,keep the old ones in case of regrets.

    Electrolytycs may be the only ones that needs to be refreshed.

    Nichicon for the big ones, Elna Cerafine and Elna Silmic II , Nichicon Muse BP or Elna BP (Bipolars) ...
     
    Last edited: Oct 5, 2010
  14. AwdeeO

    AwdeeO New Member

    Messages:
    26
    Any owner should keep an eye on R847 on the prestage boards - the plug in boards shielded right next to the heat sinks of the finals. Sansui wired a 330 ohm resistor in series with a thermal fuse that is attached to a transistor with a copper clamp. I have found the copper clamp and chrome fuse connection points corroding in these units. The reaction will cause an open - the fuse does not blow and rather the corrosion eats away causing the fuse to become open. Just a quick visual is all that's needed, look for green or a gunky build up at this point. I'd replace it and discard the thermal fuse with a Thermal resistor or none at all - you be your own best judge but I have not felt this transistor get hot and found it overkill. If it opens the relay will not kick in. Is it a source for distortion and interference? Any time you have contamination on a board or near a circuit component - you very definitely have the potential
     
  15. nosirrah

    nosirrah Moderator Moderator

    Messages:
    7,756
    Location:
    30 min north of seattle
    Have you seen this condition on more than one unit?:scratch2:
     
  16. JoshHendi

    JoshHendi vintage audio student Subscriber

    Messages:
    905
    Location:
    southeastern Washington State
    Reviving this old thread, I have my 9500 opened up and checked my boards and am getting some pretty major corrosion. My unit isn't showing any of the OPs issues, but would like to pro-activly take care of this... Could I just remove the fuse and small heatsync connecting to the transistor and just install a standard 330 ohm resistor in the R847 spot?
     

    Attached Files:

  17. Leestereo

    Leestereo Super Member

    Messages:
    1,915
    Location:
    Ottawa, ON
    No problem doing such, you can also reuse the resistor that is already there.
    Dirver Board Original.jpg AU-9500 Driver Board.jpg

    Pictures from Restoration/Upgrade Of Scribby31's Sansui AU-9500
     
  18. JoshHendi

    JoshHendi vintage audio student Subscriber

    Messages:
    905
    Location:
    southeastern Washington State
  19. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    10,934
    Location:
    Long Beach, CA
    Please post the serial number for the database. Click on the link in my signature block.

    - Pete
     

Share This Page