Can anyone help me with a troublesome home theater problem?

December 19, 2005 7:41 AM

I'm having some problems with my AV receiver and I'm hoping someone here can help. I'll post the details inside.

In August I purchased a Yamaha Home Theater in a Box system. Specifically, I bought the YHT-760 system. It worked great for three months and then all of a sudden I'd get a lot of noise from my subwoofer. The way I decribe the noise is: imagine you're on stage and you have a microphone connected out to an am. Then you rub paper all of the microphone. I am getting a sound out of my subwoofer very similar to the sound the paper makes on the microphone as amplified by the sound system. Make sense?

So that's the sound in the sub. It's not always constant. sometimes it happens after a few hours of TV, but lately it happens whenever I have the sub plugged in. On top of that, the receiver has taken to turning itself off. I am told this is a circuit protection feature.

I have already brought the receiver in for repair and was told they fixed the problem by replacing a PCB. They tested it and returned it to me. Two days later, I got the sound from the subwoofer and then yesterday it started turning itself off again.

Yesterday I bought banana plugs to attach to the speaker wire into the sub. With those plagged in, I got the same sound. And, I bought one of these things to see if it was a problem with my outlet. The receiver still turns itself off (I have taken to keeping the sub unplugged.)

Can anyone give me an idea of what to do next? I am losing my mind with this problem!

Corollary: I seem to have a lot of static electricity in and around my living room. Can this have anything to do with the problem I am having?

I apologize for the length of this question. I just wanted to be thorough.

posted by bDiddy to technology (15 comments total)

Where do you have this thing set up? Is it in an enclosed cabinet? Is it on for long periods? These amps put out a LOT of heat, and heat is the enemy of electronics. Make sure there's ventilations aplenty. I imagine the circuit protect is triggered by temperature.
posted by cosmicbandito at 7:49 AM on December 19, 2005

Gotta agree with cosmicbandito about the heat - it makes electronics do all sorts of funny things. Adequate ventilation is a must.

On the sub, I'm trying to visualize (auralize?) the crackling sounds it's making. It sounds, to me at least, like a connection problem - I have this issue with bad cables between my syntheziser and amps.

I'd change the cable first, not just the connector. It's cheap to do that, and easy. If the problem still persists, then you need to localize the problem:

Can you hook up the sub to another system (a friend's, perhaps?) and test it out to see if it still does it on another amp? If it still does, and the problem follows the sub, you know you have a problem there. If it doesn't, then you might have a problem either with an amp setting, the sub circuit, or a bad cable, too.
posted by TeamBilly at 8:13 AM on December 19, 2005

I'll try running it in a more open area. It has a few inches of room on the top, but not much room at all on the sides, and the back and front are open.

I could put a few holes in the sides of the cabinet, maybe?
posted by bDiddy at 8:15 AM on December 19, 2005

It might be aesthetically odd, but see if you can rig a fan blowing on it for a while.

Also - troubleshoot one thing at a time. Don't change more than one variable. You're in good shape if you can reproduce the conditions and problem every time.
posted by TeamBilly at 8:40 AM on December 19, 2005

I'll try the fan. It won't be ugly if it's behind the cabinet, right? I've had the receiver hooked up to nothing and on another circuit and sitting on a hardwood floor with nothing around it, and it powered itself off. This was before I brought it in for reapir, but still.
posted by bDiddy at 8:44 AM on December 19, 2005

Hook the sub output of your receiver up to a regular hi-fi speaker* to test whether it's the receiver or the sub that's making the noise).

(* I'm assuming from your comments that the sub amplifier is in the receiver)
posted by cillit bang at 9:08 AM on December 19, 2005

Check that you have a constant, stable voltage coming out of your wall socket. I had a receiver and television that would sometimes turn themselves off. Turns out there were more than 120 volts coming out of my 110 socket, and I'm sure it was spiking from time to time as well. (The house I lived in was very old). I solved the problem by installing a power conditioner in my rack which insures constant, clean electricity. The particular model I have is the Furman PL-Pro. I got mine much cheaper than what's listed on the website at Guitar Center. Once installed, the LED's were constantly pegged in the red, but I got a solid 110 volts out of it, and no more problems with equipment shutting down. I know it's not a cheap solution, so you may want to try the ventilation options first, but to me it sounds like a power problem.

