Sansui AU-X11 Restoration

Discussion in 'Exclusively Sansui' started by SanthoshA, Sep 21, 2017.

  1. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    If thermal protection is being activated, assuming you don't notice any excessive heating, then the fault is in the protection circuitry not the bias setting point or procedure.

    From 'stone cold' my AU-X1 bias starts at around 40mV, and slowly (~10 minutes) tracks down to the bias set point the last time I checked this behaviour. I can't remember whether I used 20mV or 25mV as the set point. (I am rechecking this now).
     
    Last edited: Nov 9, 2017
  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    It looks like I used 20mV as the set point, I will try it set to 25mV.
     
  3. SanthoshA

    SanthoshA New Member

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    strange though, for me though the bias starts gradually increasing from 4.5mv to set bias voltage in around 10 to 15 minutes.

    It will be easier if i can make a plot or graph , so we know how it works, but i am pretty sure it starts low and reaches the DC bias set, not the other way round wherein it starts high and drops to set voltage. can also check if the cut off from 40mv(at cold start), to set bias voltage at 20mv. Does it happen gradually or is it is a sudden drop, say it reaches from 40mv to 35mv and then suddenly drops to set bias voltage which is 20mv.

    Should it not be the other way around ?
     
  4. Ronito6

    Ronito6 Super Member

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    For the crowd sourced X11 thread I am doing, are you measuring your bias voltage at the top side header or through the bottom at the output transistor emitters?
     
  5. SanthoshA

    SanthoshA New Member

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    The test points at the header to be precise, i am afraid to even open it up and do the test say at the output transistor emitters. Is it the voltage across the collector and emitter.?
    Where exactly do you measure it at the emitter , if you can tell me, i will do a test and post back the results.
     
  6. Ronito6

    Ronito6 Super Member

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    On the X1 its easy. The SM tell you where to measure, and what to adjust to.

    Also...very commonly on the X1, the top side test point is deactivated.

    So looking at the X11 driver in my hand, and knowing how Sansui deactivated the top side test point on the X1 (thank you Willy6), direct access to the output transistor emitters to be measured should be the emitters of the inner-most pair of output transistors.
    [​IMG]

    So if you connect your multi-meter to the receptacles that accept those emitter prongs, (before the emitter resistors on the emitter resistor side of the driver heat sinks) you should get the same readings you get from the topside test point.

    (Measuring directly from the bottom is not really necessary if your topside test point is OK. But I think its good to know where it is getting its voltage from.)
     
    Last edited: Nov 10, 2017
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  7. SanthoshA

    SanthoshA New Member

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    Sorry to be frank, i believe i am asking too many questions, i am quite a learner, but not an expert.
    Say when we measure it at the emitter's directly, this should be between a NPN transistor's emitter and a PNP transistor's emitter right.
    Going by the below pic wherein i marked the test points in red square , can you confirm if they are the right ones.
    Just to re-confirm my understanding, thanks for the information.
    By the any differences in the pre-amp board of the X11 compared to the X1.?

    Credits, to fellow member @Harolda, for the picture below.
    emitter voltage measurements.jpg X1 Schema.jpg
     
    Last edited: Nov 10, 2017
  8. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    When I power the amplifier on i.e. from 'cold' the bias is at ~40mV - gradually this reduces to wherever I have set the bias - currently I have it set at 25mV as a set point. In my experience you always set bias in SS amplifiers after a warm up - around 20-30 minutes is normal, the variation is also normal - but if it happens suddenly then something is wrong. It is this way with the AU-X1 but with other amplifiers it could be round the other way, depending on their topology and design, I don't see any reason for the AU-X11 to be different to the AU-X1 in this regard.

    NB: I found the TP socket wiring error and corrected it on my AU-X1 - I find it very useful to have them operational.
     
    Last edited: Nov 10, 2017
  9. Ronito6

    Ronito6 Super Member

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    Yes. You got it. Just follow THOSE black and white wires to their respective sources.

    Where did you source that photo BTW? (Adding provenance is best practice.)
     
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  10. SanthoshA

    SanthoshA New Member

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    Found it and have added credits to the picture.
    Thanks for letting me know .

    By the way the bias in your X11, does it increase in a cold start say from 40mv and then decrease to set value say 11mv. Just curious to know how it is in yours.
    Else i am going to check the driver boards for faults in mine.
     
  11. Ronito6

    Ronito6 Super Member

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    I didn't take note of it, but it sounds very similar to what I remember. I was more concerned with how and if it maintained voltage once dialed in. (It did.:D)
     
  12. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    A clean and re-application of heatsink compound seems to have a beneficial effect on bias drift, especially if this includes the bias tracking transistor and its method of being thermally connected to the main heasink assembly.

