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NEED HELP! Epik Legend plate amp repair thread


mustang guy

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It's really quite a bit of fun learning about that stuff. Be careful, there are lots of ways it can bite you. I never shocked myself and stopped my heartbeat, but I have jumped a few times!  When you put the caps in BE SURE TO GET THE POLARITY CORRECT!  They do tend to explode...   :)

 

edit: I assumed you were a beginner. Something tells me you are not... My memory aint all that good...

 

 

It doesn't bother me to be told to take heed to polarity orientation, you can never be TOO careful. Fortunately, the boards that are silkscreened have the schematic part #, value/voltage and polarity marked on them. 

 

I already ordered parts from Mouser, mostly Nichicon audio grade capacitors...I had some 1uf 50volt caps stashed away to get things started.

 

It seems to be a fairly simple project so far. The only custom fabrication I'll have to do is mount a snap-in cap in place of the main reservoir cap, a old big Elna 2200uF 63volt unit. I can mount the snap-in on a piece of perf-board, and then mount that to the chassis. Along with a re-configuration of the ground leads with respect to the negative terminal of the Elna 2200uF cap.

 

They have like way too many wires soldered to that poor little ground terminal of the Elna. I would imagine this is the way it was wired at the factory. It's a Taiwan made model, series B1.

 

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It takes a LOT of heat to solder like that! 

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I have a problem. I got it all connected and put power to it, and the fuse blew again. Not easily deterred, I tried another fuse, and watched closely to see if there was any visible reason for the short. The thermister sparked and blew out. Upon investigation, the web tells me it is definitely due to a dead short, and likely a short in a diode, as they almost always blow to short when they go bad. Remember the burnt place on the pcb? Well, I think that's the end culprit. What I am wondering is if the pictured are actually diodes, and if so, how do I know what diodes they are:

5OgrFEs.jpg

Here is the thermister (green in center):

hRoAmeb.jpg

Edited by mustang guy
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I can only be of help by giving your thread a free bump.  :sad:

+++

 

My common sense tells me that where the board is burnt that is where the heat was generated which probably caused the catastrophic failure.  What doesn't make sense to me is how things would have gotten so hot after the fuse blew.  That looks like that was a really hot spot for a while.

 

Also, you seemed to have clearly identified a Mosfet which you tested and found to be bad.  I know there can be a cascading effect of parts failure, but for the most part, I look for one problem when there is a failure.  I don't know diodes enough to know if you can test them or not.

 

Where are you researching the problem and solutions?  I think there is an AVS.com thread that addresses this, but I haven't read it for a while and I don't know if anyone was successful in accurately identifying and fixing the problem at the board level.

+++

 

Edit:  A guy on AVS.com claims he "fixed" his, but more accurately he identified the problem as two leads on the driver were touching, and had actually fused.

 

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/885079-official-epik-subwoofer-thread-504.html#post24211415

Edited by wvu80
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Has anyone put an external heat sink on the Epik Legend plate amp?  It has a large internal heat sink but that is sort of stupid since it just wicks heat off into the interior of the sealed enclosure.  I am thinking that I will need to scrape the plate amp area off to bare metal and use Artic MX-4 thermal compound to join the heat sink and the plate amp together.  Has anyone done this to a Legend?  These things are going to my son in college so I'd like to do a little preventive maintenance before they get torture tested.  I do expect them to blow sometime in the future but would like to prolong the event.

Edited by Istari
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Yes those are diodes. Why Mike thinks they are zeners I don't know. Both regular small switching diodes AND zeners can come in that same package. How to check: Unsolder one end then using "diode" function on your multimeter read diode in both polarities. In one direction it should it should read about 0.6 volts, in the other it should read much higher or open

Edited by babadono
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Has anyone put an external heat sink on the Epik Legend plate amp?  It has a large internal heat sink but that is sort of stupid since it just wicks heat off into the enterior of the sealed enclosure.  I am thinking that I will need to scrape the plate amp area off to bare metal and use Artic MX-4 thermal compound to join the heat sink and the plate amp together.  Has anyone done this to a Legend?  These things are going to my son in college so I'd like to do a little preventive maintenance before they get torture tested.  I do expect them to blow sometime in the future but would like to prolong the event.

