Recapped Sansui AU-719 Protection mode help!

Discussion in 'Exclusively Sansui' started by RR--, Mar 3, 2017.

  1. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    I would look for film PP or C0G cap, I bet 100v will do (watch the size)
    KSC1815 is a better option
    10D2 is a 1.5A rectifier, the MUR240G do better than 1N4003 or 1N5392 (direct replacement)
     
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  2. RR--

    RR-- Active Member

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    Thanks again Hipocrates if you weren't 15,000kms away I'd buy you a beer.

    Updated list:
    F-3101
    • D601 & D602 10D2 (1S2227) replace with MUR240G Rectifiers 400V 2A
    • D607 10D1 replace with MUR240G Rectifiers 400V 2A
    • ZD601 replace with 1N5232B Zener Diode 5.6V 0.5W
    • ZD602 replace with 1N5234C Zener Diode 6.2V 0.5W
    • SCR601 2SF656 replace with MCR100-6A1G SCRs Silicon Controlled Rectifier with reversed pin order
    • TR608, TR609 2SC1313, replace with KSC1815
    • TR607, TR610, TR611 replace 2SA726 with KSA992FBU

    F-2926 and F-2927
    • VR01 3386P-1-101LF Bourns Through Hole 3/8IN 100 OHMS 10% 0.5Watts Square Trimmer Resistor
    • VR02 3386P-1-471LF Bourns Through Hole 3/8IN 470 OHMS 10% 0.5Watts Square Trimmer Resistor
    • VD1212 already replaced with 1N4148
    • C19, C20, C22 I02J 50 B_(N), WIMA 0.22uf 100 VDC 10% Film Capacitor
    I found this Wima as a replacement for C22, I mistyped 22uf above instead of 0.22uf: https://au.mouser.com/ProductDetail/505-MKP2D032201K00KI
    There's also a TDK C0G available in 0.22uf but it's only available in 50V.
     
  3. Karl vd Berg

    Karl vd Berg Super Member

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    Safer to stay with the higher voltage one (Wima), to this point.
     
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  4. AUD101

    AUD101 Parsley The Lion!

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    A pin for pin replacement that I have used for the 2SF656 (although overkill) is the X0402MF - note it is a TO202-3 package which is a little bulky - but will fit A-OK on F-3101 once raised clear above the near by resistors

    See pic below - X0402MF on AU-519 - F-2915 PSU board
     

    Attached Files:

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  5. RR--

    RR-- Active Member

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    Great thanks for the tip, that'll make it neater and easier.
    Yeah I think that's the safest option too. Thanks
     
  6. RR--

    RR-- Active Member

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    Quick update, I've put in every new part that I ordered excluding the bias and DC Offset trimmers and the problem persists. I'm trying to figure out a way to add the new pots neatly as their adjustment dial sits on top rather than the side. Soldering longer legs has been pretty ugly so far.

    I got it working for a few hours and I swear it sounds even better, it also behaves a little differently, when powering off the amp it's now silent instead of making a small pop. Also after successfully powering on the amp the protection light will continue to blink a little for a second or so.
    Anyone have any more thoughts? I'm not sure what else I can do to fix this amp.
     

     

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  7. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    What are the readings of the adjustments (page 3 of the service manuals) after the replacements
     
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  8. RR--

    RR-- Active Member

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    I'm wondering if these pots are just due for a replacement as they've always drifted. I hadn't adjusted them in a while so their measurements were:

    DC Offset Left 7mv (Should be 0mv +/-5mv)
    DC Offset right 10mv (Should be 0mv +/-5mv)
    Bias Left 20.8mv (Should be 23mv +/-1mv)
    Bias Right -18mv (Should be 23mv +/-1mv, I assume the schematics for + and - are printed incorrectly as it's not possible to set it to positive numbers)

    I reset these to all within the tolerances, the amp seems to be more reliable now although it still regularly trips into protection mode.
    Readjusting the DC Offset is a nightmare, even a slight tap of my screwdriver will send the value 300mv in either direction.

    Also a strange thing, I noticed in this picture that a fuse had blown, I replaced the fuse but it seems to have made no impact on the protection circuit issue. I've been testing the amplifier all day and unfortunately it is still just as intermittently unreliable.

    Here's some before and after photos too.
    [​IMG]
    [​IMG]
    [​IMG]



    Also you were correct, there was one lifted solder joint, however I don't think it was causing any problems as it was still very strongly connected with the trace on the board, I glued it down with some electrically conductive glue and thickened the trace with more solder for good measure.

    [​IMG]
     
  9. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    With the amplifier powered on, have you tried gently tapping the PSU/Protection board with the blunt end of a screwdriver? and giving all the components a gentle nudge with something non-conductive? (- a chopstick for example?).

    This..
    And this...
    Are interesting, it rather suggests there is an issue on one of the driver boards - I assume you have multi-turn trimmers installed and this jittery DC offset effect only refers to one channel?
     
