Sansui AU-7700 Speaker pop when Relay clicks

Discussion in 'Exclusively Sansui' started by micaiahm, Jul 9, 2017.

  1. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Speaker pop when relay engages. The relay engages at about two seconds from turn on.

    Otherwise no issues. This thing sounds awesome with HPM-100s.

    The following work was performed based upon much reading on this forum. This is a fully recapped unit, all based upon what was original to unit. C23 is 470uf 6.3v based upon spec. All SA726 and SC1313 transistors have been replaced with ksa992 and ksc1845. Transistors 27, 29 and 31 in protection circuit have been replaced. TR27 had been previously replaced and the trace damaged, but this has been fixed and a new ksc2383 transistor installed. Relay has also been replaced because former was worn. DC and Bias have been checked and set.

    Any help is greatly appreciated...
     
  2. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    be certain c23 is correct way round .
    if it is you could try and give more delay by upping c23 value a bit . maybe a 560uf .
    2 seconds seems a short delay to me .
     
  3. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Thanks Pete for the reply. (I was thinking about using the sansui while I keep working on the pioneer)

    I pulled and checked the cap last night. It is installed based upon the markings on the board. I know there are mistakes sometimes, do you know if the board markings for C23 are correct?

    Two seconds seemed quick to me also but it was all to spec. I was wondering about upping the capacitance to increase the delay. Would the short delay be causing the speaker pop?

    Thanks
     
  4. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    yes it could cause a pop if the circuits are taking longer than 2 seconds to stabilise . i take it the vol is turned right down at power up ?
    negative side of the cap goes to ground . same as tr29 emitter

    also if d23 was leaky it might speed up the delay .
     
  5. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Yes, volume is at zero. Tone and filters are off.

    I will double checked the ground of C23 and it is on the same as the emitter of TR29.

    What is a good replacement for D23? I figure if I have to order a few things I might as well get as much as I can to save on shipping.

    Checked d23 out of circuit. Measured .435.
     
    Last edited: Jul 9, 2017
  6. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
  7. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    did you test it ?
     
  8. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    I did. I pulled it from the circuit and used the diode test on my DMM. It measured .435V. From researching I believe 1N60 Germanium Diodes should have a forward bias of .32V. It would seem the existing diode is failing. If Im wrong please educate me.
     
  9. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    the vf will very likely change with temperature . i looked up the data sheet and it only states max vf which is 1v .
    germanium diodes have a lower vf than silicon ones . as for a replacement i would try and source an original or find a close match in germanium ..it could be a 4148 silicon would suffice .
     
  10. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Thanks. I think I will get the originals to see how it works.
     
  11. pete_mac

    pete_mac Super Member

    Messages:
    2,723
    Location:
    Sydney, Australia
    I have had excellent success with increasing the size of a particular capacitor on an AU-7500 (I think?). It doubled the delay time (from about 2 seconds to 4 seconds) and provided sufficient time for DC to settle, eliminating any popping.

    I'll see if I can dig up details of exactly what I did.
     
  12. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Thanks for any info you can provide. I plan on upping the timing cap but also want to make sure I'm not masking other issues that might come back to bite me later.
     
  13. pete_mac

    pete_mac Super Member

    Messages:
    2,723
    Location:
    Sydney, Australia
    Just checked... on the AU-7500 I doubled the capacitance of C902 from 220uf 6.3v to 440uf and it worked an absolute treat!

    This cap is the equivalent cap to C23 on the AU-7700 (which is 470uf 6.3v). I'd suggest increasing the capacitance by at least 220uf-470uf to see how you go. As there was sufficient room on the rear of the AU-7500 PCB, I tacked the additional cap onto the solder trace side of the PCB to begin with. The 7700 is more cramped though!
     
  14. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    I pulled the 470uf and put in a 1000uf 6.3V to see how it would do. It double the relay time. About 4sec. I am still going to go back thru and replace the d23 diode to see if it is causing issues.
     
  15. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    does it still pop ?
     
  16. pete_mac

    pete_mac Super Member

    Messages:
    2,723
    Location:
    Sydney, Australia
    No worries!

    To be honest, it's a very common issue - the DC often fluctuates immediately after amplifier turn-on, and settles within a few seconds. Allowing more time before the relay engages should generally alleviate the pop.
     
  17. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Yes, but not as bad. So I still want to track down the issue. Diodes are arriving today. I will replace d23 to see if that helps.
     
  18. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Installed d23 last night. No change. Still speaker pop. Rechecked DC offset, good. Am thinking I will recheck D.C. Bias but that requires some desoldering, will do later today.

    Any other suggestions?
     
  19. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,808
    Location:
    uk.. the middle bit
    i would up the value of the timing cap to get more like 4 seconds . then see what happens .
     
  20. micaiahm

    micaiahm AK Subscriber Subscriber

    Messages:
    69
    Location:
    New York
    Already done. 1000uf 6.3V. Improved the delay. Speaker pop not as intense, but still there. It occurs as the relay engages.
     

Share This Page