AU-666: Strange behavior

KinjiroKiba

New Member
Hi All,

I've recapped my Sansui some times ago, and all was fine until now (good sound, both channels OK, no buzz, etc).

I am now facing a strange problem:
1) When I switch on the amp, everything is fine for a while. The sound is very good & clean.
2) Randomly (it can be 30min, 1h, 2h...), the right channel power disappear and the left channel becomes a lot stronger with a lot of noise (it is like right: -90% power & left: +90% power with hum, buzz...).
3) The only way to "reset" the amp is to switch it off, wait a while, turn the selector left and right, power it on: it works again until the randomly next time.

My first try was to clean the selector switch, but I did it twice or more and it has not changed anything.

Any thoughts on this?
 
The so called 'flying saucer transistors' can cause problems in these series, they look like this:

100_0909.jpg
 
Sounds like an earthing problem, cracked solder joint, or possibly a volume control losing a (ground) connection intermittently.

Try to get it to recover by a method other than powering off and on again - in other words, use a non conductive probe to gently push things until you get a reaction.
 
The so called 'flying saucer transistors' can cause problems in these series, they look like this:

100_0909.jpg

I have already replaced all the flying saucers, so they are innocents ;)

Hyperion said:
Sounds like an earthing problem, cracked solder joint, or possibly a volume control losing a (ground) connection intermittently.

I already try to check the solder joints, but no success!

Hyperion said:
Try to get it to recover by a method other than powering off and on again - in other words, use a non conductive probe to gently push things until you get a reaction.

Good idea! I will try this and I'll let you know if I can locate the source of the problem :yes:
 
I just tried to tap gently anywhere in the amp: no effect on the problem.

BUT I have noted that following the position of my hands around the amp, the regular hum in the noise is changing! Could it be a "bad" component open to electromagnetic interferences, which is reset after power off? Strange...
 
I just tried to tap gently anywhere in the amp: no effect on the problem.

BUT I have noted that following the position of my hands around the amp, the regular hum in the noise is changing! Could it be a "bad" component open to electromagnetic interferences, which is reset after power off? Strange...

Now try to use a wooden or plastic stick and push or press gently on things... (since tapping hasn't worked).
 
Last edited:
Now try to use a wooden or plastic stick and push or press gently on things... (since tapping hasn't worked).

Finally find it! It was just a capacitor with a bad solder on the tone board. I have located it following the "magnetic vibrations" in the speakers :D

I have reflowed the solder and everything is fine now!

Thanks you all for the advices :thmbsp:
 
Glad you got it resolved. I was going to guess that the problem stemmed from its being an AU-666 ...
 
It may wear 'the mark of the Beast', but it's still a Sansui! :D

Tell us more about the "magnetic vibration of the speakers" technique for finding the bad component/solder joint.
 
Back
Top Bottom