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Guidance on 9090db problem.

Discussion in 'Exclusively Sansui' started by imation_nation, Nov 4, 2018.

  1. imation_nation

    imation_nation New Member

    Messages:
    24
    Hi folks,
    I have a 9090db. I wish I would of just gotten the 9090, but I guess that’s another story.

    So, my problem. Basically, it works with these two issues. Regardless of whether I am using FM or using an aux input, the right channel sounds normal......... as long as the mono button is pushed in. If the mono button is not pushed in, I have no sound from the right channel.

    The other issue is the left channel. The left channel is just very subdued, kinda tinny, no matter what is selected.

    I was considering replacing all of the caps this winter. I don’t think that has anything to do with these two problems, but it seems like it is the prudent thing to do.

    Any help would be appreciated.

    Thanks.
     

     

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  2. danrclem

    danrclem AK Subscriber Subscriber

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    If you haven't cleaned all of the controls that would be the first thing to do.
     
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  3. avionic

    avionic " Black Knights " Subscriber

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    Yep.. Sounds like a switching issue.
     
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  4. LBPete

    LBPete Rolling Along Subscriber

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    Location:
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    This can happen on any integrated amp or receiver and is quite common on vintage equipment. The audio signal is dropping out in the preamp. This typically occurs as a result of dirty contacts in one or more of the controls. Each of the knobs and buttons on the front panel has a switch or a pot behind it. Almost any one of them can be causing this issue. As has been mentioned, cleaning the controls is the first step. On the 9090DB and most other TOTL models, it takes some disassembly to get access to these controls.

    Try "exercising" all the controls. Push all the buttons in and out, turn all the knobs and see if one or more brings some life to the dead channel.

    Also, please post the serial number for the database.

    - Pete
     
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  5. danrclem

    danrclem AK Subscriber Subscriber

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  6. imation_nation

    imation_nation New Member

    Messages:
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    I tried exercising the pots and switches, but this did not make any difference. I ordered a can of Deoxit and will report back after I have cleaned the pots and switches with it.

    Thanks all.
     
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  7. ManyMoonsAudio

    ManyMoonsAudio AKA paul79 Sponsor Subscriber

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    Since it is on and green means go, I am pointing blame at the preamp. Quick check of the amp is to plug another preamp into the main amp input on the back. If that is good, then you KNOW it is the preamp. A scope will allow you to see and trace the signal where it comes in to where it drops off. It might be in the dolby section or it might be the line stage.
     
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  8. LBPete

    LBPete Rolling Along Subscriber

    Messages:
    11,520
    Location:
    Long Beach, CA
    If you get sound from both channels when pushing the mono switch, the problem is definitely in the pre-amp at a point before the mono switch.

    - Pete
     
  9. imation_nation

    imation_nation New Member

    Messages:
    24
    I received the can of deoxit I ordered. I sprayed all of the switches and excercised each one. A lot. I counted to 50. I wasn’t sure exactly how to clean the push button switches. Didn’t really see a hole to spray in to. Did not resolve the problem. Here is a list of the problems I need to address in order of importance. Any guidance would be appreciated.

    1 Regardless of whether I am using the FM tuner or the aux port, the right channel sounds normal......... as long as the mono switch is pushed in. If the mono switch is not pushed in the right channel goes out although I did notice there is a very faint sound.
    The left channel is there although it is a little tinny sounding.

    2 There is one light out. I have ordered replacement led lights from David.

    3 I noticed that when I move the speaker wire a little bit on the left “A” side, it cuts in and out. I moved both speakers to the “B” speaker terminals and it doesn’t do this anymore.

    4 still want to replace some electrolytic caps and fuse resisters and those diodes.

    5 some minor cosmetic issues with the wood cover.

    I did remove the preamp to main amp connectors in the back and plugged in my iPhone using an adapter cord. The sound is very good that way so I guess the main amp portion is good.

    I checked the dc offset. With the speakers unplugged and the volume knob turned all the way off, the voltage was -10 on both channels.

    I went to check the bias, but it was zero, so I checked the meter and the fuse in it was blown so I will have to get a new one. I assume it was already blown.

    Pete, you mentioned it may be the preamp? Is that the driver board?

    Thanks in advance.
     
  10. avionic

    avionic " Black Knights " Subscriber

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    Always start out at the highest current range on your meter. Once you establish how much current is actually there, You can manually down range the meter for better accuracy. Don't want to ever ever over range- those fuses are pricey;)
     
  11. avionic

    avionic " Black Knights " Subscriber

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    No it is not. The driver board is the power amplifier section.
     

     

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  12. Trnsfmr_Jr

    Trnsfmr_Jr New Member

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    Unfortunately without a scope this problem is going to be slightly difficult to diagnose but you can still switch source wires to try to narrow it down. You could try switching the inputs to the dolby board. A blue and grey wire going into the bottom of the dolby board. If that doesn't switch the working channel you can be sure that it lies somewhere in the Dolby board or the push button board above it. Directly after that is the volume, then tone control board. Those must be working because your stereo works in mono. if it does switch the working channel you can be sure it drops signal before the dolby board. That would have to be the source selector board or an interconnect on the way. Hope this helps you. Good luck!
     
  13. imation_nation

    imation_nation New Member

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    24

    Good tip! I’ll keep that in mind the next time.
     
  14. imation_nation

    imation_nation New Member

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    Thanks for the idea. I think I will try this over the weekend.

    On a related note, I was lightly tapping the bottom of the Dolby board to see if the non working channel would pop in and discovered that when I was lightly, and I mean lightly pushing on the Dolby board, both channels would cut out. Unfortunately I can not narrow it down much. Seems to be a little bit more touchy past the ribbon connection away from the switch. Bad solder joint maybe. Adding that to my growing list of issues.

    One other question for anybody. Is it possible or a good idea to connect my iPhone output to the aux port to inject a tone into the system for troubleshooting purposes. I have an inductive wand at work that could possibly be used for signal tracking???

    Thanks.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    Hope its not a pass-through issue on the dolby board.
    Dolby board pass-thru's... AK search it..
     
  16. avionic

    avionic " Black Knights " Subscriber

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  17. avionic

    avionic " Black Knights " Subscriber

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  18. Blue Shadow

    Blue Shadow I gotta get me a new title

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    Be very careful if you think about adjusting the bias. The manual is wrong.

    I found that reading the voltage drop on one of the emitter resistors was so much easier and more straightforward that is how I did it. Kinda hard to get the mini-grabber clips in there but damn fine when they are connected. The exact measurement you are looking for in voltage drop is in a thread about the 9090db that I participated in.
     
  19. LBPete

    LBPete Rolling Along Subscriber

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    Location:
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    Just because you "cleaned it" doesn't mean it's clean. It is fairly difficult to clean the controls on a 9090DB, it takes a good deal of disassembly to get access. At the very least you have to remove the tuner tray to get access to the Dolby switch and related push switches. I'm guessing you didn't do that. Half measures won't fix it.

    These are typical symptoms of bad connections within the Pre amp. Almost any of the controls on the front panel can be the cause. As was stated in post #12 above, you need a 'scope to pinpoint it. Anything else is guessing.

    Spray some deoxit D5 on the speaker terminals. You are seeing the same type of poor connection that's happening in the Pre amp

    Don't even think about this until you get the other issues sorted out.

    If you were in doubt, this confirms the dropout is in the pre amp.

    Good, that's near perfect.

    Where did you put your meter leads to take that measurement?

    No, it's the main amp, as answered in an earlier post.

    - Pete
     
  20. imation_nation

    imation_nation New Member

    Messages:
    24

    Thanks for the heads up!!
     

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