AU-317 - recap/upgrade of F-2754 and F-2752 boards

Discussion in 'Exclusively Sansui' started by Karl vd Berg, May 17, 2017.

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  1. Karl vd Berg

    Karl vd Berg Super Member

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    Hello to all Sansui fans,

    A quick thread with some pictures of a classic "little" integrated, one my favorites... I want to thank to all those who shared previously info on various threads... :)

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    ... and I have had another (3rd unit, so far) AU-317, first version, on bench and this one is in quite good cosmetic condition. However, the sound was "cutting off", sometimes on left channel, sometimes on the right. Chances to be only the relay is remote, in all the other units I had the relay worked pretty good.
    So I decide to work on it, inspect where the problem was and rebuild the PSU, plus the regulator to the preamp part and the protection circuit by replacing and upgrade all the electrolytic caps, some ceramic ones, the Zeners and small signal diodes, the trimpots, some resistors and other components we'll see along the posts...

    I'm working on F-2754 and F-2752 boards here, since most of the time I use "Line In" stuff (tuners, CD players, DACs, other preamps, etc).

    So, this is the unit under the cover...

    [​IMG]

    Voltage masurements on TM22, TM23 and TM24 cable connectors showed different DC voltage to the preamp boards, something like 27Vdc in one channel to ~31Vdc in the other, so I decided to start around the regulator.
    [​IMG]

    Disconected and cleaned the main F-2754 board and there were cold and broken solder joints everywhere...
    [​IMG]

    On the left, TR601 (2SD356), at regulator circuit...
    [​IMG]

    Cold/broken solder joints in other locations...
    [​IMG]
    [​IMG]
    [​IMG]

    Before reflow the cold/broken solder joints, I started checking the electrolytic caps and their values to see how they drifted over the last 4 decades.
    Below, C608 (220uF/35V):
    [​IMG]

    The cap was replaced to 270uF/63V that fits in size... (thanks to Leestereo for the suggestion here)
    [​IMG]

    Then, ZD601 and ZD602 - 30V Zeners - had to be replaced to BZX55C30 ones (thanks to AUD101 for the suggestion in previous threads).
    [​IMG]

    Next, the four capacitors (C609~C612) that feed the preamp board are essentially a couple of 147uF caps arranged in parallel (100uF + 47uF / 35V). I upgraded these with two of 150uF/ 63V, low ESR.. (thanks to Leestereo for the suggestion here)
    [​IMG]

    And here we have the regulator rebuilt, fresh solder joints (the new Zeners are in a next picture)...
    DC voltages are +/- 30V! :)
    [​IMG]

    Now, C605 and C606 (470uF/50V) with the dreadful glue, that "contaminates" the the surrounding components, were also below capacitance value...
    [​IMG]

    These - dated 1975 - were replaced and upgraded to a higher value, 820uF/50V. (Thanks, Leestereo).
    I wanted to use this "new product" (dated 2016) from Nichicon, UHW series, low ESR.
    [​IMG]

    Their rectifiers (D606~D609) were the 10D1 types and were replaced and upgrade to STTH208 types (thanks to Hyperon and Avionic for suggestion in previous threads)
    [​IMG]

    The same STTH208 replaced also D601 (rectifier for the protection relay circuit), and D610 as the original was also 10D1 types...
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]

    And here we have the power supply section rebuilt, plus the relay and protection circuit and regulator for the preamp... My only doubt here is that the bypass caps 1uF/100V (C901, C902) should remain in parallel with the big ones, or they are not necessary with modern 12,000uF/63V capacitors...
    [​IMG]
     
  2. Karl vd Berg

    Karl vd Berg Super Member

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    Moving to the power amp section, here a partial shot of it.
    [​IMG]

    The 150 ohm fusistors (R35, R36, R45, R46) were above their stock value and will be replaced with new ones, rated 1/3W (Thanks to Skippy124 here).
    [​IMG]

    The "fine-tuning" trimmer (VR03) showed max resistance value under its stock value..
    [​IMG]

    VR01, instead, showed max value above its stock value...
    [​IMG]

    For C25 and C26 (1uF/50V) this time I wanted to try Nichicon MUSE.
    And for the Mylar caps C27 and C28 (0,047) I used some PP caps from Wima...
    [​IMG]
    [​IMG]

    Here, a partial shot showing some components soldered, includind the 22K negative feedback resistor (R31 and R32) that was posted a while ago here.
    Capacitors C15 and C37 (3pF) were "upgraded" with C0G ones. DC offset is pretty stable. :)
    [​IMG]

