Yamaha RX-385 started hissing

[thespinnerboy]

My Yamaha RX-385 started hissing, even with the volume at minimum. I turned off the speakers and listened with headphones - still hisses. I unplugged all the input cables and the antenna - still hisses. I plugged the AC into a different receptacle, and into a power strip - still hisses. Perhaps it needs a good cleaning? How is that done?

- theSpinnerBoy

[Boofers]

Have you tried selecting different inputs as well? How old is the unit?

[thespinnerboy]

The Rx-385 is from the mid-late 90's. Our local recycling center had an electronics recycling day a few years back, and I found this receiver there with a dent on the left rear top. Brought it home, found it didn't work, but I opened the unit and found the problem was a loose power cable that I was able to fix. Not sure if the dent was why it was discarded or if it received the dent at the recycling center before I picked it up. It was missing the remote but I found a universal remote that works with it. I've had it for years now and had no problems.
The unit started hissing badly last week. It hisses no matter which input is selected, and the hissing does not increase when the volume is turned up. I've unplugged all the inputs, tried it w headphones, tried a different AC receptacle. I think it needs cleaning inside. I have Radio Shack Tuner Cleaner and I thought I'd start with that.

[thespinnerboy]

The hissing seems to lessen as the unit warms up - is this a clue?

[thespinnerboy]

Hiss can be reduced, and sometimes eliminated, by going through the amp and replacing all the aging capacitors AND resistors (surprisingly, aging resistors contribute most to that low-level background hiss, in my experience). Using isolation transformers will further help eliminate some of it, or at least seem to eliminate background noise when playing music. I would guess that adequately shielded cables would also play a role. Even vibration damping, and shielding off sections within the amplifier (or perhaps putting the whole amp inside a Faraday cage?) might help.

But I don't think you completely eliminate it; you just reduce it below the audible threshold, at normal listening volumes. Turn the volume up high enough, and you'll usually still hear a little
hiss.

It's a lot of work to try to get rid of it, but I think it is worth some effort, at least up to a point. Recapping and upgrading resistors will usually bring the most significant improvement in this area, it seems.

[mrfeedback]

A mid nineties Yamaha will be full of suspect/bad solder joints by now.
Dismantle and inspect all boards and resolder as required - especially output stages and regulator stages.
Better is to blanket resolder output stages and clean boards.
My guess is that a low value solid cap is dry jointed, or a low value electro.
Resistors do not usually deteriorate.

Eric.

[thespinnerboy]

It seems two-channel stereos are the electronic backwater in a world of 6 and 8 speaker home theatres. A two-channel stereo receiver can be bought new for about one third of what they cost in the nineties. That being said, what do you mean by "electro"? Thanks.

[mrfeedback]

electrolytic capacitor....elcap.....electro.

[thespinnerboy]

The hissing is definately worse when unit is cold. As it warms up the hissing lessens. Could this be bc the solder is expanding and making a better connection? or could it the caps and electros do a better job when they're warm? I didn't think "solid state" had much of a warm-up issue.