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Sansui au222 bias adjustment issues and crackling

zeste

zeste

New Member
Hello,

I have recap my sansui au222, replaced the 2sc871 with bc550c, and the trim pots.
I set the bias ajustment at 20mA.

It woks fine for a couple of month. And it started crackling and sound being fuzzy.

I replaced some resistances(the 0,5 ohm 2w and others) but nothing change. Then I replaced the 2sc815 and 2sa539 by new one.

It is better but I can set the bias. What ever I do, the bias is at 11mA max.

I don't known what to do. Can someone help me ?
 
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Since everything was working okay after the recap, as a first step I would go around and check all solder joints.
 
Thank you for you advise, yesterday, I started checking all the electrical voltage that are in the schemes, and I accidentely find that a pin of 2sa539 was mouving. So I check the solder and I re do the solder of this transistor and now the sound is very clear :)

For the bias, some people advise me to che k it after one hour of running. I am going to do it in the comming days.
 
zeste said:
Thank you for you advise, yesterday, I started checking all the electrical voltage that are in the schemes, and I accidentely find that a pin of 2sa539 was mouving. So I check the solder and I re do the solder of this transistor and now the sound is very clear :)

For the bias, some people advise me to che k it after one hour of running. I am going to do it in the comming days.
Click to expand...

Great. Yeah, something like that is the usual thing if you have troubles after a restore that is working fine for a while.

Regarding the bias, the AU-222 doesn't run hot. 5 minutes should be sufficient waiting time before biasing up. If you can't bias up to spec pretty much straight away, there is probably an issue to resolve.
 
smurfer77 said:
PS. A wonderful little amp! Sounds better than most of the bigger ones IMO.
Click to expand...

Yes one of my prefered amp, 18W sounds like it has much more and the sound is very musical (I don't know if you say like that in English) and very rich.

The Fuxtor said:
Make sure to check the centre voltage too...
(Center??)
Click to expand...
I have done it after recaping and I have checked it when I 've got the problem, and everything is OK.

When it's not set correctly the sound is not good or poor.

After recaping :

http://www.hostingpics.net/viewer.php?id=762814AU222N6.jpg
 
After a while, I get a new AU222 with 2SC1030 that I have restored. And I've got the same issues.

I found why I can't set the bias correctly. I have replaced the 2 diodes D801 and 802 on both AU222. So I decide to check these diodes with a RLC tester . And the surprise is that forward voltage is not 0.6V but 1.37V

HeZ5CjZ.jpg


So I decide to put back the old diode and then I was able to set the bias correctly :-) !!!

Here is some pics a the restoration :
e5U6gGM.jpg


hUKUkPO.jpg


6uSSt6B.jpg
 
zeste said:
And the surprise is that forward voltage is not 0.6V but 1.37V
Click to expand...
That's because it's a 'dual' diode - with 2 diode junctions inside the 'little boat' encapsulation. Replacing it with a single diode really messes things up - as you discovered. :)
The Fuxtor said:
Make sure to check the centre voltage too... (Center??)
Click to expand...
Yes, we say 'centre' you say 'center' - it sounds the same when we say either - but over there you spell it incorrectly. :D
 
Very nice work, I'm waiting on a 222 in the mail that I've recently bought. Another upgrade you could do for long-term reliability and stable performance is replace the original trim pots for sealed multi turns, first thing I'll do with mine. Enjoy.
 
Hyperion said:
That's because it's a 'dual' diode - with 2 diode junctions inside the 'little boat' encapsulation. Replacing it with a single diode really messes things up - as you discovered. :)
Yes, we say 'centre' you say 'center' - it sounds the same when we say either - but over there you spell it incorrectly. :D
Click to expand...
I'm in Canada! We use both spellings but there have different applications...
Centre as in the city centre or center as in the middle...
I ruined our own rules!!:rolleyes:
 
I didn't change the trim pot because I don't have noise or hum at low volume and when I have done the adjustment with them, I didn't have the value jumping.

Hyperion said:
Yes, we say 'centre' you say 'center' - it sounds the same when we say either - but over there you spell it incorrectly. :D
Click to expand...

Yes I've done it with my oscilloscope. After the recaping and changing the 2SC871, the au222 sounds awfull. After setting the center point, the au222 sound like it should !!!
 
I'm a total novice with an AU222 that I'm looking to restore and I'm gathering as much knowledge as I can, before starting.
The amp works very well, but I've got the distant bacon frying in the speakers, which I'm suspecting is the 871's transistors and i plan to replace them all.

After which, I was planning to set bias with oscilloscope as per manual but...
Just wondering what this 'centre' is, that's being referred to, in this thread?

Hope there's someone still here, who knows
 
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