JBL VP wedge failure mode

B

Brian Bolly

Junior
Jan 11, 2011
429
28
28
Baltimore, MD
Had an interesting failure of two JBL VP7212MDP wedges last night. The boxes don't belong to me and I've got no dog in this hunt other than helping out a friend, but maybe someone with more VP series (or DPC amp) experience may have a better suggestion.

Mid-show, one wedge dies. Power & signal lights are still lit as normal on the amp module, but nothing is coming out of the drivers. I walk out to the truck to get a spare, and in the 2 minutes it takes me to get out there and back, the wedge has come back to life. However, not wanting to risk a failure again, I swapped it out with another wedge.

A few minutes later the second wedge dies in the exact same manner - power light is still on, signal light still flashing. Neither wedge was overheated - both amp modules were still cool to the touch.

As far as power, the wedges were in the middle of 3 boxes looped together via Powercon. Boxes on either side are fine, so I don't think it's a power issue. Here's the interesting part: in unplugging power while signal is still plugged in, right before the caps in the amp fully discharge and the wedge turns off, audio comes out of the box for a split second. This was completely repeatable on both boxes, but I've never seen this behavior before.

To recap:
- Wedge "dies" - no audio from drivers
- Power lights still lit
- Signal light still flashes
- Gain pot still attenuates based on LED intensity
- Amp not overheated
- Looped power - boxes on either side are ok
- Unplugging power results in audio for a split second before the wedge turns off, as the caps discharge

Thoughts/suggestions?
 
Re: JBL VP wedge failure mode

Brian Bolly said:
Mid-show, one wedge dies. Power & signal lights are still lit as normal on the amp module, but nothing is coming out of the drivers. I walk out to the truck to get a spare, and in the 2 minutes it takes me to get out there and back, the wedge has come back to life. However, not wanting to risk a failure again, I swapped it out with another wedge.

A few minutes later the second wedge dies in the exact same manner - power light is still on, signal light still flashing. Neither wedge was overheated - both amp modules were still cool to the touch.
Click to expand...
Brian,

You did not state whether the wedges were getting the same or different inputs. Assuming different inputs, perhaps the input used on the center wedge & replacement contained sub-sonic or UHF frequencies that trigger a speaker disconnect, when power is unplugged the circuit is deactivated, and audio then is passed until cap discharges.

Going top be hard to duplicate unless the console (or outboard gear) itself is passing sub-sonic or UHF frequencies, in which case any of the wedges plugged into the defective output will react in a similar fashion.

If the cause was upstream of the console, could be a bad cable (though unlikely) DI, instrument or wireless.

"Signal Processing: DSP based, resident in Input Module. System Management: DSP based limiters for mechanical and thermal
protection".

Any indicators on the wedge that indicate activation of the limiters for mechanical and thermal protection ?

Art
 
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Re: JBL VP wedge failure mode

Art Welter said:
Brian,

You did not state whether the wedges were getting the same or different inputs. Assuming different inputs, perhaps the input used on the center wedge & replacement contained sub-sonic or UHF frequencies that trigger a speaker disconnect, when power is unplugged the circuit is deactivated, and audio then is passed until cap discharges.

Going top be hard to duplicate unless the console (or outboard gear) itself is passing sub-sonic or UHF frequencies, in which case any of the wedges plugged into the defective output will react in a similar fashion.

If the cause was upstream of the console, could be a bad cable (though unlikely) DI, instrument or wireless.

"Signal Processing: DSP based, resident in Input Module. System Management: DSP based limiters for mechanical and thermal
protection".

Any indicators on the wedge that indicate activation of the limiters for mechanical and thermal protection ?

Art
Click to expand...

Art,

All 3 speakers were getting different inputs. All the wedge mixes were HPF'd at ~70 Hz, console was the band's Soundcraft Expression 1. We can likely rule out subsonic, but I don't know about anything up in the UHF band. But the 3rd wedge I ended up putting on that mix, although a different mfg/model, did fine for the rest of the night.

The only thing in this particular wedge mix were two vocal mics (SM58 and Beta 87) and an acoustic guitar on a Grace Design 'Felix' pre. I can't imagine any of those are doing anything weird subsonically or ultrasonically, but I suppose it's possible with the Grace.

There are 3 LEDs on the back of the wedge - blue (power), green (signal) and red (peak). Blue was on solid, green was flickering per signal level, and I never saw the red - the amp modules were relatively cool to the touch, and ambient temperatures were probably in the 60s as we were outdoors but under a tent.

I'm feeding all of this info back to the owner of the wedges to see if we can get any answers. I haven't heard anything back yet today, but we'll see what tomorrow holds.
 
Re: JBL VP wedge failure mode

I don't know how similar the voltage protection is in the VP series, but in the PRX600 series, if the voltage sags or exceeds by what seems about 10% of what the amp's looking for, the amp goes into "protect" mode. The power and signal lights stay on as you described, but no sound comes out. Took me a bit to figure it out(seems to happen the most on generator gigs), but I've had it happen to one box in the chain and another one won't be affected. Just seems to be a matter of how sensitive that particular box wants to be.



Evan
 
Re: JBL VP wedge failure mode

Evan Kirkendall said:
I don't know how similar the voltage protection is in the VP series, but in the PRX600 series, if the voltage sags or exceeds by what seems about 10% of what the amp's looking for, the amp goes into "protect" mode. The power and signal lights stay on as you described, but no sound comes out. Took me a bit to figure it out(seems to happen the most on generator gigs), but I've had it happen to one box in the chain and another one won't be affected. Just seems to be a matter of how sensitive that particular box wants to be.
Click to expand...

Thanks, Evan. This just might be the solution, as I believe the band power was a handful of 100' extension cords across a couple circuits. It was only a briefcase gig for me so everything was already set up when I got there, but I think we may have a winner. Now time to find a variac and do a proof of concept.
 
Re: JBL VP wedge failure mode

We have boththe vp7315 and the 7212. We had a pair of them behave similarly to as you described after getting hit with 144 v from a generator that the city electrician decided to turn up after we metered it. Had to send them off to jbl to get them fixed. The other two that were completely dead just flashed the fault lights.

Sent from my HTC6525LVW
 
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