Sansui Six issue

Discussion in 'Exclusively Sansui' started by Cary Joe, Jun 14, 2018.

  1. Cary Joe

    Cary Joe New Member

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    I've got a Sansui Six that only works in mono. The outputs seem to be working, that is the levels from both sides seem level in mono, anyway. I've got a manual and diagrams, but I need suggestions as to where to start.
     

     

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  2. Celt

    Celt Peanut Head Staff Member Super Mod

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    Does it have a "mono" switch....and is it depressed in?
     
  3. Cary Joe

    Cary Joe New Member

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    I've tried it pressed and release. In mono, i get both outputs (mono) but in stereo, just one channel.
     
  4. Tom B

    Tom B AK Subscriber Subscriber

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    Exercise the other switches as well. Tape monitor, function switches, and any other push button or rotary switch. Switches can get dirty causing problems as this.
    After trying all switches identify the following

    Does this problem appear in all functions?? Phone, tape, FM, AM, AUX etc??
    Does the FM Stereo light come on??
     
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  5. Cary Joe

    Cary Joe New Member

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    I get the stereo light, and it looks like the tuner, phono, and accessory inputs do the same regarding the mono-stereo problem. As far as I can tell, when the switch is depressed, you get mono, which I do, from both channels. They're even in outputs, left and right.
     
  6. jberger

    jberger AK Subscriber Subscriber

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    Since you get sound from both speakers when you feed the same signal to both channels with the MONO button, we can assume both channels of the power amp section work.

    Since this happens with all sources, we can also assume that this problem is not in the tuner section.

    See how simple that was? With a couple of questions, we eliminated 2/3 of the receiver as possible problem areas.

    That leaves the control amp (or preamp) functions of the receiver.

    Since you lose one channel when NOT in mono, but get output when IN mono, the problem exists in the circuit before things connect through the mono switch. Since this affects all channels, it's after the point where one source is selected (input selector) and passed on.

    Now, follow Tom B's advice, and work those switches, especially the tape monitor and external processor loops (give them a round of twenty or more cycles, repeatedly); see if it changes anything. If it improves, you've probably bought time, but will need to get some contact cleaner inside the suspect switch.
     

     

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  7. shelly_d

    shelly_d Not An Audiophool

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    The input selector can still be the culprit and needs to be worked as well. The output of the selector might not be making good contact.
     
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  8. Tom B

    Tom B AK Subscriber Subscriber

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    There are 5 switches before the mono switch that can be the culprit.
    Switch 1 main selector switch
    Switch 2 noise reduction adaptor
    Switch 3 tape monitor 1
    Switch 4 tape monitor 2
    Switch 5 (4 channel adapter)
    Switch 6 mono/stereo switch

    Turn the balance control to the channel that doesn't play in stereo, cutting off the good side, leaving the volume at a normal level

    Slowly exercise all the switches 1 at a time. If you hear sound momentarily when you exercise a switch, that one needs cleaning, although I would say probably all need cleaning. Highly suspect are the tape monitor switches and 4 channel adapter switch. You already know that the mono switch will bring in the silent channel but check to see if you get sound momentarily as you just start to depress the switch, but not going all the way into mono.
     
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  9. Cary Joe

    Cary Joe New Member

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    I spent a little time cleaning the pots and switches. In FM stereo, the only audio i get from both sides is a bit of bleed-over from the other side at higher volume. In AM, I get both sides, but if course, that's a monk signal. Checking the phone inputs and auxiliary input, I now get stereo output from them. Looks like the problem is now in the multiplex calculator circuit somewhere. Progress!!
     
  10. Tom B

    Tom B AK Subscriber Subscriber

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    So its just FM stereo single channel problem. It could still be a dirty function switch but may be component related.

    My experience points to a bad cap or coil
    C419 or L407 if the problem is the right side
    C420 or L408 if the problem is on the left side

    Easiest way to see if this is the issue is to get a small 1uf capacitor and jump across the capacitor connection (observe polarity) If this doesn't bring it back, then use the 1uf cap to jump across the 2 active pins for the coil as seen on page 30 of the SM. Active pins are left 2 pins for L407 and right 2 pins for L408. Using this cap will couple the signal across the coil if it is bad.

    If this doesn't show the problem, you may have a bad 10k ohm resistor (r437 right or r438 left)
    Very slim possibility of T403 right, or T404 left being bad

    But I would suggest you get a can of deoxit and clean all the switches first, before parts swapping
     
    Last edited: Jun 15, 2018
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  11. Cary Joe

    Cary Joe New Member

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    I'm using LPS Electro 140 contact cleaner/lube. Is detox any better or cheaper? Since we lost Radio Shack, that looked to be about as good as any. A little pricey, but that's how it goes. I'll check those components this afternoon and let you know how it goes.
     

     

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  12. smurfer77

    smurfer77 AK Subscriber Subscriber

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  13. Tom B

    Tom B AK Subscriber Subscriber

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    I would be careful as that stuff may be harmful to plastics. You want to use something that is safe of plastic because the internals of many of the switches contains plastics.
    Caig deoxit D100 is great for switches and Caig fader lube is great on rotary controls like volume, tone, and balance controls.
     
  14. Cary Joe

    Cary Joe New Member

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    I thought I might have a 1uF cap, but the closest I've got are some 47's and some 0.47's (electrolytic) that I can parallel. Close enough? I'm a luthier, and haven't done any board work in 15 years. Lots of non-electrolytics for electric guitar work, though.
     
  15. Tom B

    Tom B AK Subscriber Subscriber

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    0.47 would be fine
     
  16. Cary Joe

    Cary Joe New Member

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    I've learned that the LPS works fine, as long as you don't "drown" components in it. Years ago, I overused a lot of tuner cleaner (mostly Radio Shack) to make for faster cleaning. Older and hopefully a bit wiser, Guitar tube amp guys like the LPS better, but they don't do the same kind of board work as you. On a Bakelite tube socket, for example, the LPS is great for cleaning pin contacts, but a newer plastic socket would show the solvent damage. Looking at the specs, the detox looks like great stuff, and I'll get some right away. Thanks!!
     

     

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