My JBL MPX1200 is now a smoke Machine

Hi, I've had this amp conected to two 8 0hm bandpass subs each containing 2x 16 ohm pd156's. So the amp was running 4 ohm bridge. The amp is rated 3200watts into 4ohm bridge and the total watts for the speakers is 2600. It's been running fine for about two months in an install until last night when it starting pumping out acrid white smoke. Strange thing is there was no visible fire, the bass bins where still playing and sounding fine and the amp was'nt even warm. In fact the amp has hardly broken a sweat in the time it's been used as the venue is fairly small and it's certainly run nowhere near clipping. It mainly used for rock disco's with the occasional band. Any one come across this before and have any idea if the amps worth repairing or not?
cheers[img]smileys/smiley5.gif[/img]

If the amp was still working fine and not even warm, it could just be a mains input filter capacitor gone bang (or something else non-essential to the actual operation of the amp). We had this happen at work on an expensive HP signal generator.

would this be expensive to repair, and is the white smoke dangerous, it was pumping it out.

Probably quite a cheap repair. Taking the lid off should give you a pretty good clue as to where the problem lies and a photo of the incinerated component will give us an idea of how big a hole it's going to burn in your pocket.

As for the toxicity of the smoke... It's probably not too good for you, but there are probably less nasty chemicals in it than cigarette smoke, which 13 million Brits deliberately inhale every day...

If you switch it on again, you may well find it doesn't smoke any more, since whatever went pop has now gone pop and become open circuit.

thanks for your help i'll rty and get a photo fairly soon!

could also be the capacitor in zobel network

I have no idea what either of those thing are! but i'll try and get a photo up soon

Sounds very expensive to repair... Think it would be best for you to sell the amp as is to me...

Seriously though, I was told last week the PSU caps need to be replaced on older amps, as theyhave a tendency to detonate, and attempt to remove amp cover in the process.

Electrolytics do dry out over time, to a greater or lesser extent, depending on the quality of them, their temperature rating and the ambient temperature they've been working in.

I've serviced some Crowns which are over 25 years old and the smoothing caps were still fine. Conversely, I bought a LAB1000, which was about 15 years old and the caps had emptied themselves all over the inside of the chassis.

Any more news on this one? Photos or anything?

I've replaced tons of capacitors in computer mainboards. they dry out/get old, pressure builds, safety cap pops and it vents the electrolyte out - the capacitor does not have the capacitance it once had and starts to resist current.

If it's a capacitor that let out the magic electronics smoke, open the case up, find out the voltage and capacitance of the one that damaged, (& try to match the ESR or beat it if you can) and replace all capacitors of the same type in the amp.