AU999......Big Job...

Discussion in 'Exclusively Sansui' started by kevzep, Aug 7, 2017.

  1. kevzep

    kevzep Its all about the Music Subscriber

    So, its started, I finally got the next AU999 on the bench and I spent an hour or so in the lab with it, started a bit of recapping and a few other bits as well as assessing its condition.

    This thing is a bit butchered up to be honest, it has had drivers replaced, some output transistors and I have found a couple of wiring errors, and these just looking at it and going from memory.

    My work has been cut out for me here, not sure how quickly this will progress, after repairing the Marconi 2018 520mhz RF generator, I seem to have a HP8675A RF generator on the bench now too, but the HP frizzed my brain, its complicated !! So I took a break to work on one of my favourite amps!!
    I also have a build going for restoring some Crown Macro-Techs, so a lot on, and there are a lot of concerts on over the next few weeks too which means long days for me and a lot of organizing, time is precious!!

    So there it is on the bench, and some of the bits I started pulling out of it....Someone has mounted a volume pot on the inside, left the OEM one in there, wired the new one up and just left it floating around in there, then there are wiring errors on the F1231 and F1277 boards, one of the bias transistors has been replaced with something less than ideal.
    I'm not actually sure this thing would have been working, but anyhow, I'm ripping into it and we'll make it sing again....:music:
    IMG_4796.JPG IMG_4798.JPG IMG_4799.JPG


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  2. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Hertfordshire, UK
    I am always amazed at the stuff people do and think is acceptable, as you say Kev, the amplifier almost certainly wasn't working, what the hell goes through people's minds to leave it in such a state :confused:

    It's definitely in good hands now, thank goodness. :thumbsup:
  3. kevzep

    kevzep Its all about the Music Subscriber

    Well thats right John, makes it more of a challenge.....I'll take some more pics, there's some brand X unmarked TO3 in one of the output slots, silly things like that....:yikes:
    It will turn out doubt about it....
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  4. skippy124

    skippy124 Super Member

    Sydney Australia
    Looks like there is plenty to keep you occupied!!

    Looking forward to more instalments

    Let me know if you need a bias transistor, I have a small stash of these (NOS).


    Last edited: Aug 7, 2017
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    BLAH BLAH AK Subscriber Subscriber

    Melbourne. ..Australia. ..
    :lurk:...Got a feeling this is going to be one of my favourite threads here....
  6. stereofun

    stereofun Super Member

    Tucson, AZ
    vacation or not - I ain't missing this one - Kevin if you need original drivers, I have a few laying around, but can't get to them before after the 16th - greeting from Paris
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  7. LBPete

    LBPete Rolling Along Subscriber

    Long Beach, CA
    Serial number? :D

    - Pete
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  8. Hipocrates

    Hipocrates Anti-Muppet

    Costa Rica
    Let's see how a 999 is reborn!
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  9. kevzep

    kevzep Its all about the Music Subscriber

    Yes there certainly is, and yes, wonderful, perhaps we can do a trade, I've got some TO3's from a G9000 that I don't need/prepared to part with.....

    yes I am going to head into the lab and do a bit more on this one shortly...

    It's already my favourite threads...:yikes:

    Oh wow, that might be the elegant solution I am looking for, thanks Tom that would be great.......I'll see how things progress..

    Roger that...:thumbsup:
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  10. Hipocrates

    Hipocrates Anti-Muppet

    Costa Rica
    Did I tell you about some modifications recommended for this units?:p
  11. kevzep

    kevzep Its all about the Music Subscriber

    Oh...really, do tell.....:idea:
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  12. kevzep

    kevzep Its all about the Music Subscriber

    Back in the Lab today with this AU999.
    Its pretty rough as stated earlier, however, its slowly but surely scrubbing up nicely. I'm just working through various things I can do before I put an order in for more caps, trimmers, resistors etc.....
    Would you believe I did not have one single resistor the right value for my own mods!! This will be sorted tomorrow post haste!!
    A few pics showing the journey today, you can see the brand X output transistor, the Sankens on one side, the left channel driver has had a lot of transistors replaced by some odd Sanyo TO220's.
    Yes I know, I go on about MJ15003's as an option for outputs, and you'll see I have MJ15024G's on there, and this is simply because I have a large stock of 15024/25 for the Crowns I work on, and they get the job done nicely too....
    Then there's this volume pot that looks like it might be the original which has been unmounted, the new one mounted but not wired up, I'll have to investigate and see what this is all about....
    I'm going to work on the driver boards tomorrow, have a think about the drivers and how this awful job someone has done mounting a new bias transistor can be tidied up...
    Did the plug in boards, got those all recapped and new transistors in, I had a bunch of transistors on hand strangely enough.
    The pile of bits removed is growing, and growing.....
    IMG_4813.JPG IMG_4814.JPG IMG_4815.JPG IMG_4819.JPG IMG_4821.JPG IMG_4823.JPG IMG_4824.JPG IMG_4825.JPG IMG_4826.JPG
    Last edited: Aug 8, 2017
  13. kevzep

