Speaker Short circuit?

BobHol

BobHol

Old fart
Saturday I get my Onkyo Tx-890 receiver back from repairs.
It had been blowing an internal 7 amp fuse and I didn't feel skilled enough to fix it. So I get it home hook up all the inputs and connect speakers to A and B. Plug it in to power and as soon as I push the power button I get a flash of light from inside the receiver and a small puff of smoke. I dive under the desk and unplug the power. The next day I take it back to the shop.
The owner is determined to "make things right". Today I get a call from the repair shop. The owner says they fixed whatever was burnt but are clueless as to what caused the problem.
Their only guess is that one of my speakers has a short, or maybe I had speaker wires touching each other. I have no idea where the volume control was set at.

My question is what usually happens when speaker wires are accidentlly touched and shorted?
 
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BobHol said:
Saturday I get my Onkyo Tx-890 receiver back from repairs.
It had been blowing an internal 7 amp fuse and I didn't feel skilled enough to fix it. So I get it home hook up all the inputs and connect speakers to A and B. Plug it in to power and as soon as I push the power button I get a flash of light from inside the receiver and a small puff of smoke. I dive under the desk and unplug the power. The next day I take it back to the shop.
The owner is determined to "make things right". Today I get a call from the repair shop. The owner says they fixed whatever was burnt but are clueless as to what caused the problem.
Their only guess is that one of my speakers has a short, or maybe I had speaker wires touching each other. I have no idea where the volume control was set at.

My question is what usually happens when speaker wires are accidentlly touched and shorted?
Click to expand...
Output transistors usually short out-burn up in a fraction of a second followed by burning resistors until the fuse blows.If theres a speaker protect relay involved it usually ends up with overheated ,melted or welded contacts.
A shorted speaker or speaker wire will short out the power amp in a nanosecond and it doesn't matter where the volume control is set.I would definitely make darn sure your wires or speakers are in serviceable order before hooking them up to any amplifier.
 
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Who's to say for sure? It's definitely a possibility that a shorted load could have taken out the output section.

Just make sure that there is no issue with the wiring and/or the speakers before reconnecting the freshly repaired amp. I'd give the tech the benefit of the doubt here.
 
Depends on the amp and many other factors.

Some amps can handle being shorted out for quite a while with no problems
or blown parts.

Depends on the volume setting or the amount of power being disapated

and the type of protection circuitry involved.
 
A speakers ok but internal short for B ?

Thanks for the replys.
I will definetlly offer to pay for the repair. (I'd say bad Karma not to). This receiver is an Onkyo Integra(tx-890) and when new it was spec'd to go down to 2 ohm but that doesn't mean it could withstand a dead short, plus by the look of the unit it has had a rough life.
My only other far fetched thought is that the unit tests fine on the A speakers but there may be an internal problem with the B speakers ? As you can tell I've never worked as a "stereo tech".
 
markdi said:
Depends on the amp and many other factors.

Some amps can handle being shorted out for quite a while with no problems
Click to expand...
True..But those that can are usually on the very spendy side.Would you want to risk it?

Depends on the volume setting or the amount of power being disapated

and the type of protection circuitry involved.
Click to expand...
Depends on the volume setting
Click to expand...

Not on a direct coupled amp.Which 90% of the japanese are.Rail voltages are always present on the output transistors collectors leads reguardless the volume setting.I gaurantee if you short the speaker leads on a power amp without a pre-amp even hooked up your going to burn something.
Here is what happened to a Yamaha M-4's speaker protect relays that the speaker wires got shorted. The preamp wasn't even powered up yet.It took out a set of output transistors as well.
 

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I had a woofer that went bad and now tests as a dead short. Took one channel of my power amp with it. In the repair shop now.

Basically, I lost the 1 channel of my amp and so I hooked up a spare amp. That's when I noticed the woofer was bad. The good new is it didn't damage the second amp. Good karma in a way I guess!
 
If the volume control is turned down all the way there should be no ouput from the amp and therefore even if it is shorted, the amp should not fail. Most receivers and amps have a current limit circuit to protect the amp for shorted speaker cables. Any amp I work on that has this feautre gets tested by shorting the output at full power. If it doesn't survive than I fix it.

I think the repair shop missed something or there was some loose hadware floating around. It's not the owners' fault.
 
d3imlay said:
I think the repair shop missed something or there was some loose hadware floating around. It's not the owners' fault.
Click to expand...

I think that's jumping the gun.

I've seen a lot of customer load induced failures. Sometimes protection circuits aren't fast enough. Protection circuits take time to activate. Chances are better that an overcurrent protection scheme will work for 2 ohms, rather that 0 ohms. The current and the heating in the outputs will rise much faster while waiting for the protection circuit to activate. It takes time for the local heating on the die to get to the transistor package, then to the heatsink.

We used to do the dead short test with Soundcraftsmens all of the time. They had a crowbar that would short the filters and blow the fuse or open the TRIAC. Soundcraftsmen protection circuits were unusually good though. It would still scare the piss out of you every time you pressed the shorting button.
 
d3imlay said:
If the volume control is turned down all the way there should be no ouput from the amp and therefore even if it is shorted, the amp should not fail.
Click to expand...

What is the first inherent action of most people when turning up the volume and nothing seems to be happening? Yup...turn it up more. :yes:

A more likely situation, one which I saw first hand, was moving a speaker with the system cranked up pretty good. The guy moving the speaker stepped on the cable, it pulled out of the speaker terminals and shorted together, and that was that. Amp went to the repair shop on Monday for a blown channel...and it wasn't just fuses.

I don't disagree the protection circuits should work, but as Avionic eluded to, not all of them seem to be 100% foolproof/robust.
 
If you are re-testing a KNOWN speaker with a problem (which is what it sounds like you have), my best recommendation is to test the speaker PRIOR to hooking it up to something valuable.. One really good CHEEP test would be to grab an old CB radio with a PA.

Fashion a suitable cable (usually 1/8" mono on the radio end to whatever you need on the other.. hopefully a couple of bare wires for testing), connect it and power on the CB in PA mode. You don't even have to have an antenna attached for a PA test.

I've got an old 19 channel Radio Shack mobile I've had to 20+ years. The actual radio unit is 1" x 4" x 8" and runs on about a .7 amp fuse.

Any ol' CB will do the trick if you have around an 8 ohm speaker to test..
 
Or, you could just go to about any store that sells automotive or electrical stuff and buy a cheap multimeter. I think I paid ~$15 for one when I was in a real pinch one day. It works just fine for testing your basic voltage, resistance, and current measurements.
 
It could have been a bad speaker, but consider the speaker wiring.
Something I have seen frequently is multi stranded speaker wire have a single strand escape and short to the adjoining lead, it's good practice to "tin" your speaker leads to prevent that.:thmbsp:
Casey
 
Yamaha C-1020 speaker-wire short

Hello,
This is my first post in AK. It has been my great resources.

I know this is an old thread, but I got an exactly same trouble. I was playing Yamaha A-1020 yesterday, and thought there was some distortion of the sound. When I was checking the speaker wire connection, I accidentally made a shortage of speaker wires. It did not cause any crack, smoke, or flash, but I simply lost the sound. The speakers were intact (I checked with another amp). I open the A-1020, and did not see any burning signs or smell. I checked output transistors, and they worked fine. I opened the relay, but I did not see any burning marks. Which part(s) could be a problem?? Your help is much appreciated!!
 
If you're gonna play with electronics, you should own a volt-ohm-meter.

If you're gonna play with wood, you're gonna need a means of measuring it.

Same difference.
 
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