Did a toddler break my speakers?

June 22, 2012 5:24 AM

I have a pair of vintage Bose 501 speakers that have worked great for the past five years. They are connected to a vintage Yamaha CR-820 receiver. A while ago, my favorite toddler pushed all the buttons on the receiver and the speakers stopped working. She came over again, pushed a bunch of buttons and it started working again. Next time: bunch of pushes, stopped. Now no button pushing seems to matter... is it broken?

In between button-pushing sessions, the speakers make a random, horrible sound: like a repetitive, scratchy, high pitched squeal.

The only way I can get them to work and it's not always, is to send music to it, turn the volume up all the way, wait about a minute until I hear the faint sound of the music, turn it down just a little. At this point there will be weird vibrations and horrible sounding squeals until the music takes over. Then it's fine. I can stop playing the music for about 30 minutes, turn it back on and it works. But if I stop for an hour or more, the speakers won't play and I can't do the turn-the-volume-up trick. I have to power off the speakers so they don't randomly squeal in the middle of the night and wait several days -- it seems -- before it'll work again.

Anyone have any ideas as to what's going on?

posted by 10ch to technology (6 answers total)

My completely inexpert opinion is that something's wrong with your receiver. Have you got other speakers to test it with?
posted by Magnakai at 5:35 AM on June 22, 2012

Weird weird weird. Are the speakers powered independently, or through the receiver? I wonder if the squeal is a bad signal being sent from the receiver, or if it's being generated internally by the speaker, or perhaps by the cable. Does the squeal continue if the receiver is unplugged? What if the speaker audio cables are unplugged? Given the presence of a toddler, how are the speaker cables looking? Have they been yanked out or chewed on? (Put them out of reach!)

Somewhere there is a device which cuts off the output when there is no music to play. I suspect there might be a short which is overpowering this device and throwing random power supply noise at your speakers, which are dutifully amplifying it like they're supposed to. But when the receiver is on, it's in turn overpowering the short and you get music. Maybe it's a very weak short and there is a temperature-dependent component due to thermal expansion/contraction of the wires -- there could be a wire which is on the brink of failure when cold, but works once it's warmed up. I would not continue to use this system until it's fixed - if there is a short, then you could get further unpredictable failures and there could be risk of a shock or even a fire. I'm still not fully sure what's going on, though.
posted by PercussivePaul at 5:56 AM on June 22, 2012

Hmmmm. Well, it's most likely your receiver that's got the problem, not your speakers.

The high-pitched squealing (especially the "randomly in the middle of the night part") makes me first think that you have some electronic components in your receiver called capacitors that are going bad.

The weird volume thing makes me think it's possible there's some bad solder joints and/or some integrated circuits/transistors in the receiver that are starting to die.

This might be just coincidental timing not connected with the toddler button-pushing, or it's possible that some bit of conductive material or dirt got lodged someplace it shouldn't have and is making weird connections or is preventing important connections from being made.

Magnakai's idea is a good one - if you have another receiver & another set of speakers try swapping things around & see what happens.

It's possible your receiver just needs a good internal cleaning, which you can DIY if you feel so inclined. Otherwise, I'd say take your receiver in to a repair place, if you can find one.
posted by soundguy99 at 7:00 AM on June 22, 2012 [1 favorite]

Yeah, I agree with everyone above that you should narrow in on your receiver as the problem. Since your speakers are passive (as opposed to active speakers that have their own built in amp) they will mainly just work or not work and the issues you will hear with a speaker problem will be lack of sound in a particular section, for example a sudden loss of high tones or sometimes a low physical hum/rubbing sound or flapping sound.

I'd blame all squealing and especially scratchiness when buttons are pushed or knobs are twiddled on the receiver. Since the receiver is also vintage it is highly likely that at least one of your problems is dirty pots. Over time the lubricant on the knobs and switches breaks down and gathers dust and this can manifest as scratchiness in general and specifically scratchiness and hum that is affected when you twiddle the knobs around. The good news about that is that you can usually clean that right up yourself.

Here is a link to an internet forum about vintage audio. It's a thread that explains how to employ Deoxit, a product I've had great success with myself. I'd take a good cleaning as step one. Then after you've successfully completed that you can see if your problems persist.

I'm not going to make any predictions because I've seen some pretty bad problems fixed with a cleaning of the pots but it is not unheard of for old and failing solder joints to cause intermittent lack of sound that comes and go. If that's the case and you feel handy enough it's likely that you can get your hands on a service manual for that model of receiver. I also suggest the forum I mentioned above as a great source of help for people wishing to repair their vintage audio. Good luck!
posted by tinamonster at 8:29 AM on June 22, 2012

The first thing i do with mystery issues with any of my ancient hi-fi equipment is open it up and blow out everything witha can of air. Probably a 70% success rate. if that doesn't do it, I take it to A Guy.
posted by cmoj at 11:33 AM on June 22, 2012

Old receiver? Check the 'tape monitor' button.
posted by DandyRandy at 11:36 AM on June 22, 2012 [3 favorites]