Tweakers' Asylum

sansui hot to the touch

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walkstoslow

A

I recently found my volume control maxed out on my Sansui integrated amp (au 317).
The heat sinks felt like they were very warm, after many years of no noticeable heat.
I took a look at the DC offset, and the bias, things looked ok (Dc<1.5MV AND THE bias,11.0MV) not perfect, I adjusted both numbers closer to nominal.
I then hooked up my signal generator to the aux inputs, my oscilloscope to the L^R speaker outputs, and checked the wave form from 400hz to 20khz the form and p-p voltages stayed consistent.
I am thinking things are ok..Thoughts on any thing else I should check?
What a great hobby this is...

Follow Ups:

It was probably oscillating at a very high frequency - Chip647 08:31:29 01/14/25 (7)
which would drive the amp hard but be silent.
- RE: It was probably oscillating at a very high frequency - walkstoslow 11:08:10 01/14/25 (6)
  How should I check for the high oscillation damage?
  My signal generator only goes to 20khz.
  Also what components could oscillation affect?
  Passive, active or both?
  I am concerned about pre-amp drivers, and how to go about checking them.
  When I tried to check pre-amp output, I discovered my 0'scope is not sensitve enough to see the pre-amp signal.
  That is why I checked the amp output waveform.
  Can I assume that by the amp waveform looking good, the pre-amp must be good also?
  I have been studying electronics for years, not professionally.
  I know just enough to be dangerous.
  I appreciate your time and knowledge.
  Any thoughts are appreciated.
  This is a great hobby....
  .
  
  Edits: 01/14/25 01/14/25
  - RE: It was probably oscillating at a very high frequency - Chip647 09:01:08 01/16/25 (5)
    The oscillation would be 50Khz to 300khz. You would need an oscilloscope to see it. If your amp has been stable outside of that one event with the wide open volume control, I would not worry about chasing it down.
    - thanks for your expertise...one more question..... - walkstoslow 11:50:37 01/16/25 (4)
      I have been checking my dc offset the last three days,
      i have noticed that the offsets are within .5 mv of each other, though they are opposite polarities.
      I was thinking that since my amp is right side pos. 41v and left is neg 41v
      that this makes sense.
      But it seems loke when I set dc offset a couple of weeks ago they were both pos 41v, i might be wrong.
      What regulates the power supply besides the transformer output, diodes (bridge & zener) and transistors in the power supply?
      Thank you for your time, I am trying to understand...
      
      Edits: 01/16/25
      - RE: thanks for your expertise...one more question..... - Tre' 19:12:41 01/16/25 (3)
        
        In Reply to: RE: thanks for your expertise...one more question..... posted by walkstoslow on January 16, 2025 at 11:50:37
        
        41 volts DC at the speaker connections? That would be very very bad.
        
        Tre'
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        duh...4.1mv...nt - walkstoslow 20:01:31 01/16/25 (2)
        
        In Reply to: RE: thanks for your expertise...one more question..... posted by Tre' on January 16, 2025 at 19:12:41
        
        ,t
        
        4.1mv, + or - is just fine. nt - Tre' 14:48:42 01/18/25 (0)
        
        In Reply to: RE: duh...4.1mv...nt posted by walkstoslow on January 16, 2025 at 20:01:31
        
        .
        Have Fun and Enjoy the Music
        "Still Working the Problem"
        
        They can float around a little around the null - Chip647 12:21:06 01/17/25 (0)
        
        In Reply to: RE: duh...4.1mv...nt posted by walkstoslow on January 16, 2025 at 20:01:31
        
        Cant really draw any conclusions about being a few mV positive or negative. You likely have a servo that is trying to zero out the offset.

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