Sansui AU-X11 repair and restoration

Discussion in 'Exclusively Sansui' started by smurfer77, Sep 23, 2016.

  1. smurfer77

    smurfer77 AK Subscriber Subscriber

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    I picked my wife up from the train station today and had to warn her... there is a monster at home. The box is marked "heavy 69lbs". I've had a 110lb amp before, but this will be the heaviest amp I've worked on myself so far. What is the monster? Well from the title you already know it is a Sansui AU-X11. And, although I have several other projects unfinished, I've never worked on any of the 'newer' sansui and can't wait to get stuck in. The amp is meant to be stuck in protection mode. So here we go on another adventure. Am very excited to be working on something completely new to me. (In fact, I've never worked on a Sanui modern enough to have a relay!)

    The unit took a hit in shipping, but nothing too bad... the usual minor damage to wood side panel corners. After taking over several panels and covers I get to see the beasts guts. Very impressive inside. 80,000 uF of caps sitting right in the middle. Very beefy looking overall. What is immediately obvious is that the chassis ins't that beefy. It's actually pretty flimsy compared to what I'm used seeing inside of the older amps. Surprising for a unit carrying such heavy iron etc. You can flex the chassis with one finger! Additionally, the material rusts easily. My unit has the typical surface rust you see on almost all images of AU-X11. There is even some rust on the main transformer. Anyway, I will get to all of that later. I also see a fair amount of flimsy cabling and poor design in terms of mechanical and electrical reliability. I will do some rewiring and get rid of some of the crappy ribbon cables used (you know the type that you touch and it breaks the wire at PCB end because the cable housing is slightly inflexible and it stresses at the point where the exposed wire meets the housing). Oh, and I see some of the nasty glue used on caps eating away at resistor legs, especially on the board (presumably tone/preamp) behind the front panel - some of those resistor legs have turned into a frothing green mess. So after repair of the main issues and getting sound going nicely, I think a restoration of all boards is probably in order.

    The machine was meant to be in protection mode. But I look around a bit before trying to bring it up... and I can't find anything nasty looking. So I fire it up, wearing safety googles, half expecting something to explode in my face as I'm leaning over to keep an eye on things, going between checking meters and watching for magic smoke related issues. As I turn up to about 40 V, CLICK, a relay triggers and I'm out of protection mode (NICE!), then at 70-80V a few more clicks as the other relays tick over. So far, so good.

    I turn on a source and use my workshop speakers (a couple of woofers from some parted KLH 17 speakers sit permanently on my workbench... no need to risk any speakers I care about). Right channel is weak but has sound, left channel has nothing. I twiddle the volume knob a bit and the right channel come on strong, and I start to think about what output relays the machine has that might need cleaning. However, I attempt to bias up and right channel is fine, and left channel is stone cold. Nothing. So the intermittent right channel is something to do with the volume pot. Confirmed by further fiddling (I can make the channel weak/strong by pushing the volume knob without changing the volume setting... so I can forget about the output relays for now).

    I know nothing about the AU-X11 until today. So let's see what happens. If anyone has schematic or manual, let me know. I assume the manual would be in Japanese... I may be able to translate it if someone gets hold of it.

    Okay, so summary is: (1) fix volume pot intermittent right channel issue. (2) Left channel dead: check power supply to left driver/outputs, and if that's good pull the board and see what's what. On that note, Stereofun (and others) did you end up finding a supply for the high speed outputs (I remember you had a thread on something about that a while back)???

    And, those of you who know me will not be surprised..... many pics to come.
     
    Last edited: Sep 23, 2016

     

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  2. Ronito6

    Ronito6 Super Member

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  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Oh yes :lurk:

    I think it will benefit you to read the three (yes 3) fairly recent AU-X1 restoration threads and also the one AU-X11 restoration thread, there is some priceless information illustrated in those threads.

    Good luck.
     
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  4. mjs1

    mjs1 AK Subscriber Subscriber

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    Search and you will find. OP transistors are currently available from a reliable source if you act quickly enough.

