Hurt my AU-717 (current went wrong way, channel dead )

Discussion in 'Exclusively Sansui' started by delboyko, Dec 28, 2017.

  1. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Well, I ran a quick check and here are the results.

    Nonworking driver: C01 (capacitance: unmeasurable; Resistance 0,5 ohm)
    Working driver: C01 (Capacitance: 160 pf; Resistance: unmeasurable)

    Everything measured on PCB.
     

     

    Please register to disable this ad.

  2. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
    uk.. the middle bit
    you need to remove it and test again .
     
  3. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    Mine in circuit using two different dmm c01 resistance 57k, capacitance unmeasurable. My equipment will not read cap in circuit.
     
  4. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
    Caution, if you remove that cap, put a heat sink on the leads or you will cook it!
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
    uk.. the middle bit
    think its already cooked by the looks of things
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
    uk.. the middle bit
    is it a styrene cap ?
     

     

    Please register to disable this ad.

  7. Bigdrive

    Bigdrive Member

    Messages:
    98
    Location:
    Kelowna
  8. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
    uk.. the middle bit
    only ever seen one of those short .was signal path in a valve guitar amp . this night be the second one i have known about . if you dont want to remove it lift one end of R02 and test again . this leaves the cap and the fet . but resistances dont add up if fet shorted
     
  9. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Removed the R02 leg and measured again:

    C01 Capacitance: unmeasurable; Resistance 0,5 ohm. Hope it's the only thing wrong.
    Should I go with a PP or C0G cap?
     
    Last edited: Jan 13, 2018
  10. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    43,783
    Location:
    Hertfordshire, UK
    Last edited: Jan 13, 2018
  11. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Croatia (EU). Mouser was choice but smallest they have is 150pF
     

     

    Please register to disable this ad.

  12. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    43,783
    Location:
    Hertfordshire, UK
  13. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    I'll search around, although I doubt it.

    Still have to find the culprit on power supply board.
     
  14. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Many thanks to all the folks in here, especially @petehall347 !
    Replaced the C01 (100pf) with the first ceramic cap I could find and it plays loud and clear now. (will replace that with polystyrene as soon as I get my hands on one)

    Unfortunately still no luck with power supply board. Took it out yesterday to get a better look at it and checked all the transistors, diodes and caps(First without desoldering). Almost everything turned out fine and within spec. Those few things that I couldn't measure right I removed afterward.

    First thing I tried is to check the continuity between 28 & 30 and 29 & 27. Let me remind you, 28 is the wire that I found to be the culprit. I can get both channels to play just not at the same time. When I take 27 and plug it in the driver board (in the place of 28) I get it to play just fine. Could this mean that speaker relay is bad on one channel? How could I check this one for sure?

    (28 = brown; 27 = orange; 30 = green; 29 = pinkish)
    [​IMG]

    Ohmmeter showed no connection between 28 & 30 and a fluctuating high resistance(15-30k ohm) between 29 & 31. This was measured with amplifier with PCB still in the amp...

    All diodes were ok except for D605 & D608 which lead current in both ways. So I removed them and they turned out to be OK. All fuses are OK, all zeners are OK.
    I've removed a few caps that could not get a stable measurement on my meter, and again all within spec.
    [​IMG]

    Is it possible that it's the speaker relay? Visually all the leads look perfect. It's replaced in the recap process with an Omron unit.
    ps. It doesn't help if I turn the volume up, and the relay makes a normal spring sound.
     
    Last edited: Jan 21, 2018
  15. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
    uk.. the middle bit
    relay or wiring to speaker terminals
     
  16. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,459
    Location:
    Mississippi
    Remove brown and orange wires from amplifier cards.
    Set multimeter to ac volts.
    Connect from orange pin to one meter lead the other meter lead to ground

    Start with volume at zero output with some sort of music source and slowly increase watchimg to see if ac voltage rises. Stop if you reach 1 volt for now.
    Repeat with brown wire.
    Report back :)
     

     

    Please register to disable this ad.

  17. Overundr1

    Overundr1 AK Subscriber Subscriber

    Messages:
    2,459
    Location:
    Mississippi
    Those relay contacts dont look too good in your picture above
     
  18. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    Well, I don't know where to start from... probably from the fact that both channels play now. But only if I separate preamp and plug source into "main in". :D

    Well, I've tried this before all the fixes and I had crossed out the preamp and power supply because I had to start from the obvious. After fixing the bad driver, I knew there was something with the PS because, well... ti didn't work. With your help, I've narrowed it to relay. Although I've been suspicious about this one I've resoldered the original relay and returned everything in the box. Turned it on, relay clicks and again just one channel, and again the one that is playing well from the beginning of this saga.

    I knew that best thing I could do is to check is it going to play without preamp, and it did, sweet and powerful as always. :beerchug:

    I've checked the voltages on the corners of PS board and results were different. One gave 36V and other 24V. I thought, to hell with it! I've either managed the impossible and fried all 3 components of one channel or damaged something in the process while replacing the relay. Doesn't matter, it can wait for tomorrow because I've earned my self a listening session.

    And so, while listening to the "fortunate son" and admiring the top view of my 717, I've got my head closer to the amp to hear its heartbeat.... and literally, I've heard it! :crazy:
    Thinking to my self, it's getting late and I've better go to bed I see this cap bugger popping bubbles. :beatnik:

    There...I've got a pic for you:
    [​IMG]

    Why and how? don't know, don't care anymore. I'll replace it and hopefully get a preamp to work again. I've checked the voltages on the preamp section of PS without the connection to the preamp itself and both channels return around 19V so I guess that's fine.

    While having you good folks here I've got a few questions more if you don't mind...
    I'm just curious, how do I set my bias and DC offset with this scenario? Now it looks like: Chromecast audio --> DAC --> Sansui. I have volume control digitally maintained over chromecast and when I stop the music and read the BIAS I've set the offset to 0.This does not change with the digital volume. However, when I turn off the DAC offset jumps to 30mV. Should I set offset with DAC on or off?

    Just one more thing I've got to add here... Listening to my favorites without preamp sounds noticeably better; more present and live voices, more details... What could be the cause of this on the preamp board? Everything recapped as per leestereo's recipe. Also, the hum is less audible now, although you can hear it only with your ear next to the speakers.

    Thank you, good folks, once again for bearing with me.
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    25,711
    Location:
    uk.. the middle bit
    offset and bias is set with no inputs and vol to min . selector on aux .
     
  20. delboyko

    delboyko New Member

    Messages:
    19
    Location:
    Croatia
    So you're advising that I disconnect the DAC from "main in" and proceed setting bias and offset with amp in this setup? Correct me if I'm wrong but selector and volume do not play a role in this configuration.
     

Share This Page