    Last edited: May 27, 2018
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  10. RR--

    RR-- Active Member

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    I haven't yet installed my new Bourns multi-turn trimmers as I'm still not sure of a neat way to do it, I bought trimmers where the adjustment screw sits on top rather than at a right angle, if installed I'm not sure how I could adjust it.
    The DC Offset adjustment issues seemed particularly bad on the left channel although the right was also very difficult to adjust.
    I have the day off today so I'll give it a go with a chopstick soon, thanks for the tip.
     
  11. RR--

    RR-- Active Member

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    So you may have found the culprit, I installed the Bourns DC Offset trimmer pots and set them, I accidentally broke a leg off the pot for the Bias so I haven't replaced those, they were never anywhere near as difficult to set though. Unfortunately the problem still persisted.

    I tried tapping various parts with a chopstick but didn't notice any changes until I tapped TR17 on the right channel driver board. Tapping it and bending it back and forth consistently triggered the protection circuit.
    The schematics lists TR17 as 2SC1845, would KSC1845 be a good equivalent I could replace it with?
    TR02, TR03, TR04, and TR05 appear to also be the same transistor so I'll replace them all while I'm at it.
     

     

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  12. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes! - that's what you're looking for!
    Yep, its exactly the same.
     
    Last edited: May 30, 2018
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  13. RR--

    RR-- Active Member

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    Thanks!
    So something interesting happened... I borrowed a KSC1845 from TR609 on the power amp board and swapped back in an old 2SC1313 transistor for the time being, I replaced the TR17 on the right driver board with the KSC1845 and the amplifier consistently powers on. Something wasn't right though because the resistor R635 on the power amp started to glow red hot and my house now smells like somethings burning. Whoops.

    I'll order some KSC1845's, should I now replace that resistor too? It looks ok now that it's cooled down but I'm not sure if I damaged it. It's Blue, White and Gold striped and thick but it's not listed in the schematics so not sure what specs it is.
    I'm not sure how it happened because that transistor was originally from there, funnily enough the protection circuit never tripped which is a step forward at least!
     
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes, do replace that resistor, swapping in a 2SC1313 may not have been a good idea - maybe the pin outs for a 2SC1313 are different?

    Update
    Pin outs not different but the voltage rating of 2SC1313 is just 50V - the 2SC/KSC1845 is 120V !!! - just because they look the same doesn't mean they are :)

    Very likely that 2SC1313 is toast now.

    R635, 68Ω is on the PSU/Protection PCB, it (and its friend R634) do get very hot, but should not burn. It is a current limiting resistor associated with the -ve 32.5V regulated supply, it is not clear to me why that should have got smoking hot arising from changing TR17. If I were you I would buy a few of those resistors - you may need them. ;)
     
    Last edited: May 30, 2018
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  15. RR--

    RR-- Active Member

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    Yeah probably not the best idea, although the 2SC1313 did originally come from TR609 so it's strange when it went back to the same place there was a problem. I got a bit excited with the thought of it working again haha.

    While you're here do you recommend any resistors to replace the two circled in this picture? I took this photo before some of their stripes burnt off haha.
    I'll add them to my order of transistors and hopefully have them by the end of the week. The cheapest way to get them is to order 200 from RS components so if anyone needs any let me know!

    [​IMG]
     
  16. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Yes, those are the ones, I'll have a look and see what I ordered for these last time I did an AU-719. Because they get so hot they discolour easily and look like they are on their last legs, but I found some resistors that don't discolour - I'll see if I can find what I ordered - I am sure I didn't need to order 200. :)
     
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  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Found it

    RS Stock No. 851-2693
    Mfr. Part No.PR01000106809JR500
    Brand Vishay

    These are 1W, 68Ω, 5% resistors - they are quite small but don't discolour - I was able to order just 10. ;)

    I have just been on the RS AU website

    You can get these
    Vishay PR01 Series Axial Metal Film Fixed Resistor 68Ω ±5% 1W ±250ppm/°C
    RS Stock No.683-5565
    Mfr. Part No.PR01000106809JA100
    Brand Vishay

    $0.253
    Each (In a Pack of 10)

    https://au.rs-online.com/web/c/pass...ors/?applied-dimensions=4293491270,4294869117

    Which seems to be the same thing.
     
    Last edited: May 30, 2018
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  18. RR--

    RR-- Active Member

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    Thanks very much John I'll add them to the order!
    The minimum quantity for KSC1845 from RS is 200, last time I bought them from mouser I spent over $60 for free shipping so it made sense, since I only need a couple things this time it's cheaper to buy 200 from RS, at least I'll have spares haha.
     
  19. Overundr1

    Overundr1 AK Subscriber Subscriber

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    If you are going to order those ksc1845's might as well order their compliment ksa992fbu's as well, You will find uses for them as well. No harm in ordering 60 pieces either, lets you get really selective with gain matching.
    -Lee
     
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  20. RR--

    RR-- Active Member

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    Damn the KSC992's only come in packs of 200 too, Mouser are out of stock of 1KSC845's too so it looks like RS is the only way to go.

    Also I realise now how I toasted that resistor, I borrowed a KSC1815 not an KSC1845, oh well it could have gone worse.
     

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