    Marc
     
  5. stereofun

    stereofun Super Member

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    Well I found them alright....... 2st5949, 25mhz npn TO-3 - but they were fake.
    I bought them through UTsource, which I initially thought was a vendor, rather they are just a middleman, so my transistors ended up coming from a Chinese outlet with bad English, located in the Sichuan Province :dunno:

    Good news is that we can plenty fast transistors, - just not in the TO-3 format.

    Check out this thread from DIY Audio - The thread is really interesting as it links to some examples of how TO-220 styles are adapted to be mounted on a TO-3 heat sink. (post 6,7)
     
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  6. Ronito6

    Ronito6 Super Member

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  7. Kale

    Kale AK Subscriber Subscriber

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    Just one small correction... those last two pictures was made by me. I made that adaptation from TO3 to TO3P, I thinking that somewhere I still have some numbers of those transistors. I glued together that aluminum piece to the body of transistor to get better passive cooling and to get better distribution of fixing force (not to only one point, where is screw). The glue was heat transfer glue. Those two isolation pieces on base and emitter legs are made of teflon.
     
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  8. Ronito6

    Ronito6 Super Member

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    Thanks for the correction.

    I missed the Kale021 in the credit line.

    So [​IMG][​IMG][​IMG]to you!
     
  9. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Thanks for all the info. It's really appreciated since this era of Sansui is new to me. I've started study by devouring Kale's thread on the AU-X1 and boy, what a thread! I have a lot more tabs open in the browser to study tomorrow.

    I did quick check the left outputs and driver board have power supply ok and all looks good. I did then pull the output transistors on the dead left channel today. Short circuit between base-collector on all four outputs. Will inspect driver board next and see if anything is amiss there.
     
    Last edited: Sep 24, 2016
  10. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Note the sticker on the side of the packing box:
    [​IMG]

    Sadly it has taken a hit on both the rear top corners during shipping:
    [​IMG]
    [​IMG]

    I do plan to deal with the cosmetic issues, but that is extremely low on the totem pole right now. I've spent most of today reading all of the various recent AU-X1 threads and learning as much as I can from that. One this is clear, I need to have some serious respect for this project and do things properly. Oh here is the pic of the unit from the front. Despite the wood panel damange, she is a looker:
    [​IMG]

    One thing I noticed when I took the cover panels off is one missing screw from the outside. Well I think I found the screw. Can you see it? Now maybe it's clearer why they put those grills on top of the driver boards (above and below the 8 big caps in middle), not only for human safety perhaps. Note the surface rust. It's really typical of these units. Every single unit I have seen online has this. The AU-X1 has a painted chassis instead right? Does the AU_X1 also use such thin flimsy (relative to the weight of components) material?
    [​IMG]

    Here is a closer pic in case you missed the screw:
    [​IMG]

    Closer view of chassis surface condition. The oxidation is really not as bad as it looks... not deep at all. I love the SANSUI ELNA on top of the main supply caps. Might have to scan/replicate if i replace those caps.
    [​IMG]

    Here is a sneak peak of the death glue on the preamp board. You can see some resistor legs affected.
    [​IMG]

    Here are the shorted output devices NMA1717 and NMC1718 (2 of each per channel, I.e. four transistors per channel, compared to 6 on the AU-X1).
    [​IMG]
    [​IMG]

    To get the output transistors out you can remove just 3-4 wires, and slide the output section out enough to unscrew the output transistors on the rear of the big heatsinks. However, the minimum to get the output section fully out is 8 wires or so. In fact, the 3-4 wires option to get the output transistors only works for the output section closest to the rear of the unit (left channel); on the right channel (output section located nearest front of amp) the driver board is spun around 180deg in orientation and the cabling is such that you really need to remove all wires and take the entire lot out to get at the output transistors. Taking lots of pics, so let me know if anyone needs more details at some point. Anyway, I took the left output section all the way out, since the outputs are shorted and I know I need to inspect the driver board.
    [​IMG]

    Have started to peek around the driver board a bit today, but got distracted reading all of the AU-X1 theads and learning what I can there. Will post what I find on the driver board soon, but one thing I can tell you is the driver board varies more from the AU-X1 board (and has a many more components) than I expected. But maybe that's a good thing if the some of the reported issueds where addressed in updates here (although I know others report the oscillation issue is related to grounding on the preamp). Will do my best to highlight differences between AU-X1 and AU-XII, and provide as many details as possible since there isn't a schematic out there (and very little other information in general) for the AU-XII that I'm aware of.
     
