dieing amps

[Hons Gruber]

Hey guys

So I have two amplifiers that are on their way out. I have some knowledge about amps, but know much more about speakers. I would like to learn about amps though. I am a teenager so bear with me here.

(I have a soldering iron)

Anyways I have a Sony SDR-D915. Its a receiver from the 1990 I think. My dad bought it was the hippest amp in the day or so he says. The channels are distorting. All the channels have a distortion and the phone channel is so distorted you can't even here the audio. I thought my mission's were blown at first.

My dad got a Denon receiver AVR-2805 a few years ago. It has been taken care of and hasn't really left its hole under the tv. over half the audio channels are dead some are very distorted and it is very very quiet. it has to be cranked almost all the way to be at medium volume I know that's bad for the amp for it to be cranked.

Is there any tests I can do to determine what needs to be replaced?
Thanks guys
peace,
matt

[mikje]

Are the controls either rotary or sliding potentiometers? If so, I would do a good de-oxit and faderlube job on them.
Mike

[Hons Gruber]

they are both rotary

[Hons Gruber]

I found one channel that works on my sony. Thanks for the offer of cleaning it, but I was actually looking to do the stuff myself if possible.

[mikje]

Oops, I guess that came out differently than I meant. I meant YOU could clean it. If you can get some electrical contact cleaner and clean all the controls, you might find that your problem has been solved.
Mike

[Hons Gruber]

ok I will try that. That could very well be the problem for the sony. You have any ideas about the denon?

[mikje]

Originally Posted by Hons Gruber

ok I will try that. That could very well be the problem for the sony. You have any ideas about the denon?

If you can get to the controls in the same way, clean them too. Oxidizing is a pretty common malady for equipment that has sat for any amount of time.

If you do a search for "de-oxit" on this forum and Audiokarma, you'll probably find some good "how-to" info from some very knowledgeable folks.

I don't know if have used contact cleaner before, but I'll give you a run down of how I do it.
Before anything else, unplug your equipment...
You have to be able to get the cleaner into the dirty pot or switch. That usually requires removing the face plate so you can see where the openings in the casings of the pot/switch are.
Then you need to be pretty liberal with the cleaner and really work the pot/switch its full travel at least 50 times. I usually put a rag around the pot I'll be cleaning to keep the cleaner form other areas of the amp.
After I've sprayed and worked the pot, I use a canned air to blow out the pot.
Once the cleaner has dried, which may take several minutes, I try it out. If it's still dirty, I repeat the process.
One thing I've found is that if a switch or pot still has cleaner in it that hasn't dried, it may sound like it's not working, at least until it dries.
Hopefully that'll help. If you have anymore questions, fire away.
Mike

[wakibaki]

Unfortunately Hons, I don't know either of these units.

The fact that they work at all is encouraging, but debugging a modern amp with multiple problems is not straightforward. Obviously there are tests which can be applied, but even to apply generic tests requires quite a lot of expertise and it's hard to get a leg-up onto the first level to know what you're doing.

The first thing you can do is photograph the boards inside the units in good detail, both sides, and post the photos. The photos should be well-lit all over, no shake, and you should be able to read the markings.

Look at the boards for things you can fix. Are there any leakages? Any burn marks? Any blown fuses (unlikely). Any obvious dry solder joints? Any fractures? Any serious corrosion, particularly on the connectors? Are there any marked voltages whose accuracy you can check?

This is about the limit of what you can do without a bit more knowledge.

At the next level you will require to be able to identify all or most of the components, the power supply, and be able to trace the signal paths. With a working PSU you can inject a signal and discover where it goes out of spec. Maybe. When you have power on it's easy to blow things up while testing, and doing it by remote control can be a bit tedious.

w

[Hons Gruber]

What kind of cleaner should be used? I'm going to guess not acid.

[mikje]

Electrical contact cleaner. You should eventually follow that with an "electrical contact lube" to prevent the surfaces from oxidizing again.
You can order some from Parts Express: De-Oxit and Faderlube. If you have a Radio Shack near your home you can check there too. I bought my current can at Lowes, so check there if you have one near you.
Hope this helps.
Mike