What is causing this fault?

[Klemay83]

In my venue we have flown arrays. 6 arrays either side (RDF HDL20a active array units) over the past 3 years at least once a year one unit gets a blown amp module. I've attached some pictures from 2 units that I opened up and removed the blown amp modules from.

As you can see its the 2 Yellow capacitors that seem to rupture..

what I want to know is what is causing this to happen. is it a power issue or is it an overdriven signal?

the first 2 pictures are from the most recent amp failure. and the third one from a unit from last year where it actually started smoking...as you can see by the extensive damage. but both units have the failure at the same place.

any info is much appreciated to try and hep me get to the bottom of this.

[Leo_Gnardo]

what I want to know is what is causing this to happen. is it a power issue or is it an overdriven signal?

the first 2 pictures are from the most recent amp failure. and the third one from a unit from last year where it actually started smoking...as you can see by the extensive damage. but both units have the failure at the same place.

any info is much appreciated to try and hep me get to the bottom of this.

Do the failures happen while you're banging a huge signal thru your system, or at random? Even under no-signal conditions? Whichever is the case it's very uncomfortable to say the least, to have flying gear catch fire. I'd contact the manufacturer, ask them if they have a solution, and let them know they're on the hook for a good answer - or get rid of those speakers before they cause a disaster & replace them with a different make that doesn't have a reputation for spontaneous combustion.

[Klemay83]

Do the failures happen while you're banging a huge signal thru your system, or at random? Even under no-signal conditions? Whichever is the case it's very uncomfortable to say the least, to have flying gear catch fire. I'd contact the manufacturer, ask them if they have a solution, and let them know they're on the hook for a good answer - or get rid of those speakers before they cause a disaster & replace them with a different make that doesn't have a reputation for spontaneous combustion.

The amps go when they are in use. The unit will start to hum and the power light goes out, indicating the amp module has blown.

[J M Fahey]

I only see two burnt resistors on the third picture, which toasted everything around them, from capacitors to inductor, but first two show no damage signs.

[Klemay83]

I only see two burnt resistors on the third picture, which toasted everything around them, from capacitors to inductor, but first two show no damage signs.

But what causes the modules to stop working and produce this high pitch hum (sounds like a bee buzzing)?

[rjb]

Pulling this out of my ass:

SMPS filter caps are failing due to too-high ESR (power dissipated = ripple current squared x ESR).

- rb

[Enzo]

Could be anything. heat buildup, transients, funny mains, and on and on.

[nickb]

FWIW, what you are showing looks like the output filters of an H bridged (or maybe paralleled) class D power amplifier.

I can't see the problem with the caps from any of the pics, but, if they are failing, I would guess it's due a poorly specified or bad quality capacitor. Possibly the dissipation factor is too high leading to excessive internal heating. The manufacturer might have an ECO (engineering change order) in effect that mitigates the problem so try bringing it up with them first. Failing that you would have to substitute a 'better' capacitor, something that is very hard to do without all the facts.

[J M Fahey]

Quote Originally Posted by J M Fahey
I only see two burnt resistors on the third picture, which toasted everything around them, from capacitors to inductor, but first two show no damage signs.

But what causes the modules to stop working and produce this high pitch hum (sounds like a bee buzzing)?

No doubt you have a problem, but so far nothing tells me that those caps are guilty or have any problem at all.

Please ask makers for the schematic and post it here, itīs the minimum needed to even suggest some troubleshooting steps.

Note: you state "extensive damage" and *maybe* you are referring to the dark paste like material on the caps and some nearby components ... itīs just a silicone rubber material applied to large heavy parts to avoid vibration cracking their legs, nothing else.

Visual inspection means little, parts can look very good and actually be very dead, youīll need a schematic (even better a factory service manual) , proper equipment and knowledge on how to use it to try repairing these complex units.

Not to discourage you but even seasoned Techs often order a new stuffed and tested PCB from Factory and just replace it.

EDIT: you actually meant RCF HDL20A which are U$3000 cabinets (in USA) .

Do not even *think* about home repairing them, if within warranty, use it .

If not, ask local Authorized Service to order and replace new modules, period.

By the way, you do not show what Country are you writing from.

[paleeman]

Common problem with these. Due to extensive vibrations, components break off from the PCB. You should inspect every larger component visually. If you're lucky, you just need to solder the broken components back, and off you go. However, if you're not, component level repair is not advised.

BTW, the third picture, it is not of a HDL-20A module.

[glebert]

I'm surprised there are no heatsinks on the FETs. Maybe that would cause more of a vibration problem than it would solve any thermal issues, but these aren't exactly low power arrays.

[paleeman]

I'm surprised there are no heatsinks on the FETs. Maybe that would cause more of a vibration problem than it would solve any thermal issues, but these aren't exactly low power arrays.

The FETs are mounted on a large heat sink, which is the back plate of the unit. Klemay83 posted a picture where the PCB is removed from the heat sink.

(picture downloaded from Ampman Audio)