The heat sink is mounted fast to the plate amp. The paint is off the plate amp, and thermal compound is indeed used.

 

IMO, the best preventative measure would be to add a low watt fan inside blowing on the 2 MOSFET's. Just the circulation inside the sub will give relief to the components that get hot. This is part of what I did in my Klipsch Promedia Ultra 5.1 sub. There are simply hotspots in some amps. I just snapped a couple thermal pictures of the Promedia which show external temperature. There is a fan inside blowing right on the hot spot.

Here is the top of the Promedia sub. It has been on all day. The hottest spot is under 80 degrees. The ambient temp under the desk is about 60 degrees. 

hEsOKPZl.jpg

Here is the hottest part of the sub. The back of the plate amp itself at 91.4 degrees. As you can see from the first picture, the heat is being spread throughout the speaker, but the rear plate is indeed sinking the heat to the outside.

FT13VLal.jpg

MKbl6RNl.jpg

Edited by mustang guy
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Yes those are diodes. Why Mike thinks they are zeners I don't know. Both regular small switching diodes AND zeners can come in that same package. How to check: Unsolder one end then using "diode" function on your multimeter read diode in both polarities. In one direction it should it should read about 0.6 volts, in the other it should read much higher or open

I have removed all diodes. I tested them and they all test open one way. I wrote down the specifics, but that is at the shop and I'm at home. The bottom line is none were shorted or they wouldn't have had an open lead either way.

 

Craig,

 I can't really tell by your pictures. Is that all burn on the circuit board traces or did something leak out of that black can that is probably an electrolytic capacitor?

                           Eric

The electrolitic in that position test good (about .14 on the ESR). You can see that in the pics on the previous page. The discoloration is the glue these guys used on the circuit board. It burnt and discolored.

I no longer have a computer at the shop, but the next time I am down there, I will grab that data on the diode tests and post it here.

Edited by mustang guy
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I believe the trick is to get the heat OUT of the box, not just circulating within the box.  Attaching a large heat sink on the outside of the box, after proper preparation of the outside surface of the plate amp and adequate thermal paste should help more than an internal fan.  That's going to be my direction.

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I believe the trick is to get the heat OUT of the box, not just circulating within the box.  Attaching a large heat sink on the outside of the box, after proper preparation of the outside surface of the plate amp and adequate thermal paste should help more than an internal fan.  That's going to be my direction.

That is a really good idea. We had a discussion about that very subject this summer. 

 

Another thing could be to pipe the heat out either by solid copper pipe or liquid cooling. These are extreme ways and frankly would depend on what you have laying around and how handy you are.

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  • 11 months later...

Well, it took a while.....

 

My Epik Legend amps did not die but I did perform some preventive maintenance on them before they gave up the ghost.

 

I removed the amps and replaced the seemingly failure prone FETS and the four large caps that make up the power supply.  While reassembling the amp I also left off the large silicone covers for the FETS but I put sleeves over the leads so there wouldn't be any arcing to the heat sink.  The amount and quality of the silicone grease used by the manufacturer for the individual FETs and other transistors plus the heat sink was a joke!!!!! When reassembling the electronic components to the heat sink I used Sil-Pads without any grease but for the heat sinks I used Artic MX-4.  It seemed to  have good reviews.  I was able to scour thrift stores and found an old Onkyo receiver that had a massive heat sink inside.  I was able to salvage it and cut it down to a size that would slightly overlap the internal heat sink.  Getting as much heat outside of the sealed enclosure was my goal, not just recirculating it within.  I was able to remove all of the exterior paint on the outside of the Legend amp and attached the external heat sink with thermal grease applied.  I had to get some longer screws that would go thru the heat sink, the back panel of the amp and into the internal heat sink. My pre and post heat measurement using a 26 hz tone shows a significant heat reduction.  hopefully this will result in longer life for the subs.  They are in a college environment now so if that won't test them to the max I don't know what else would.

 

July 13, 2017 UPDATE - Was able to post a picture of the heat sink addition.  They have been working very well, no failures at this time.

DSCN0067.JPG

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