Audio problem 900W active speaker

[jbelectric777]

Hi everyone, I have a Technical Pro / PROX12 900W speaker that when plugged in with no input goes directly to amplified distortion. I was thinking the problem was between the input and amplifier such as the crossover or maybe the amplifier itself....... I opened it to see what components they are using and there are about 5 boards in there. Before taking out and replacing boards I want advice from an audio expert, Im a master electrician and inspector (electrical) my electronics is not strong, maybe slightly above novice. I'll repay with any thing I could help in my area of code and wiring. Thanks so much! Jim

 

[CocaCola]

Look for obvious damage, swollen parts, leaking/oozing parts, parts with black or white power residue on them, discolored parts, parts with visible damage like a crack or hole, visibly burnt parts, parts that are giving off a rank smell...

Look closely at capacitors...

 

[jbelectric777]

Thank You , I think I do see the white, I took the boards out, the crossover and the amplifier, the crossover looks fine. I noticed the board says P1712-180W-AMP....... Is this telling me its a 360 watt amplifier? going to 8ohm speakers 1 woofer 12" 1 horn, this was sold as a 900 watt loudspeaker....... also is there any way to find out what company makes this board? TP doesnt make em, they order em and install em in the plant. Thanks for any and all help, Im thinking of just putting an amplifier with crossover inside the shell and driving the speakers that way, customize the input and the volume, treble, bass knobs. I only use it for the DJ part of our buisness, a guitarist plugged into the microphone input and about needed a change of underware ! yea its ok at low frequencies and low volume but this guy was crankin it! well, we go and set up for a bar opening and poof.. it went, thank goodness I had an 800 in the truck! but now i feel like it could happen again so I'd rather run 3 medium than 2 high....... What do ya think. Jim

 

[jbelectric777]

i see a lot of white powder mixed in with some type of lubricant or anti corrosion seal on the 4 power transistors that rest with the back right on the heat sink, i could send a photo if it would help....... Jim

 

[CocaCola]

One could write a book on how audio amplifier companies twist and for all intents and purposes lie about ratings... Especially if they are not high end name brand companies that care about their reputation...

There is much more involved and it's far more complex then this... Lets say your amp is rated for 600 Watts... Now in the real world it's 100 Watts @ 8 Ohms, 200 Watts @ 4 Ohms (assuming the amp is stable at that ohm rating) now drop it down 2 Ohms and all the sudden it's a 400 Watt amp... Put said amp in a freezer, give it say 20% over the 'average' input voltage (aka if it's a 110V amp, supply it with 135V or so) and blow a stream of freon over it for additional cooling... Now you might be able to get it to pump out 500 or even 600 Watts @ 2 Ohms before it smokes... And like magic Presto you have a 600 Watt amp, you can label it a 600W amps since you were able to get it to do that before it smoked... No lies and no false advertising even if unrealistic...

Or you simply don't care and you label it whatever you want, like a vast majority of the cheap amps coming out of Asia...

As from where you go now, there are lots of options, repair, replace or as you suggest hack into something new...

*** edit photos always help

 

[jbelectric777]

kinda like having a 14 gauge copper conductor cold enough to carry 50 amps without any heat....... i see what ya mean. Well I pulled the board out and the white powder looks like it came from one of the 4 final stage output mosfets, they are Toshiba 2SA1943 and 2SC5200 and it does look like one or more may have exploded, literally because its all over both boards, Im gonna see if Wallco electronics has em, order if needed and replace em, it makes sense now if they are shot, the power will go 100% high bypassing everything, I dont even have the 5 or 6 second relay delay so Im hoping its those MOSFETS, hey 12 little solder connections and I may save a 250 dollar speaker. I know they arent the best but my dads my partner and doesnt understand the DJ /audio business, we have a nice lighting show but thats more my area ya know, I think we both just expect these pretty black cabinets to work! NOTTTTT !! Thanks for all yer help, worst case scenario I buy a new one and make em pay half

 

[jbelectric777]

buy another one but not TECHNICAL PRO i do like GEMINI but i think its just the owner of TP's brother. they seem better tho.

 

[jbelectric777]

that powder/silicon is dry now and i got some in my eye, its not hazardous is it? i just flushed with cold water and it feels ok. the manufacturer specs on those mosfets warns about temperature change and the problems it can cause, we did a wedding no problems and knew in a few days we had the bar grand opening so we left them in the van, im in north east pa and it got cold those nights and i plugged em right in, in a few seconds is when the ear peircing buzz went off scaring everybody! i wonder if that had anything to do with it?

 

[jbelectric777]

im also installing 12vdc fans on top of every unit i own to keep the heat down, that may get me better operation as well, it should be law! to put em in....... thats why we have codes etc, they can do anything so long as the UL listing is on it i guess

 

[jbelectric777]

coke a cola, I was looking further and noticed a tan colored glue like substance around one of the 3300uf caps, at first I thought it was glue from the manufacturer but looking further it has no rhyme nor reason to be there, it may be some sort of dielectric fluid in the caps? maybe some insulating material? I think I'll replace those as well, the white colored gel that was between the back of the mosfet with a peice of plastic type material may be for transfer of heat to the heat sink. Those caps basically look like they are leaking this material. What do u think? Im gonna get back into electronics, most of my know how is logic and things that work hand in hand with motor control and plc's etc, my audio is very weak, now in the entertaining end of it, I wanna know what went wrong and have a small stock of component level parts, its easy to just buy one but eventually they just go, for no reason. Now I'll have the parts and know all stages with audio amplification anyway. I guess I could get an external amplifier and make these speakers all passive if I wanted to.

 

[CocaCola]

Post some pictures...

As for the UL listing that certification stamp is supposed to be on the final design... But, if you actually research it you will see that although the intentions of UL (and CE) are good it's mostly become a circus act and pretty face to slap on things... I has little to noting to do with actual quality or performance... Especially if the company is self certifying on their own honors system like many are... And if you are an Asia company that doesn't give a rat's poop, they will simply sticker it just to get past import regulations because they can and will usually get away without issue doing so...

 

[KrisBlueNZ]

I agree with CC, please post some clear photos including closeups of ALL the boards.
Is it possible that the white stuff is just thermal paste? It looks like toothpaste and is put between the power transistors/MOSFETs and the heatsink to improve heat transfer.
Photos are the next step. Without them, everyone is working in the dark. If there's anything suspicious on the underside, post photos of that too.
Be glad that CC is helping with this. He always has good advice.