Yamaha amp CA400 hissing

[pletevl]

Hi all,

My YAMAHA CA400 amp has started hissing on the left chanel on all sources. It isn't lound and it doesn't change with the volume control. Even with the volume on zero, it hisses.
The sound and volume is fine, no other problems, just this left chanel hiss.

Any ideas ?

Thanks

Pete.

[Silicon]

Faulty transistors or integrated circuits can introduce a hissing noise.

The faulty transistor / IC can sometimes be identified by spraying it with a 'freezer' spray.

[tri-comp]

Originally Posted by Silicon

The faulty transistor / IC can sometimes be identified by spraying it with a 'freezer' spray.

Sparringly spraying on top of transistors, one at the time, allowing for the freeze-spray to evaporate and cool down the item, before moving on to the next, may very well send the culprit out in the open.
I would start out with transistors TR705/TR707 or TR706/TR708 (all 2SA763WL) according to channel, as they are the most likely to introduce this kind of noise.
Keep a hand on the power-switch when spraying.
I've seen violent reactions to freeze-spray on partially defective semiconductors.
This amplifier has NO speaker protection-circuit. If any of the mentioned transistors should decide to go bang during the freeze-test, so will your speakers.
Use a headphone during the test instead as at least it will be in series with a 270-Ohm resistor from the speaker-terminals.
If inded you track the fault to any or more of the mentioned transistors I would replace all of them.
-
There's a so-so quality schematic diagram of this amplifier circulating the web. If you would like a higher quality specimen, send me a PM with your e-mail address. Be sure your mail-box will recieve an attachment around 13Mb in size.

Rgds,

/Torben

[pletevl]

Torben. You seem to know this amp. Pm sent with my email address. Thank you.
Pete.