Checking LSI15's for short

Brasiliaflyer

I just got my amp repaired after frying several mosfets and a resistor. The repair shop told me the issue occurred because of a shorted speaker. I've looked at the cable, and there were no loose strands or anything, which leaves the speakers themselves. How could I check them using a multimeter? I've heard that the resistance can actually change while being checked due to the multimeter charging capacitors or something like that.
In a side note, the speakers sound good. Can a speaker with a shorted component still sound ok? Thanks!

nhhiep

do you know if your amp can do 4 ohms or less?

Dennis Gardner

If they sound good, I would doubt there is a short. I would more likely think that the 4 ohm nominal impedance of the 15's were simply too tough of a load for your amp.
Constant reheating of those innards in your amp caused the weakest link to let go.

Brasiliaflyer

Yes, it's a b&k amp. Easily does 4 ohms.

Dennis Gardner

Brasiliaflyer wrote: »

Yes, it's a b&k amp. Easily does 4 ohms.

Nice amp, you may have some type of crossover issue. You can always check for impedance differences on the speaker terminals. It is simple to compare Left readings to Right, for a start.

F1nut

You can check resistance at the binding posts, but you cannot check the nominal impedance there. If there was a short in your speaker(s) it would have damaged the amp again. I'd bet the amp was the real issue.

F1nut

I've looked at the cable, and there were no loose strands or anything

Are you using bare wire at both ends? If so, you could have easily had a loose strand at the amp end, which you wouldn't see now. Bare wire sucks, use bananas or spades.

Brasiliaflyer

Can a short cause the amp to give up not immediately, but after several hours of listening? I like the idea of comparing the two speaker's resistance, but the amp went out after idling (on but no input) for several hours. As soon as I hit play on the cd player, there was a puff of smoke. I'll talk to the tech who fixed it again to see what else could have caused the problem. Maybe the lsi15's have some sort of intermittent short.

tonyb

Didn't you buy that amp from someone used ? Not that it's bad, but chances are it may have had some tinkering done on the inside.
I highly doubt it's the speakers. Maybe you had some strands of speaker wire touching both posts on the back. B&K amps are pretty bullet proof. How about ventilation, did you have enough air around it ?

Brasiliaflyer

I did buy it used. The reason I think it's something other than the amp is because this is the second time it's happened. It's already been back to eeav for repair once, and they said they went through everything and said it was perfect. Got it back, used it for two weeks and it went out again. It souded phenomenal, by the way, for the two weeks I had it. Plenty of ventilation, only hooked up to two lsi15's (out of the seven channels). I'm baffled.

Drenis

Is it one channel that fries? Same channel?

Have you used the speakers before without incident? I mean it is possible something MAY have come loose...

Also, F1 is right, bare wires are terrible. All it takes is one loose strand that is NOT easy to spot especially in not so forgiving lighting conditions.

tonyb

Agreed ^^^, plus you have to check all bare wire connections, speaker side too and the cables themselves. You could have some plastic coating removed somewhere along the run and it might be brushing up against some metal, either from the rack or another piece of gear. What kind of cables and interconnects are you using ? I would be looking from the amp back, as soon as a signal was sent, it blew, so follow that path back. Maybe a bad connection with the output terminal in the receiver ?

Brasiliaflyer

Well, the amp is going back to EEAV. I dunno. I checked the speakers with a multimeter, and they measured around 4 ohms. No short in the cable or anything. Starting to wonder if there is something loose in the amp itself, or if the speakers have an intermittent short like in the voice coil or something that only shorts once in a great while.
I'm perplexed because when EEAV had it they burned it in, ran it at full power, etc... Said everything was strong on the amp.
I did check the terminals on the amp for a short with the multimeter, and I couldn't find one.

Dennis Gardner

I wouldn't worry about it. I might run it hard for awhile on a different speaker pair. They guarantee their work. If it fries itself, they will cover it. I would only worry about issues with parts down the road since they (B&K) are recently defunct.

F1nut

As soon as I hit play on the cd player, there was a puff of smoke.

Be sure to mention that info to the repair tech. I still don't think the issue has anything to do with the speakers.