    Last edited: Sep 25, 2016
  11. Ronito6

    Ronito6 Super Member

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    Kewl!

    • Fun fact: The phono section cards in the X1 and the X11 are swap-able. So an X11 cards can live happily in an X1, and vice-versa.

    • Much (MUCH) less fun fact: The phono cards in the X11 have a coating of thermal paste on top of the heat sinks to improve heat dissipation from the cards through the metal hood that covers them.

    I added thermal paste to the tops of the phono cards of my X1 and the heat transfer improved quite a bit.

    BTW: Great pics [​IMG] and looking forward to more!
     
    Last edited: Sep 26, 2016
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  12. smurfer77

    smurfer77 AK Subscriber Subscriber

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    Thanks Ronito. I usually use a fancy camera for taking my pics, but for this thread I'm playing with an old Olympus XZ-1 point and shoot. It's pretty good at macro!

    Good to know some the phono board is interchangeable.

    BTW the AU-X11 seems to way a few pounds more than the AU-X1. I clocked it in at 63lbs. Don't trust that too much since the bathroom scales are not very trustworthy, but I believe it's a couple of lbs more than the AU-X1. And the driver board is really quite different, at least to look at.... so many more components. Will post that shortly, but boy... some damage was done on that board! Just trying to find the origin of the issue, before getting together the parts list for a rebuild.

    But before moving onto the driver board damage, I just wanted to post a few more pics of the layout. Might be of interest for those with AU-X1 to see some little difference, and good for future reference should one of us with an AU-X11 need some reference pics for putting wires back in the right place.

    Here is the driver board from the top. I've already removed the ribbon cable, which you can see at the bottom. There are four wires you can see from the top that need to be removed to truly remove the output section.
    [​IMG]
    [​IMG]

    If you don't unsolder those 4 wires it is possible to rearrange the cable routing around those big caps, such that you can remove the output section into the following position (pictured below), from which you can remove output transistors. However, as I mentioned, I found this possible only with the Left channel. For the Right channel it wasn't possible to quite reach the output transistor screws because the cable routing is different due to the driver board being flipped around.
    [​IMG]

    And for either channel, you can't get the driver board PCB unscrewed and out unless you remove 5 wires attached at the bottom. And two 3pin connectors, already removed from Left (right side of pic) channel.
    [​IMG]

    A close view of the cables to the driver board and outputs. The twisted red/blue wires are from the four 10,000uF caps (4x for each independent channel) providing the +/- 69 V DC output supply. These caps are setup the same way as in the AU-X1, with 2 big caps on negative side, and two big caps on positive side, and a little 1uF over each pair of big caps.
    [​IMG]

    Notice anything funny with the mounting of the output heat sinks?
    [​IMG]
     
    Last edited: Sep 26, 2016
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  13. Ronito6

    Ronito6 Super Member

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    "...notice anything funny with the mounting of the output heat sinks?"
    The big heat sink seems anchored to the chassis at only one point on that side. WTF?

    I'm also wondering about the bridge of film caps across the output transistor rails where the red and blue wires are soldered onto the rails.

    [​IMG]

    I shall take a peak in my X11 to see if its the same. I'll post pics of what I find.

    I'll be home in two hours and then we shall see if any of this is or isn't amiss in your machine.
     
    Last edited: Sep 26, 2016
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  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I found a couple of polystyrene capacitors in amongst the emitter resistors of each channel of my X1, across the supply lines, I left them in place with a mental note to 'improve' them at a later date. ;)
     
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  15. Ronito6

    Ronito6 Super Member

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    Yes. You are correct. The X11 apparently employs capacitors in the near the same spot as the ones in the X1.

