Small job on AU999, BIG job on AU-X1

ghazzer said:
I admire your stamina for being able to work on this for hours at a time, until you get it done. I am too easily distracted, and too easily frustrated when things don't always work out as planned.

Never the less, successfully rescuing one of these beauties is quite rewarding no matter how long it takes. Thanks for the pics and your narrative.

Enjoy - - -
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Thanks, its not always plain sailing, but it does take a certain mind set, sometimes you have to get creative...if you want to check out my recent journey, have a look at this one in the pioneer forum, once you've been through it you'll see how well Sansui actually built their amps.
That Pioneer does sound amazing though......http://audiokarma.org/forums/index.php?threads/sx1980-power-supply-board-oh-noooooooo.770852/

Overundr1 said:
Bench edge multi angle vise envy over here, dangnabbit another goodie to add as that looks more sturdy than the large helping hands stand I use now. Also, I recently switched lighting over my own bench and the rest of the shop to led 4' lighting fixtures, far better than florescent tubes, seems to be less shadowing of the work area. Might also add grumble grumble about folks that repair loose knobs on expensive components by using epoxy to attach them to the shaft geez :(
Looks like the total parts count for the restoration will rival some of the big quad receivers.
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Oh yes that vise is really good, especially if you can completely remove the board you're working on and mount it in there, I did those MC head amp and flat amp board in that, makes it so easy....
LED lighting is pretty good, but I almost exclusively use an optivisor with 5 and 10x magnification (helpful for my tired eyes) it also has an LED lamp on the front, its really good.
I'd also be lost without my Hako solder pump too, that also makes looking after those fragile boards a lot easier....
Later today I'll be back on this project....
 
kevzep said:
Thanks, its not always plain sailing, but it does take a certain mind set, sometimes you have to get creative...if you want to check out my recent journey, have a look at this one in the pioneer forum, once you've been through it you'll see how well Sansui actually built their amps.
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I have never figured out why Pioneer with all that engineering talent set up most of their power supplies to run so darn toasty. Another point in the Sansui brand's favor is actually leaving enough wiring between boards that were not coupled with molex to actually get the board out for repair in most cases.
 
Overundr1 said:
I have never figured out why Pioneer with all that engineering talent set up most of their power supplies to run so darn toasty. Another point in the Sansui brand's favor is actually leaving enough wiring between boards that were not coupled with molex to actually get the board out for repair in most cases.
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Yeah you gotta ask that question, yes options were limited as far as regulated supplies went back in those days, but Sansui really did lead the charge on design in that department...
 
kevzep said:
Yeah you gotta ask that question, yes options were limited as far as regulated supplies went back in those days, but Sansui really did lead the charge on design in that department...
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The engineers/groups must have been fairly compartmentalized? Notice how pioneer made great turntables and r2r, kenwood some amazing tuners, and so on. (this is not to say neither of those brand made no good amps etc). On the other hand, Sansui (mostly) failed in mechanical efforts (particularly with r2r and cassette at least (a sansui tape engineer told me as much earlier this month)).
 
restorer-john said:
I love your kettle dummy loads- very inventive! 2400W each, 24ohms, three in parallel is 8 ohms.

They will even turn off when the water boils. :)
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Absolutely, I have to do full load tests on those Crown Macro-tech 5002's in the background there as they run at full power most of their lives, was the best cost effective solution I could think of....The sales lady in the store was wondering what on earth I was doing with a Multimeter measuring the Kettles, was a humorous situation...but was happy when I said, I"ll take four please"......
 
Overundr1 said:
I have never figured out why Pioneer with all that engineering talent set up most of their power supplies to run so darn toasty.
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Your idea of a hot bjt and its long term reliability is based on I believe to be your finger test and not solid engineering per se. Yes the cooler they run the better but then again as long as there is sufficient margins as far as die temperature goes, they could last decades, as has be shown, many are still running fine today.
We know they could have done better on say the 1010 and the 1980 but they made decisions also based on economics as well.

