Blown or Fried?

[Shahin]

Friends,

I own a JBL JRX-118SP (Spec sheet: http://www.jblpro.com/ProductAttachments/JRX118SP_specsheet.pdf). This sub has lasted me a long time, never causing any problems. At this point, however, it's not lasting at all. With an input verified by a LED signal light (see circuit diagram in spec sheet), I can confidently say it is receiving power and signal. However, I don't hear as much as a hiss coming out of the driver. It's completely silent.

How can I find out what's wrong with it? I don't think the subwoofer is blown, but I don't think it's a fault in the plate amp either. A blown subwoofer should still produce some sound, correct? I'm also not sure of the tools I'll need. Do I simply connect an ohm-meter to the positive and negative terminals of the sub to see if it's blown?

Thanks for the help. This sub is supposed to be running on Friday night for a big party we're throwing.

 

[j_garcia]

Likely IS a problem with the plate amp. Receiving signal does not mean it is able to send amplified signal to the driver.

 

[Shahin]

Thanks for your input J_garcia. If it were blown, it would most likely still be producing some sort of sound then, correct? And moving forward, is it possible to fix an individual component on the plate amp? Or is ordering a new plate amp the way to go?

 

[highfigh]

Thanks for your input J_garcia. If it were blown, it would most likely still be producing some sort of sound then, correct? And moving forward, is it possible to fix an individual component on the plate amp? Or is ordering a new plate amp the way to go?

What it does depends on what happened to it. If it was played at full output for many hours with music that it heavily compressed, lots of low frequency signal and below the port tuning frequency (if it has a port), it's possible that the evoice coil overheated and the wire broke. If it received one huge pulse, the wire to the terminals can break. If the sub amp pass DC to the woofer for a long enough time, the voice coil could be frozen.

Have you tried to move the cone? That's the first thing I would do. If you have a multi-meter, check the resistance of the voice coil and If not, connect a 9V battery to both terminals and watch/listen for the cone to move. If it doesn't, look at the terminals and look for evidence of overheating.

 

[j_garcia]

I use a AA battery, works fine. If you hear a click it is probably OK. If you hear nothing or a "scratchy" sound, it is damaged.

For the amp, when my plate amp died I had power and signal and no output. Often a fried capacitor in the output stage.

 

[TLS Guy]

Thanks for your input J_garcia. If it were blown, it would most likely still be producing some sort of sound then, correct? And moving forward, is it possible to fix an individual component on the plate amp? Or is ordering a new plate amp the way to go?

No it would not. Generally a blown amp is dead silent.

The only thing serviceable is the connection to the sub.

Remove the driver an make sure one of the two leads has not come off. If the driver is connected to the plate amp this unit is not serviceable and needs to go to the recycling center.

I doubt the plate amp for that sub is available. I have had a look at the unit. The plate amp does have some specialized inbuilt functions such as Eq and also limiters to prevent driver damage. So you can not use a generic amp.

I would comment that this unit would not now qualify as a sub if it ever did, as the 3 db point is 55 Hz. A lot of bookshelf speakers can easily make that, although they would not have the power handling or the sensitivity.

The problem is that the unit is dated and not worth money and resources. You will be better off putting funds to a newer updated unit.