    Here are the pics from mine, and they confirm that Smurffer's X11 is factory correct so far.

    The underside as a whole.
    [​IMG]

    Both driver heat sinks from below.
    [​IMG]

    The the missing bolt point for that one heat sink.
    [​IMG]

    Finally the caps on those rails.
    [​IMG]
     
    Last edited: Sep 26, 2016
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  16. ghamilton

    ghamilton Super Member

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    Images missing on last post. Thought you'd want to know.:)
     
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  17. smurfer77

    smurfer77 AK Subscriber Subscriber

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    EDIT: note that output bias current I mention in this post is 2x too large, because I didn't realize at this time that the AU-X1/AU-XII bias test points are over two emitter resistors, instead of one. So what I said about taking care setting bias voltage according to AU-XI manual because of AU-XII emitter resistor values being different stands. The target voltage I mentioned stands. But the resultant current would be more like 25mA, or so instead of 50mA mentioned in post below.

    Ronito, I also don't see your pics.

    Yes, on corner of the Left channel output heat sink is not screwed to the chassis. As you say it looks to be like that from factory. I don't know it. I can push the heat sink and move it around a bit with one finger. Here is what Amp8 did and I may try something along those lines:
    [​IMG]

    I have a question for the AU-X1 owners. X1 manual says 25 mV across test points for setting bias, but manual shows 0.33 Ohm emitter resistors in schematic and part list, whereas I think most of you (judging by pics from various threads) have 0.47 Ohm emitter resistors installed. Are you assuming the 25 mV is correct for the 0.33 Ohm or 0.47 Ohm? I.e. Did you assume the goal is ~75 mA or ~50 mA? Sorry if I'm being pedantic and it doesn't make much difference, but I won't be happy until I get your thoughts :)

    This came up partly because I saw in another thread that some folk are using the 25 mV from the AU-X1 manual to set their bias in the AU-XII, but the AU-XII has 0.22 Ohm emitter resistors on the power transistors so one would more likely want to use ~11 mV (assuming ~50mA idle is the target, or maybe 16 mV or so if you shoot for 75 mA.). For what it is worth I can tell you is that on my good (Right) channel, the voltage was sitting on about 10 mV before I touched anything. Also, I confirmed on Mr Amp8's pics that he also has 0.22 Ohm emitters in his AU-XII units.)
    [​IMG]

    Regarding the little caps across the big supply caps, I can confirm they are 1 uF value across each 20,000uF pair, same as in the AU-X1. Here is a pic of the present/stock situation:
    [​IMG]

    Here is one more pic from Mr Amp8 below. Looks like he kept the 1 uF caps but added some film caps of ~10uF value, as well as some electrolytics of value in the range of a hundred or so uF. Overkill? I know the community is a bit divided on the bypass caps, but 1uF paralleling 20,000 uF... seems like it could use some help from something a tad bigger. Thoughts?
    [​IMG]
     
    Last edited: Sep 29, 2016
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  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    They seem to follow the decade rule 1-10-100 supposed to be most effective in improving the filtering performance, I used to think that a film cap across each main filter cap was a very good idea. Now after reading posts by ConradH, from whom I have learnt so much, I now think a single film capacitor across each of the main PSU capacitors may not necessarily do what is claimed. I think much depends on the PSU of the amp in question and how the driver circuits are powered, often not from the same supply as the outputs, these would definitely benefit from some extra filtering in the right place (of the kind shown above) in my opinion.
     
    Last edited: Sep 28, 2016
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  19. Ronito6

    Ronito6 Super Member

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    Changed permissions to viewable by members.

    I think my pics should be see -able now.
     
    Last edited: Sep 26, 2016
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  20. Ronito6

    Ronito6 Super Member

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    The X1 manual that is used by all is for the first version of the amp. Emitter resistors seems to have been quickly upped by Sansui from what is stated in the SM.

    When I have time I will check the operating voltages of the drivers on my X11. I would be very surprised if they were not very near 25mv. Answer by this weekend.
     

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