Kevzep, for that 70Hz HPF, you could modify it to make it act more like a rumble filter , something in the 15-20 Hz range would be more suitable. It can be simulated in ltspice to verify the design.
 
Very true RC, and yes to components running hot yet well within their s.o.a. Just bugs me when there are so many thermal solutions available to allow for high current draw on bjt's yet maintain lower thermal values.
 
rcs16 said:
Your idea of a hot bjt and its long term reliability is based on I believe to be your finger test and not solid engineering per se. Yes the cooler they run the better but then again as long as there is sufficient margins as far as die temperature goes, they could last decades, as has be shown, many are still running fine today.
We know they could have done better on say the 1010 and the 1980 but they made decisions also based on economics as well.

Kevzep, for that 70Hz HPF, you could modify it to make it act more like a rumble filter , something in the 15-20 Hz range would be more suitable. It can be simulated in ltspice to verify the design.
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On the SX1980 I restored, the 13.5V regulator, even after I put a larger heatsink on it was running at 70˚C (close to 160˚F).....I even put a higher value voltage drop resistor (22Ω rather than 10Ω). Thats too hot in my book.
We accept some heat will be generated and thats fine, but in this case, its simply too hot, the reliability and scorching of the AWR154 tells its own story....

Yes your idea of making that sub sonic filter into a rumble/HPF is actually quite a good one, as I don't think the AU999 has one....Not sure where you'd mount a switch though....food for thought...
 
There's no doubt in my mind that once a component scorches a PCB in 'normal' operation, the component, and its heat management system is inadequate.

Sure, we all know BJTs can happily run at 110degrees C above ambient 24/7, but the capacitors 2mm away from them, the PCB material and the solder itself can't tolerate that long term.

70degrees Celsius on PCB mounted components is my cutoff for bad design. That includes resistors hard down on a PCB, TO-220s either on, or not mounted on a small fin heatsink, 78xx regulators, driver transistors in amp stages and other linear regulators or voltage dropping daisy chains.

I've come across many CD players with completely sealed cabinets that have local regulators, non-heatsinked, running at 95+ degrees C, cooking themselves and surrounding components. In their hurry to get products to market, decisions on thermal management were clearly not considered.
 
Anyway back to this X1 and the bazillion capacitors it has!! Not really much to see at the moment, just working on this power supply board, caps caps and more caps....large heatsinks on those regs, wondering how hot they run or whether they are enough to keep the regs under control and to a reasonable temp...
Looks like there's some diodes to replace on this board too.
Man that glue is awful, this is the worst I've seen, its really hard to get off, and I scrape it off, I know some of you will do it differently and use powerful solvents, but I am a health freak, and I refuse to inhale those sort of fumes, soldering is bad enough....But the glue has to come off and that's how I do it...Some of the glue has crystallized so I really concentrate on those areas as I believe that's when it becomes corrosive....I had to remove a few resistors to get to it in some cases, once I have these front boards done we'll move inside the chassis and work in those areas.....
IMG_4685.JPG
 
Tight quarters for sure, that's where one dropped cap lead when clipping them off will drive you crazy trying to find where it ran off and hid.
 
Overundr1 said:
Oh be brave sir :)
Sing along---
Nothing to do, nothing to do, I know lets have fun removing Sansui glue
Sorry, could not resist, beats doing those 100lb arm curls wrestling around the MC2200 currently occupying my bench.
-Lee
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Hahahaha, yes well those Mc's are hugely heavy!! That was the worst of the glue......
 
Hyperion said:
My flush cutters have a little 'fence' that traps the cut lead preventing it from 'escaping' ;)
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I tried a lovely Japanese pair with the 'fence' but just couldn't get used to them. I use my fore-finger pressed into the upper side of the jaws for even the shortest leads and it catches 99.99% of them. (yes there is always one...). Bonus is the tiny cutoffs stay 'stuck' to your finger and can be dumped in the pig-tail dish.

example.JPG

As you can see, the forefinger gets used to being a pin cushion and toughens up...:)
 
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