    I would be interested in the 'stone cold start' bias mV - and 'fully warmed-up' mV figures on your AU-X11 amplifiers, if you happen to measure this. ;)
     
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  13. Ronito6

    Ronito6 Super Member

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    Fresh thermal grease...I’ll second that.
     
  14. SanthoshA

    SanthoshA New Member

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    Now, we know where the test points , are actually wired to, i feel unsafe to use alligator clips to take measurements, just worried of a short.
    And i have people moving in and around my place, when i start to work on it, just in case they move the wires around or it shakes a bit, the results are going to be drastic.

    Have ordered these from ebay.in, and am waiting for them to reach my place.
    Probably this is the only amp which i am going to take 30 minutes for biasing.

    Test Point Connectors.jpg
    Once they reach my place, i will take the bias measurements and post them here, hopefully it is a fits into the male test point pins.

    Meanwhile there are couple of other points which i wanted to post , regarding the preamp section.
    1. The outputs from tape 1 & tape 2 recording terminals, are at a fixed voltage, meaning the variance in big preamp knob has no impact on the pre outs for tape 1 and tape 2 rec.
    2. The more interesting part is that when you have source connected to AUX, and then check the pre amp outputs jacks in the back of the amplifier, there is no voltage produced, rather say the signal is absent.
    The only way to enable the signal at the pre amp outputs 1 & 2 is to change the amplifier mode from (Integrated to 1 or 2), this disables speaker outputs from the X11.

    So if you need the amplified speaker outputs from the X11, and also the preamp outputs from the X11, the only way to do this will be to loop the connections from preamp outputs 1 to external power amp inputs 1. ( i haven't tried this yet, but this is just my understanding )
    Or in case you have an external analog eq, the preamp outs from the X11 to analog eq, outputs from analog eq to external power amp input 1.

    Many of you might already know this , but i have just added this to my thread to keep track on some basic tests, please ignore if not relevant.
     
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  15. slimecity

    slimecity Super Member

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    That solution looks awesome SanthoshA. I noted the middle pin in my bias testing block wasn't connected to anything. Presumably its there for stability, so it doesn't move around. I pulled it anyway and I use alligator clips on mine to measure my wildly swinging bias. Doing that made things easier.
     
  16. SanthoshA

    SanthoshA New Member

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    Nice, mod, this inturn avoids short with the middle terminal, i went through Mr.AMP8 posts, the onces where you can see PCB traces in the rear. Ideally the middle pin is not connected to anything.
    Wondering if it has a mod potential, you could use a connection to other test points in the PCB wired to middle pin as it is a dummy, but ain't worth the risk through, better safe to remove the middle pin when using alligator clips. Apart from the middle, another key point is the pin beside the heat sinks, its even more riskier to have a short there too. I would even recommend to get these connectors, these are cheap stuff, but will come in handy for these measurements.
    And for an amp like the X11 with no service manual floating around, better to be safe.

    I have had good results with the alligator clips, but the problem, is i need to keep verifying the connection atleast 5 times per side, to ensure there is no short(with the middle pins and also the heat sink), these clips provide us an easy connection and we can negate effort put into checking the alligator clips for short.

    Probably i am just too afraid for it, and the measurements can be taken easily with the alligator clips too.
     
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  17. SanthoshA

    SanthoshA New Member

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    Here we go again, trying to source the 2ST5949, from littlediode, i had trust in them , and was hoping i will get the real transistors.
    They inturn have shipped me fakes for an insane price.

    littlediode.jpg Fake 2ST5949.jpeg

    I have little hope with the online sellers and the ebay sellers.

    Those who rely on littlediode for spares please refrain from them.
    Mouser and Digikey are very reliable though.
    The price in above snapshot if for 4 transistors.

    I have created a pay pal case for the same, hopefully i get the refund.
     
  18. slimecity

    slimecity Super Member

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    Sorry to hear that. I have been coincidentally reading a few posts today about avoiding Littlediode, for this exact reason.
     
  19. Ronito6

    Ronito6 Super Member

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    There is a Yahoo Auctions Japan transistor seller who goes by the handle of laserdiode.

    He is good source. (1808 positives and 0 negatives

    A shame he chose a name so close to that dubious one.
     
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  20. SanthoshA

    SanthoshA New Member

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    Guys any idea which trimmer pot , amp8 uses for his builds.?
    upload_2017-11-15_18-40-43.png
    Credits: Mr.Amp8
    I am working on a list to re-build the boards of the X11, and will share the file once finalized, if some can help with the model numbers for the above potentiometer i will be extremely grateful.

    Meanwhile are the below capacitors suitable to replace the black flag's?
    There are from Cornell Dubilier - CDE


    10pf 2 CD15CD100DO3 - Mouser Part No
    47pf 2 CD15ED470GO3 - Mouser Part No
    33pf 1 CD15ED330JO3F - Mouser Part No

    If there are other alternatives to consider please let me know.

    Thank you!.
     

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