    Below, part of the power amp section rebuilt, showing the 18V Zeners (ZD603~ZD606) that were replaced with TZX18B-TR types.
    [​IMG]

    Before I replace any transistor, I want to be sure if it is really needed when all the electrolytics were replaced in this board and the solder joints are now fresh. I have, however, ordered some parts which could replace some of them in case of failing... I can change yet some parts in the F-2754 after fire it up for tests...
    KSC2690AYS, KSA1220AYS, KSC2316YTA, KSA916YTA, 2SC945, 2SC2240, etc...
    [​IMG]
    [​IMG]
    [​IMG]

    Coming next, the F-2752 board... :)
     
  3. vsat88

    vsat88 Like my Bluetooth ?

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    Your documentation is beyond belief. I mages are clear as a bell. It takes time to do such good work. I am amazed at you guys who can do such as this. Just you being able to remember who recommended the parts installed and giving credit to them blows my mind. I now bow to the Stereo Gods !
     
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  4. Karl vd Berg

    Karl vd Berg Super Member

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    After a while, here's a quick update on the F-2752 board with images...

    In the end I used two Silmic II for C9 and C10 (4th. pic), instead of the Wimas in that positions... Other works done were shortening those messy black wires (2nd. pic), cleaning pots and switches and full solder reflow. The amp is playing now, I'm really happy with the results... and I'll keep this unit.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

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    [​IMG]
     
  5. roger2

    roger2 . Subscriber

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    Beautiful pics! Is tinypic a free image hosting site?

    I also like how you color coded info on the schematics snippets and overlaid info in some of your images.
     
  6. Karl vd Berg

    Karl vd Berg Super Member

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    Yes, Tinypic does it for free. :)
     
  7. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    super cool!
     
  8. Karl vd Berg

    Karl vd Berg Super Member

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    Forgot to mention, R29 (2.2k) was measured 2.1k and R30 (right channel) was on specs. May not be that relevant, but a few other resistors have some values different from their stock values. Not sure if this happened in other amps from the AU-x17 series.
     
  9. Overundr1

    Overundr1 AK Subscriber Subscriber

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    Nice detailed rebuild sir, well done.
    -Lee
     
  10. RobertDL

    RobertDL New Member

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    Info is detailed, but the pictures can't be seen. Please if something can be done.
    Thx

    P.S. It seems that everybody can see the pictures and I can't. Strange.
    The firewall blocks the pictures.
     
    Last edited: Oct 4, 2017
  11. The Fuxtor

    The Fuxtor AK Subscriber Subscriber

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    C9 and C10 ended up with electrolytic caps? Was there a reason not to use Wimas in that position ? No room perhaps?
     
  12. LBPete

    LBPete Rolling Along Subscriber

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    A beautiful write up and great pics! Well done.

    - Pete
     
  13. Karl vd Berg

    Karl vd Berg Super Member

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    Yes, later I changed them to some Wimas indeed. :)

    C605 and C606, I changed to Panasonic FM 560uF/63V; (not totally convinced with the 820uF in that position)
    C11, C12, C23 and C24, changed to Panasonic FM 680uF/63V; (same reason as above)

    And the main rectifiers D602~D605 were changed to STTH4L06 - 600V/4A - types (because I had few of them)

    Thank you all
     
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  14. LBPete

    LBPete Rolling Along Subscriber

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    Photobucket did it for free to until they decided otherwise. This is a great write up, it would be a shame to loose the images if Tinypic changes their "free" policy like Photobucket.

    - Pete
     
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  15. Karl vd Berg

    Karl vd Berg Super Member

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    Yes, that's true. In the past I used another image hosting site (Imageshack) for a 100+ images' recap an Yamaha CA-810, here. Nearly all gone unfortunately. Some can be seen in the last page. That was a slow process (for every step, a picture with camera on mini tripod, flash plus available light, etc), a massive effort that took me few weeks and loads of good info. All gone and I relied on the hosting site... Quite a few people emailed me later asking for the pics.

    Since then, I'm using Tinypic (so far, so good), but keeping all the images. :)
     
  16. LBPete

    LBPete Rolling Along Subscriber

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    It has happened a number of times with images hosted on AutoKarma too. The images in a number of my older threads were lost in server crashes. Be sure to save the originals especially after all that effort.

    - Pete
     

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