problem with my 999

Discussion in 'Exclusively Sansui' started by stevestadler, Jul 24, 2016.

  1. kevzep

    kevzep Its all about the Music Subscriber

    Yeah, I just opened up my first of two AU999's I am working on, and it indeed has those diodes, they wont cause any issue with blowing rail fuses...
     
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  2. kevzep

    kevzep Its all about the Music Subscriber

    Have you tried all the things we have suggested?
    You need to be methodical and work through this logically, just putting things back in and taking them out and giving us little information about what you are doing and what has been done is making it hard for us to help you.

    The subsonic filter will have nothing to do with the problem.
    The crowbar has absolutely NO effect on the sound of the amp, it simply is triggered when there is excess DC on the speaker outputs and blows the quick acting speaker fuses.

    We need to go back to the beginning and with the original fault, and start again.

    Do not pull things out and put things back in until we tell you to, otherwise we wont know where we are at....

    So tell us in bullet points, what is exactly happening now.
     
  3. stevestadler

    stevestadler New Member

    Messages:
    48
    I would like to start by apologise kevzep, I'm trying so much then sometime I didn't make the right decision
    starting now I'm only listening to you
    I just reinstall the amps the way it was after your post, and yes I did everything you tell me to try with unfortunately the same result
    I will not touch the amps other then what you tell me to do, I'm just getting so frustrated, so what I'm going to do is put the amps aside until you tell me to try something else and work on my 7700
    sorry again I didn't want to upset anybody

    by the way I'm French, so sorry for my writing

    I found something yesterday, I don't know if its really important but I don't want you to miss anything, its about the power on the 1230 board, od-oe-of I only get about 8.4 volt
    on each, but og and oh give me -36 volt
     
  4. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,070
    Location:
    Costa Rica
    Bonsoir Steve
    Those 999 are the work of the devil!!!!
    Just kidding.

    I understand your frustration, I have a love/hate relationship with the 999, specially because everybody says that is a very simple amp to work with. Just be patient, this guys knows their stuff and I'm sure they will lead you to a great outcome.
     
  5. stevestadler

    stevestadler New Member

    Messages:
    48
    thanks, I'm really closed to depression haha
     
  6. Hipocrates

    Hipocrates Anti-Muppet Subscriber

    Messages:
    1,070
    Location:
    Costa Rica
    I know the feeling:smoke:
     
  7. kevzep

    kevzep Its all about the Music Subscriber

    Later this afternoon I will come up with a plan to start diagnosing this, your English is perfectly fine...
    I can understand everything you are saying...

    We will start at the output transistors, work back through the driver transistors and into the driver boards.

    We know the emitter resistor on TR818 is heating up so there is a lot of current running through TR818, so we need to find out why, eliminate where the fault is and move forward from there.

    Really, these amps are so easy, I love working on them......We will get you going...

    One thing first, can I get you to check TR809 which is the bias transistor which is clipped to the heatsink, make sure the transistor is OK, and connected correctly, make sure none of the legs are broken, be careful with them...

    Where is the Bias trimmer set? Have you changed it at all?
     
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  8. stevestadler

    stevestadler New Member

    Messages:
    48
    tr809 are ok I replace them because the old one were dead, I found two in England
    and unfortunately I touch to clean and check them, I put those in the middle
     
  9. stevestadler

    stevestadler New Member

    Messages:
    48
    sorry the bias trimmer are set in the middle
     
  10. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,499
    Location:
    uk.. the middle bit
    i did wonder where bias was set myself ..carry on the good work work folks ... p.s they need turning down first . best done on dbt .hopefully bulb will go out .
    some turn down clockwise .others anticlockwise .. wait for kev to give clarify this .
     
  11. stevestadler

    stevestadler New Member

    Messages:
    48
    thanks you, just waiting for kev
     
  12. kevzep

    kevzep Its all about the Music Subscriber

    LOL....Just adjusted the bias on one not two days ago, I can't remember....Hahahaha...It could go the opposite way....:idea: they often do on Sansui's, the G9000, 22,33K all go the opposite way...