Also, make sure your system is properly grounded. If you've lifted the ground on any of your equipment, start using that third prong.
posted by Roger Dodger at 9:34 AM on December 19, 2005

Is it possible that there's a short in one of the speakers/speaker wires?
posted by I Love Tacos at 10:05 AM on December 19, 2005

Well, I got the Monster Power thing which says it conditions the power. I'm not sure if it's as good as the one you have, but it says it evens out the voltage. Anyway, it still happened this morning.

However, I don't think the circuit is properly grounded and I don't know what I can do to ensure that it is. I bought an outlet tester (plug it into the outlet and it has three lights that tell you what's going on) and it reported as hot/neutral reverse. I'm sure that's bad, but how bad? Anyway, the monster power thing tells me the line is protected (not grounded) and everything else seems to work fine.

I don't know that i want to rewire the outlet, but I will if it will fix the problem. I'd rather my landlord take care of it, but trying to coordinate our schedules so he could come in and take a look has been troublesome. Could I buy a better outlet at Home Depot or something?
posted by bDiddy at 10:08 AM on December 19, 2005

I suppose it's possible that there's a short, but I don't know. I ran it without any speakers attached and it still happened. I guess the short could be in the sub and maybe that's where the noise is coming from?
posted by bDiddy at 10:16 AM on December 19, 2005

Hot/neutral reverse is definitely a wiring problem. Fixing it is actually quite easy. Turn off the circuit breaker, insure that there is no electricity running through the outlet. Rewire the outlet, switching the white and black wires. White should go to the silvery screws, black should go to the brassy screws. White is on the side of the larger blade, black is on the side of the shorter blade if the outlet has two different size holes. Turn the power back on and check that the wiring is correct with your circuit tester before plugging anything back in. If there are extra wires or something you don't quite understand, refer here. Hopefully that is the only problem there is, but it is possible something else could be wrong as well.
posted by Roger Dodger at 10:38 AM on December 19, 2005

There are a couple things to check, but if your receiver has started tripping the protection circuit on a regular basis, it sounds like one of the amp channels is fried again. Based on what you describe with the sub, it sounds like you are getting some kind of short in the sub.

Is it possible to pull the subwoofer out of the box? If so, pull it out and check the wires. Look to see if there are any stripped connections or if the wires could move in some way that the positive and negative leads can touch. If everything is fine there, see if you can hear if the voicecoil is burned out. Make sure the room is as quiet as possible, then put your ear close to the cone of the sub. Gently push the cone in and let it out a few times, slowly. You are listening for a scratchy sound. If you hear that, chances are the sub voicecoil is fried, and that will cause the "rubbing paper" sound you hear coming through it, as well as a short that can damage your amp.
posted by ryoshu at 11:03 AM on December 19, 2005

The turning itself off thing sounds like a problem a friend of mine had with his Yamaha not long ago. Turned out there was a tiny short in the speaker wires and when a certain volume was reached, *click* off it went. We undid all the speaker cable and very carefully put it all back together, removing the short, and it hasn't happened since.

I'd guess whatever is the problem with the sub involves a short of some kind and that's causing your shutoff issues. I'd replace the receiver-sub cabling before I did anything else. Use any cheap crap you can grab - all you're trying to do is isolate a problem at this point.
posted by phearlez at 1:18 PM on December 19, 2005

Okay. Thanks everyone. I'll try a bunch of these suggestions tonight and let you know what happens. Hopefully I won't have to bring it to the authorized dealer to sit there for two weeks again.
posted by bDiddy at 2:52 PM on December 19, 2005

Tried running without the speakers attached, and it still powers itself off. So, I don't think there's a short in the wires or in a speaker. Unless, that is, the short caused something to blow out in the receiver already it just can't stay on. I will probably bring the receiver back in for repair at this point. I may not be able to do that for a while though, so maybe I'll try repairing the outlet first and see if that has anything to do with it.

Thanks for your help guys.
posted by bDiddy at 3:39 AM on December 20, 2005