Electrical Surge...from the speaker wires


New member
Username: Wayfinder

Post Number: 1
Registered: Jul-15
I have an Onkyo TX-NR3007 AVR and was installing an in-wall volume switch in a double gang box shared by a 110 outlet. I know better, but did not turn-off that circuit (hense the stupid tax I have paid). After wiring-in the volume switch (outside the box), while inserting the switch into the shared box, the volume switch accidentally contacted the outlet terminal and arced current to the volume switch. This caused current to flow via the speaker wires to the AVR. Now the AVR when turned-on just blinks the standby light and no display info appears. I know that these units are designed with fuses to stop power surges from the power cord, but what about this situation where it came from the speaker wires?

I took off the cover of the AVR to see if any fuses were obviously spent. There are 5 clear glass fuses I can see that appear to be good. There are also 4 fuses (I think) that have a white covering where the others are glass so you cannot see the filament inside to know if they are still good. Any thoughts if this is salvageable?

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18066
Registered: May-04

The power amplifier in your receiver is termed a "direct coupled" design.

I think from here you can guess the rest.

Direct coupled amps - as opposed to transformer or autoformer coupled circuits - have nothing between the output devices and the load (the loudspeakers). Even in the early transistor days when there were relays and fuses placed between outputs and speakers, the amps were still considered a direct coupled circuit (since there were no transformers between output and load).

Relays were largely and consistently unreliable and fuses limited current (and generally nastied up the sound quality) so both were given up long ago. You now have a simple and direct path between output transistors and the speaker connections in virtually any direct coupled receiver.

You can certainly check the fuses. Allow the receiver to sit for a day to dissipate any residual Voltage and use a fuse puller to remove the fuses. A DVOM ( or any simple continuity checker will confirm the status of the fuse. You cannot do this check with the fuses in their holder though or you'll simply be reading the holder's continuity.You must check fuses out of circuit.

It would be a rarity for any of these fuses to be inline between the output transistors and the speaker connectors. Doesn't mean it can't happen but I can't see an AVR having internal fuses that could so easily blow when a loud, sustained low frequency signal passed through. The receiver would be in the shop constantly for blown fuses.

Additionally, the constantly varying load a modern day loudspeaker presents to an amplifier would make it extremely difficult for any designer to select an appropriate fuse value for such a location.

Most likely, you've shorted out/opened up the output transistors by sending a 110 Volt surge at a full 15 Amps through them. The outputs blowing to pieces internally would be the only thing that stopped your service panel circuit breakers from flipping.

The blinking light simply indicates a problem which will not allow the system to power up.

I wouldn't hold out much hope for the receiver. Replacing the outputs - and hoping nothing else was damaged before they blew out - would likely cost about as much as a new AVR. A good chunk of any modern AVR would need to be disassembled to do the work.

At $60-75 @ hour for labor, costs really add up fast when AVR's must be disassembled. Then you'd need to be concerned about any up stream components that might have received a good whalloping surge before the outputs put a stop to the current flow. Even if you repair this unit, it might be trouble prone for the rest of its life.

Take it to a local service center, explain the situation and ask for an estimate of repair costs. That should run you about $40-60 which would be applied to any repair work performed.

The shop will inform you of the likely success of any repair work they might perform for your OK before they do the actual work or order parts. If you choose not to proceed with repairs, the shop keeps the trouble shooting fee.

Maybe, in such a case, the tech might open the receiver, take a quick look and a few measurements and simply say it's not repairable and they won't charge you anything. That's their call though so don't tell them I said they should do this for free.


New member
Username: Wayfinder

Post Number: 2
Registered: Jul-15
Thank you Jan, very informative. I spoke with the closest certified Onkyo repair center and they said the unit went into "protect mode" and estimated $200 (best case) to $400 (worst case) to repair. I thought that was fair, but have the same concern you mentioned regarding other damage that may have have been sustained that may not be immediately apparent. Plus this thing is 55 lbs and shipping it there (350 miles away) and back is another expense to factor-in.

Gold Member
Username: Magfan


Post Number: 3247
Registered: Oct-07
The receiver sustained something akin to a lightning strike, but from the speaker end NOT the power plug.

BTW, with the speaker wire in the same conduit as a 110 service you Would have, if you'll pardon the expression, gotten it from both ends. Any lightning strike or big power surge would have zapped the receiver power supply AND coupled back thru the speaker wire.

Otherwise? Heed Jan's repair advice.

And get the speaker stuff AWAY from the house current.

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 18076
Registered: May-04

Some (most) state and local building codes prohibit the wiring of low and high Voltage cable runs in the same conduit or box.

I'm guessing you did the audio wiring yourself.

If so, this could present some possible dangers as current flowing through the speaker cabling might not trip a circuit breaker or blow out the amp in a quick enough time to prevent a fire. It's a PITA to do so after the drywall is installed but do move the two cable runs away from each other. A sufficiently large lightning strike can cause issues with your audio cabling when it sits too close to high Voltage cables since they have a good chance of sharing a common ground point. Plus, your system will sound better (and usually also look better) when proper routing techniques are observed.

You can also ward off some bad joo-joo by using autoformer type vc's. They are more expensive but will give your AVR a bit of a more relieved load when all your home speakers are playing.

If you did the audio wiring, I'd certainly check local building codes to determine what is the correct lay out of your cables. You don't want to try selling the house and have an inspector raise a stink about your speaker cables. Since media rooms and whole house audio/video have become popular, this is an area many home inspectors check nowdays.

If you had the house pre-wired and you were only installing the vc, then you might have some liability to place on the installer.

Too many times home builders use the cheapest possible route to getting things done when they won't easily be seen or noticed by the home owner. I've been in situations where I'm installing the audio/video system and cabling and I'm working side by side with the alarm company's installer who doesn't even grasp the concept of stereo and mono cabling.

Drywaller's come in after the wiring is completed and, if the cabling sits in the wrong spot, a staple goes through the cable creating a dead short. All of these are the liability of the installer and the builder.

You may have some recourse if this was a pre-wired house. It also would be difficult to prove liability since you performed a portion of the work yourself. And, of course, is it worth your time and money to pursue such a claim?

Good luck. Sounds as if a new AVR is in your future.

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