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Sansui AU-222 advice please

ZanzibarMDS

ZanzibarMDS

New Member
I’ve got an AU-222 which has an issue with the left channel.



Music can be heard out of both channels but there is a major sizzle sort of sound. A cross between bacon sizzling in a pan and fireworks. Definitely unusable and potentially speaker damaging so at this point I continued testing with cheap headphones.



With both left and right fuses in

- music and noise.



With only left fuse in

-music and noise in left channel only.



With only right fuse in-

music but without noise in right channel only.



I next went through the schematic (F-1082) and measured all the noted test voltage points on the left and right sides. I have the readings and can post them if that helps. What I did notice was that the right channel side, while some of the readings were a bit out, the volts were steady on my multimeter where on the left channel side they seemed steady at TR801 collector and emitter but from TR803 onwards the volt readings were fluctuating quite a lot.

I also noticed this fluctuation when checking current bias on the left channel.



The amp has all the original components. I have cleaned and lubricated all the pots and switches.



I’m hoping someone can assist me with diagnosing the issue and get this awesome little amp up and running again.


Any help would be much appreciated

Mark
 
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Below are some photos of the circuit board from both sides, the schematic where I measured the test voltages and the measurements.
 

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bolero said:

Top Ten Worst Transistors - noisy, failure-prone, whatever... and replacements

I've followed AK advice for several vintage solid state receivers now and the difference in sound, from recapping and from replacing "known-to-be-noisy" small signal transistors to be amazing. While following along with others' threads and trying to help out with "consider replacing these...
audiokarma.org
Click to expand...
Hey Bolero, thanks very much for the reply. So with your experience you think it may be a defective Transistor? I will read through the thread you attached and it may be a great place to start.
Thanks again

Also if anyone else has any suggestions it would be nice to hear them.
I would eventually like to replace all out of spec components but would first like to address this issue first
 
bolero said:
I had a quick look at the schem & my bet is on the 2SC871's but there may be others?

your symptoms sound exactly like bad transistors
Click to expand...

That was a great idea on the video link you sent where the guy solders a 10 ohm resistor between the base and emitter on the suspect transistors to see if the noise disappears.

I could try that technique first on the 2SC871's you suspect.

Also would bad transistors explain the volts fluctuating at the test points on the left channel?

Thanks
 
Also another thing I forgot to mention in the original post is that the noise is there regardless of the position of the volume.
 
The transistors finally arrived and have had a win with the AU-222.

In Bolero’s comment, he posted a link to ‘Top ten worst transistors’ In that thread there was a video where a guy temp soldered a 10 ohm resistor across B & E to diagnose a the noisy transistors. Below is the link to that video.


So when I did this on transistor TR802 the noise disappeared.

I then replaced this transistor 2sc871 with a new transistor KSA1845 which was exactly in line with what quadmatrix suggested.
Powered up the AU-222 and the noise has disappeared.

I also replaced the corresponding transistor TR801 on the other channel as a precaution.

There are another four of these problematic transistors which look to be a little harder to get to. Would you guys recommend changing these as well?

The sound coming out of this tiny amp is just unbelievable, very engaging and I can’t stop listening to it.

Once again thanks for the help

Mark
 
Congrats. I'd finish the job. Wonderful little amp, my daily driver in my office.


Edit: then again if you're not doing a full recap it can wait for another time, enjoy it now. It's not like this amp is hard to open up and work on
 
Last edited:
bhairavi said:
Congrats. I'd finish the job. Wonderful little amp, my daily driver in my office.


Edit: then again if you're not doing a full recap it can wait for another time, enjoy it now. It's not like this amp is hard to open up and work on
Click to expand...
Yeah thanks,
And good advice to enjoy it for now.
I think it has just become my favorite amp
 
If you have the skills you can do the adjustments in the manual for bias and centre voltage as well there’s some threads here how to do it also bear in mind safety here
 
quadmatrix82 said:
If you have the skills you can do the adjustments in the manual for bias and centre voltage as well there’s some threads here how to do it also bear in mind safety here
Click to expand...
Yeah good idea, I should do an alignment on it. I’ve got the online service manual. The trim pots look a little deteriorated though.
 
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