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Recapped Sansui AU-719 Protection mode help!

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

  1. RR--

    RR-- Active Member

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    I don't think so, I put them in the correct way for their pin out according to the picture in this thread: http://audiokarma.org/forums/index.php?threads/sx-780-transistors-oct-2016.739346/

    The puzzling thing is I tested the amplifier after installing these transistors the first time around and it worked great for several hours playing music. The protection issue was still an issue at this stage.

    The current problem can be narrowed down to when I accidentally put a KSC1815 where a KSC1845 should have gone in TR17 on the right channel.
    This caused the two resistors to burn out and continues to be a problem even when the incorrect transistor at TR17 has been corrected as well as the two burnt resistors.
     

     

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  2. RR--

    RR-- Active Member

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    New resistors in place
    [​IMG]
    [​IMG]
     
  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I'm really struggling to see how the TR17 event has anything to do with the present action in the negative regulator - my current thinking is that you are being mislead by a coincidence. KSC1815 and KSC1845 are very broadly equivalent except that '1815 has a higher current capability and the '1845 has the higher voltage capability - it will likely be this (voltage) that caused the issue with the wrong transistor situation.
     
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  4. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    R621 is surrounded by semiconductors - if it is burning, one or more of them must be faulty.

    R635 is a current limiting resistor placed where it is for exactly this kind of situation - it is a sacrificial part used to reduce the spread of damage during fault conditions.
     
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  5. RR--

    RR-- Active Member

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    247
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    That sounds like the problem isn't too bad then, what parts are semi conductors? I can measure them with my multimeter if possible.
     
  6. RR--

    RR-- Active Member

    Messages:
    247
    Location:
    Melbourne, Australia
    Also just to be clear here's the work that I've done recently:
    • D601 & D602 10D2 (1S2227) replaced with MUR240G Rectifiers 400V 2A
    • D607 10D1 replaced with MUR240G Rectifiers 400V 2A
    • ZD601 replaced with 1N5232B Zener Diode 5.6V 0.5W
    • ZD602 replaced with 1N5234C Zener Diode 6.2V 0.5W
    • SCR601 2SF656 replaced with MCR100-6A1G SCRs Silicon Controlled Rectifier with reversed pin order, SCR flipped
    • TR608, TR609, TR612 replaced 2SC1313, replace with KSC1815 (BCE to ECB, transistor flipped) replaced again after R
    • TR607, TR610, TR611 replaced 2SA726 with KSA992FBU (BCE to ECB, transistor flipped)
    • C615, C608, C612 and C613 replaced with new capacitors all in correct orientations.
    • R621, R622 replaced with new 100 ohm 0.5W 1% resistors.
    • R635, R634 replaced with new 68 ohm 1W 5% resistors
    • Also the blown 125V 7A fuse was replaced with a 250V 7A fuse, we have 240V power here in Australia.

    F-2926 and F-2927
    • VR01 3386P-1-101LF Bourns Through Hole 3/8IN 100 OHMS 10% 0.5Watts Square Trimmer Resistor and correctly set before burning began.
    • VD1212 replaced with two 1N4148's
    • C19, C20, C22 I02J 50 B_(N), WIMA 0.22uf 100 VDC 10% Film Capacitor
    • All 2SC1845 transistors replaced with KSC1845
    • All 2SC992 transistors replaced with KSC992
     
    Last edited: Jun 10, 2018

     

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  7. RR--

    RR-- Active Member

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    Also interesting, I've been going through all the original photos I took when I recapped this back in 2013 and I noticed I put a small 47uf 16v capacitor in backwards at C08 on the phono board, I put a new one back in according to how it came from the factory but it didn't fix the resistor smoking problem. It's funny because that capacitor hasn't been an issue and I've been using this amp daily since 2013. I don't listen to Vinyl very often though.
     
    Last edited: Jun 10, 2018
  8. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    That could well be relevant as it is on the -ve 32.5V regulated supply. - presumably C07 is the same - the + of the capacitor should go to the cathode of the associated zener - as shown on the schematic. The current pulled by those 2 reversed (and thus very leaky) capacitors could be enough to cause a problem - but of course should have stopped when you unplugged the phono power connector. A simple thing like a reversed capacitor will easily cause the R635 burning issue. - R621 burning is a different problem.

    BTW: you should never re-use a polarised electrolytic that has had reverse voltage applied.

    Semi-conductors are transistors and diodes - yes you can measure them with your multimeter - but sometimes such results particularly for transistors, are not conclusive - and only a transistor tester will show the fault if present.
     
    Last edited: Jun 10, 2018
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  9. RR--

    RR-- Active Member

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    I double checked and C07 is fitted correctly, I figured C08 would be toast so I put in the original 1979 47uf 16v I had still.
    I tried unplugging all three plugged in cables on the phono board and one on the EQ board again and the new R621 resistor still began to smoke.
    Any suggestions on what semiconductor transistors and diodes I should replace next?
    Thanks again for all the very specialist advice.
     
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  10. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    In the absence of any other information I think you should replace all the transistors in the -ve PSU i.e. TR610, TR611, TR612, TR613 - for new (never been used before) replacements - let's see if we can stop R621 burning at least. ;)
     
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  11. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    Clean every gap between the pads that you have soldered, just in case... You can use a piece of bamboo or a small screwdriver (gently)
    Are these on F-3101?
    I can see on the service manual that ZD601 is RD6.2E and ZD602 is RD13E

    I like to use BZX 2% types
     
    Last edited: Jun 10, 2018
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  12. RR--

    RR-- Active Member

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    Yep these are already installed on the power supply/protection board, think that could be causing some problems?
    Thanks for the recommendation, if it's no trouble could you link to some suitable replacements? I'm obviously not the best at picking them haha.

    Thanks I'll replace those soon and report back.
     
  13. RR--

    RR-- Active Member

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    Location:
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    Also I'm not completely confident with something here and would like to double check with you.
    2SC1313 and 2SC726 are BCE, that means putting in the equivalent transistors KSC1815YTA (BJT NPN) and KSA992FBU (BJT PNP) respectively flipped 180 degrees should be correct right? Or have I put one in backwards by mistake?
    The new transistors in positions TR607, TR608, TR609, TR610, TR611, TR612 and the SCR have all had their orientations reversed.

    https://au.mouser.com/ProductDetail/512-KSA992FBU
    https://au.mouser.com/ProductDetail/512-KSC1815YTA

    Photos here: (The after photo was taken before TR612 was replaced)
    Before: https://i.imgur.com/O8NaTe4.jpg
    After: https://i.imgur.com/ma0qh1r.jpg
     
  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Looks OK to me - I checked your thinking on the orientation of the transistors - all ok.
     
    Last edited: Jun 12, 2018
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  15. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    RR-- and Hyperion like this.
  16. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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  17. RR--

    RR-- Active Member

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    Yep, just double checked and it's an 1815 in TR612, it's orientation has been reversed too.
    Thanks
     
  18. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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  19. RR--

    RR-- Active Member

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    Unfortunately that photo was taken before I had installed that transistor but nice observation regardless.
     
  20. Hipocrates

    Hipocrates Anti-Muppet Subscriber

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    It's ok, just checking.
     

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