Sansui 881 - Recapping (I'm going to do it!)

Discussion in 'Exclusively Sansui' started by Blistex, May 5, 2012.

  1. BrianPH

    BrianPH New Member

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    I finished recapping my 881's power board, tone board and driver board. The unit powers up without issue however, sadly, there is no audio output from any input/speaker output combination. Perhaps I soldered a component in with the polarity reversed, lifted a trace or have a cold solder joint. Are there any obvious places to start looking or does anybody have any troubleshooting suggestions?? Can the audio signal be traced with a probe to find out where it dies??? Are there any common mistakes that people make when recapping when it comes to reassembly are connecting wires?

    I hope I didn't just spend all this time for nothing. Thanks for any advice

    Brian
     
    Last edited: Dec 23, 2014

     

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  2. BrianPH

    BrianPH New Member

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    Also, C04 on the power board (1000uF 50v) had three contact points. The electrolytic that replaced it had only two. Should there be a jumper between the (-) terminal and the unused ground plane point?
     
  3. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    The third thru hole I believe was a second ground really there for stability in soldering the cap in. You can always run a jumper on the board if your worried about it but your probably fine.

    As for not getting any audio from either channel, is your speaker protection relay closing? The click you hear a few seconds after startup is the relay on the power supply/protection board. If offset is high it will not close to protect your speakers.
     
  4. pete_mac

    pete_mac Super Member

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    The third point is to provide physical stability to the original capacitor. If the replacement cap lacks the third pin, then there is no need to install a jumper as this will serve no electrical purpose.
     
  5. BrianPH

    BrianPH New Member

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    I'm not sure about the relay closing. I do hear clicking sounds at power on. Is there a way to verify proper function with a multi-meter?
     
  6. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    Power the unit up and you can visually see the relay close. You could also run a test signal into the unit and check for vAC on each side of the relay. Even easier with a scope. If you look at the bottom of the relay there might be four wires going to the terminals. That is the incoming L and R channel and the output from the relay.
     

     

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  7. BrianPH

    BrianPH New Member

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    OK, when I power I can both hear and see the relay closing. Any other standard checks to make regarding no audio output?

    Thanks so much for your input guys, I really appreciate it. The receiver was working fine before re-capping so I imagine that it can't anything too complicated.
     
  8. BrianPH

    BrianPH New Member

    Messages:
    49
    There is one thing that I'm wondering about. During the recap, I lifted a trace around a component on the 2436 Driver board (which could totally be causing this issue, as all audio runs through this circuit...correct??). Trace lifted at (+) terminal of C12 which is connected by trace to four component leades.... center (collector?) terminal of TR04 transistor, Emitter terminal of TR06 transistor, R12 resistor, R08 resistor. From the component hole that had the lifted trace I simply wired all downstream connections point to point and confirmed continuity from the capacitor lead to these 4 connected points. That should be good enough to maintain the integrity and signal flow of the circuit, right?

    Here are pics of the board and the point-to-point repair.

    Driver board TOP post-re-cap:
    [​IMG]

    Driver board BOTTOM post re-cap
    [​IMG]

    Point to Point repair:
    [​IMG]
     
  9. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    ^ That looks fine. C12 is connected to the collector of TR04 which is half of the input differential pair. If there was an issue you would have high offset issues and the speaker protection relay would not close.

    Silly question but you have speaker A chosen from the selector switch on the front, right?
     
  10. BrianPH

    BrianPH New Member

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    Yes. The speaker outs are properly selected.
     
  11. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    Odd that it is both channels. Dirty tape monitor button maybe? Do you have a scope?
     

     

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  12. BrianPH

    BrianPH New Member

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    No audio regardless of source selection. Im not sure as to of what else to check
     
  13. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    Ok, try pressing the tape monitor button a few times and see if sound breaks through.

    If no difference, pull the pre out / main in jumpers on the back. Take a source with a volume control such as an mp3 player and plug it into the main in with the volume very low. Turn on the receiver and play music on the source, slowly raising the volume. Your effectively making the mp3 player the preamp. If you hear sound then you know the amp is not the problem.
     
  14. BrianPH

    BrianPH New Member

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    Hi Mike. Where exactly are these jumpers located??

    I'm beginning to wonder if I lifted a trace elsewhere and hadn't noticed it. What a bummer.
     
    Last edited: Dec 26, 2014
  15. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    The jumpers are located upper right corner of the inputs. It may be a heavy gauge piece of wire going from one RCA jack to the other.

    Go over the driver board and do continuity checks on all parts you replaced. It is just odd to have the amp come out of protection and make no sound out of both channels. Did you swap any other parts in the unit besides the driver board?
     
  16. BrianPH

    BrianPH New Member

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    Ok I'll check continuity on the driver board. I also recapped the power board, tone and EQ boards.
     

     

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  17. HVHiFI

    HVHiFI Hudson Valley HiFI Subscriber

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    You've got some homework to do. First you need to isolate the loss of signal to either the preamp (tone) or amp (driver). This is done by following my post above, pull the jumpers and see if signal passes through the amp and preamp separately. Several caps in the preamp are in the signal path and if backwards will cause a channel to drop out.
     
  18. BrianPH

    BrianPH New Member

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    I just checked continuity surrounding all replaced caps on Power, Tone, EQ and Driver boards. Also checked all component polarity. Still am uncertain about this "jumper". I see all sorts of wires connecting to the RCA input jacks.
     
    Last edited: Dec 27, 2014
  19. two.dogs

    two.dogs Active Member

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    The 881 doesn't have pre out / main in, so no jumpers.
     
  20. BrianPH

    BrianPH New Member

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    Fuses all test good. Checked diodes on PSU. Still no audible output from any input/source selection. Is there a way to confirm that ample power is reaching driver and tone boards? Any way to trace audio signal? I don't have a scope. Was able to dial in DC offset and bias for both channels. All pots and switches have seen De-Oxit. I feel as though it's something simple, like a connector wire, since all of a sudden no audio source input is passing but I'm kind of at my limit as far as troubleshooting goes. Does anybody know a reputable technician near the Austin TX area????
     
    Last edited: Dec 28, 2014

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