    kevzep Its all about the Music Subscriber

    The growing pile of dodgy old parts coming out. Yes, I pulled the crowbar out, basically I didn't have those huge bipolar caps so I though meh, OUT it comes....
    I'll probably mount a new main bridge Rectifier tomorrow, get the driver boards done.....and the mods, there's an electronics hobby type shop not too far away from me so I will grab the resistors from there in the morning....
    I've been removing as much scum, oxidation and crap as I can along the way, its brightening up okay....
    And I am going to leave that note on the heatsink which was put there by a tech in 1979, I like it, he states the type of transistor he put in there, and the date, nice!!
    The traces n those PCB's are so very very delicate, they lift very easily, so you need to be careful, I use plenty of flux paste so I can get in and out very quickly.....
    So, I'll continue tomorrow....
    IMG_4827.JPG IMG_4828.JPG IMG_4829.JPG IMG_4834.JPG IMG_4835.JPG IMG_4836.JPG IMG_4838.JPG
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  14. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Hertfordshire, UK
    A nice thought to leave the label, thanks for posting the pictures, great to see now, and a great pictorial resource for someone else doing one later on. :thumbsup:

    Coming together very nicely by the looks of it. ;)
    Last edited: Aug 9, 2017
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  15. LBPete

    LBPete Rolling Along Subscriber

    Long Beach, CA
    It's looking good!
    I've seen this type of thing before in other equipment. Someone tries to graft in a generic volume pot. My best guess is the amp had channel drop out that would reconnect when the volume was increased. Higher volume will sometimes put enough voltage through a dirty switch or pot to allow the audio signal to pass through it. An uniformed person sees the relationship between the higher volume and audio output and assumes it's a bad volume pot.

    - Pete
  16. kevzep

    kevzep Its all about the Music Subscriber

    The two Pots are actually identical Alps, looks like someone has gone to all the trouble to find a NOS or New pot, then installed it but never finished the job, I'll test both and see where we are at.....but it does look to me now, like an unfinished job.

    Yes, I just couldn't bring myself to remove that sticker, it definitely has to stay.....

    So this is were we are at.

    All plug in boards recapped and new Transistors
    New Emitter resistors
    Filter boards recapped and new Transistors
    Regulated supply recapped
    High pass Filters removed
    Crow Bar removed
    New output Transistors
    Cleaned chassis as best as I could, plus all the steel covers ect.

    To do,
    Bass EQ Mod
    Pre-amp headroom mod
    Constant Current differential mod

    Recap and new transistors for the driver boards.

    New driver transistors, maybe MJ15033/32
    New Bias Transistors

    Put a new power plug on it!!

    I may look at some banana plug binding posts as well, I'll see what the owner wants to do.

    I'll check in later....


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  17. slimecity

    slimecity Super Member

    New Zealand
    Are you going to sell this one Kev?

    I'll keep an eye on trademe just out of interest!
  18. kevzep

    kevzep Its all about the Music Subscriber

    It's not mine, its for a customer, I'm not sure if he'll sell it or not, its possible, he already has one.....

    I'll let you know....
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  19. kevzep

    kevzep Its all about the Music Subscriber

    So I did all the mods and more yesterday, Bass EQ mod, Pre-amp mod, and another differential current mod.

    Neither of those bias transistors are correct, so I think what I will do is use a suitable TO92 replacement, but implement it in a more elegant fashion than the one you can see in the pic...

    I decided to use all new TO220 devices as the drivers, this unit is not exactly a museum piece, its cosmetically a bit average, if it was mint I'd be chasing NOS parts, but still, its going to sound as good as any AU999 out there.

    Just have to decide on some decent Main Filter caps, and fit a new Bridge Rec to go with the increased capacitance we'll have....
    Not as many pics today, I tried to clean the front panel as best I could.

    IMG_4841.JPG IMG_4842.JPG IMG_4843.JPG IMG_4844.JPG IMG_4845.JPG IMG_4846.JPG
  20. kevzep

    kevzep Its all about the Music Subscriber

    Well, I've pretty much finished this one, I have quite a bit of work on at the moment so couldn't take the time to go step by step.

    It runs up well and everything is nice and stable.

    I used some MPSA05 for the bias transistors, they seem to work well, they are a TO92, but I used heatshrink and insulated the legs to make it a bit nicer.

    I ran into an issue I didn't spot initially.

    Well, the muppets have been in this one too. Now we all know the AU999 uses a dual gang balance pot, and of course these have a special taper in order for them to work correctly.
    Well, someone has replaced it, not only with the wrong value, but completely the wrong taper.
    They also used too much heat soldering, and melted the internal insulation on one of the pot connections so one side was shorting out, so only one channel of the pre-amp was working.

    So I have come to a grinding halt on this until I can locate a suitable pot to replace the one that's in there.
    I know why this one was given up on, whichever muppet was fiddling with it, very quickly got out of their depth and gave up...

    There are a lot of new parts in this amp now, and its been a little bit frustrating working on it with some of the "gotcha" moments from the muppets, but all in all, they are really easy amps to work on, UNTIL you get into the wiring for the switches and pots, there were a few switches that were "rewired" for some odd reason...

    A few pictures of the journey....

    Its not going to be a museum piece, but it will perform as good as any AU999 out there once I get the balance pot installed if and when I find one.
    IMG_4896.JPG IMG_4897.JPG IMG_4899.JPG IMG_4900.JPG
    Last edited: Aug 26, 2017
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