    Perhaps someone else can remember, in the meantime I can suggest perhaps clip your DMM over one of the emitter resistors, and turn it on, (on the DBT) and see if you can adjust it down to between 10-14mV (DC). Hopefully you have an auto-ranging multi-meter so if its high you'll still get a reading...
    If you adjust it and nothing changes, shut it down quickly...
    You wont have much time before things start heating up, so be quick, set yourself up so you are ready with everything before you flick the switch.
    Clip you leads onto the Emitter resistor etc etc, get the amp in a position where you can easily get to the bias trimmer.
    If you turn it on and the voltage over the emitter resistor shoots up over 2VDC or something, then you have a dead short, so shut it down immediately.

    Let us know how you go...
     
  13. stereofun

    stereofun AK Subscriber Subscriber

    Messages:
    1,079
    Location:
    Tucson, AZ
    I just checked the old trimmers I pulled from my 999 rebuild. When facing the trimmer, that is adjustment screw toward you, - turning it fully counter clockwise will yield the least resistance and fully clockwise the maximum resistance. If I remember....then the bias circuit is designed so that the more clockwise you turn (higher resistance) , the higher bias you get. As for the DC- offset, I'd start in center position, and just quickly dial toward zero DC.

    You can also measure on the first two legs (left to right), this will give you the current setting. If then Kevzep has som values you can duplicate, - then at least you will start off in the ballpark range.

    These trimmers are a weak point and really should be replaced sooner or later. But as to verify for now, you should confirm their total resistance pr. service manual by probing on the outer two legs (1,3) , then next, by probing on leg 1,2 and turning the screw to see if they are "smooth" within their range. If not, I'd replace them first because they could keep on triggering the amp to either overheat or shut down pr. Protection circuit.
     
    Last edited: Jul 30, 2016
  14. stevestadler

    stevestadler New Member

    Messages:
    48
    ok something very strange happen today, I can start the amp with the 1159 insert no problem no smoking, everything seem ok that side???
    I was able set the bias at 0.010mv
    now the fuse blow on the left side, even with the lightbulb, everything ok if I remove the positive fuse
    I have no idea what happened, I didn't touch the amp
     
  15. stevestadler

    stevestadler New Member

    Messages:
    48
    I did some voltage check, both 50v/4700 power drop to about 4 volt when a power up with the 1159 insert
     
  16. kevzep

    kevzep Its all about the Music Subscriber

    Okay, so with only ONE driver board, you say you could set the bias? It should be around 10mV or 0.010V

    So now the fuse will blow with the OTHER driver board in? Is this correct?

    There will be some voltage drop when the driver boards are in naturally as they will load the supply a bit....
     
    Last edited: Jul 31, 2016
  17. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Messages:
    39,475
    Location:
    Hertfordshire, UK
    Tiny little typo there 10mV = 0.010V :thumbsup:
     
    Last edited: Jul 31, 2016
    kevzep likes this.
  18. stevestadler

    stevestadler New Member

    Messages:
    48
    yes, at the beginning the dim bulb didn't light up, after changing the fused 3 time, suddenly the dim bulb start working so no more blowing fused

    I was able to set the bias at 10 mv

    now the positive rail on the left side light up (dim bulb) when the 1159 is insert on the right channel
     
  19. kevzep

    kevzep Its all about the Music Subscriber

    Okay, this is good progress!!

    This 1159 board which causes the Dim Bulb to light up has either a blown transistor, diode, OR it has a transistor mounted incorrectly, OR a PNP where there should be a NPN.
    Have you tried to set the bias on this board?
     
  20. stevestadler

    stevestadler New Member

    Messages:
    48
    unfortunately the light go on to without the board insert left channel
    do you mean the problem will be on the 1159 on the write channel, sorry I want to make sure?
     

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