Sansui AU-X901 Protection Mode

Discussion in 'Exclusively Sansui' started by sajjad amer, May 18, 2018.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Aha ! - nice

    Please check kR60, kR62, kR76, kR78, and if not already checked kR64 & kR66 - lift one end of each to check.

    Report and/or replace any that are faulty.
     
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  2. sajjad amer

    sajjad amer Active Member

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    As always you are spot on sir, R62 was open, I have replaced it with 100 ohm resistor and now I can adjust the bias and it's set to 16mv across all 4 output resistors.
    DC off set is 00.23 R and 00.19 L
    I have not touched KVR 2 at all, what's it's function?
    What should I do next?
    Thank you
     
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  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Ok, that's good news!

    kVR2 in each channel is to set the 'Cold to Ground' DC offset - my experience is that it is almost impossible to achieve anything like the setting accuracy claimed or required by the SM procedure. So I just set it as accurately as possible and leave it at that, it wanders all over the place and could be 1 or 200mV as set. It has no effect on the ability of the amplifier to come out of protection mode and doesn't seem to affect anything else as far as my investigations have shown.

    So at the moment the bias has been set with the amplifier powered via DBT, if you were to connect it to full mains now you could cause some damage - because the bias will obviously be set for a lower supply voltage overall, thus making the full mains bias far too much.

    So, the next thing to do is to turn down the bias.

    What I do here is to turn the bias down so that 'just a sniff' is visible on the multimeter i.e. between 0 and 5mV. - note again - this is FOUR adjustments.

    Let me know when you have done that.
     
    Last edited: Jun 3, 2018
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  4. sajjad amer

    sajjad amer Active Member

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    Thank you, I have reduced bias to 5mv on all 4 output resistors
     
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  5. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    OK - well, I am going to take a guess that there is nothing wrong with the protection circuit, and that it will operate normally when connected to full mains.

    Please disconnect any speakers, volume to minimum, no inputs connected.

    So, please connect the amplifier to full mains - and we'll see what we get. ;)
     
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  6. sajjad amer

    sajjad amer Active Member

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    Done as suggested, Still the orange protection light is blinking I am afraid. DC offset is 00.19 L and 00.10 R
     

     

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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Is this 0.19V L (or 190mV) and 0.1V R (or 100mV) ? - and where are you measuring - from the centre point of one dual emitter resistor kR68 (red probe) to centre point of the other dual emitter resistor for that channel also called kR68 (black probe) ? anywhere else may be the wrong place - especially at the speaker terminals = wrong.

    Once again a warning about probes - be careful.
     
    Last edited: Jun 3, 2018
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  8. sajjad amer

    sajjad amer Active Member

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    I am measuring at TP1, Pin 1 and 4. It is mV.
    measuring between the centre point of dual emitter and ground on each side it is -1.7mV
     
  9. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Are you able to adjust that at all? - just so we can be sure you are in fact monitoring DC offset.
    These are very low readings - possible - but nevertheless outstandingly low - so I am suspicious.

    Also the instruction to do this was wrong. TP1 pins 1 & 4 are correct, or the centre of emitter resistors as described above. (not centre of emitter resistor to chassis)
     
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  10. sajjad amer

    sajjad amer Active Member

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    Yes, I can adjust the dc offset using KVR1 (hot-cold) on both Right and left side. I can take it right down to 00.00 mV but my hands are not that good, it just shifts to +/- 00.50mV.
     
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  11. sajjad amer

    sajjad amer Active Member

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    Just to double check that

    Volume is minimum
    tone controls, zero
    speaker A button "on"
    Power Amp Direct is set to "normal"
    Source Direct Button is set to "on"
    CD selected as source.

    I hope this is how I should be attempting settings.
    Thank you
     
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  12. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Ok - that's fine.
    Yes, important ones are now bolded
     
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  13. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Just to check a few things:-

    If you alter the speaker select switches - can you hear relays clicking at the rear of the unit?
    You still have the flashing protector light ?
    Do you have headphone output? - plug in headphones if you have any? - connect a cd player or something and see if you have output.

    It is possible you will have speaker output as well ! - but with a flashing protection light. :)
     
  14. sajjad amer

    sajjad amer Active Member

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    • changing speaker select switches I do not hear any relay click.
    • I still have flashing protector light
    • I have connected CD player, there is no out put at headphone jack.
    Thank you
     
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  15. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    What led you to change transistors on the small protection board located on the power amp board? - I believe you changed 4 on one of the boards.
     
  16. sajjad amer

    sajjad amer Active Member

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    Yes, I did change them as Q31 was physically broken and I could see the innards of transistor.Please see post no 9, it has a picture of broken transistor.
    Thank you
     
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  17. sajjad amer

    sajjad amer Active Member

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    The substitutes on the protection board are from Digikey , however I do have the "original" or "original looking" transistors from China as well, shall I replace them in protection board ? Their hFE matches the original ones.
    Just a thought
     
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  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Ah yes, I see. - wow.

    I assume you checked the pin-outs on the replacements - and took note of the fact that there are 2+1 x NPN and 2+1 x PNP and they have to go back in the right places? - just seen your post above - no, no need to put the originals in - as long as you are sure of the above.

    I think we will stop here if that is ok with you, the next bit will be even more difficult and you will have to remove the rear panel to get at the protection board.
     
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  19. sajjad amer

    sajjad amer Active Member

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    Yes I was careful with the replacements, just to check again pin out of originals and replacement transistors were same.
    Yes certainly we will stop and I will wait for your next instruction as and when you like.
    Once again I am grateful for your kindness.
    Regards
    Sajjad
     
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  20. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    We have made good progress today, but I am beginning to think it is possible that the protection circuit IC TA7317P might have got damaged. (just checked they are still available :) - on ebay :( )

    Anyway - we'll take another look later today or tomorrow. ;)
     
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