MTX 405 Amplifier Smoking! Help - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th November 2009, 02:04 AM   #1
diyAudio Member
 
Join Date: Nov 2009
Default MTX 405 Amplifier Smoking! Help

Hey, I was hoping to get a little help with a smoking amplifier. I have an mtx 405 5 channel amplifier. Just today I was listening in the car at a normal volume and I started to hear a popping noise and when I looked at my passenger seat which is where my amp is installed under, there was a cloud of smoke. Thinking that the car was about to catch fire I pulled over and shut down power to the amp to keep anything from burning to badly. When I got home I opened the case and everything looked pretty nice but I did see a coil of green coated copper wire wound around something and this seems to be what got hot and smoked. It appears from looking at where it attaches to the board that one of the wire leads is broken. Is this an easy fix? it appears the wire is epoxied around something but I am unsure of how to proceed. The amp actually still plays just fine for about 5 minutes then starts to smoke. Any help I could get in repairing it would be great. Mtx said they no longer service this model but I would really like to get it working since it is hard to find a good, small 5 channel amp. Ill post some links to the pics of the part that I think is bad or damaged.
  Reply With Quote
Old 14th November 2009, 02:56 AM   #2
diyAudio Member
 
Join Date: Nov 2009
Ok, I really looked closely and under the wires and I see some caps that have bulged and exploded. That explains the gooey clear stuff on the case.
Here is a Link to the picture of the board.

http://i395.photobucket.com/albums/p...5/SANY0001.jpg
  Reply With Quote
Old 14th November 2009, 02:58 AM   #3
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
It sounds like you may be referring to the inductor for the class D channel.

Can you post a photo of the inside of the amp, the area where the component is located and a good quality close-up of the component?
  Reply With Quote
Old 14th November 2009, 03:46 AM   #4
diyAudio Member
 
Join Date: Nov 2005
I can't be sure from the picture, but it is possible that the green wire'd inductor is an input filter and the caps that smoked are the rest of the B+ filter. A simple problem like this would explain why the amp seems to run OK. Unfortunately the wire harness runs right over where what looks like one of the capacitors in the bank failed. If you find that only one capacitor vented then you can replace it and everything should be ok. If more than one capacitor bulged and/or exploded you may have something more serious wrong with the power supply and will probably take an experienced tech to fix.
  Reply With Quote
Old 14th November 2009, 04:04 AM   #5
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
The component with the green windings is the output filter for the class D amp. This inductor and the capacitors that have apparently blown remove the carrier (rail to rail square wave) from the class D amplifier's output.

Many of the MTX amps that used this type of inductor had problems with shorted windings. The windings tended to short where the terminal winding met the rest of the windings. This caused the capacitors to fail in those amps.

If the outputs haven't failed (they are probably OK since it's not drawing excessive current/blowing fuses), all you'll have to do is replace the blown caps (replace all in the group), insulate and resolder the inductor.

When you reinstall the inductor, you should place a drop of adhesive (Goop or similar) at several points at the base of the inductor. Don't completely fill the area under the inductor. It will make it very difficult to remove it if there is another problem in the future.

You MUST remove all of the electrolyte (gooey stuff?) from the amp. It's corrosive and conductive and will cause more damage if it's not removed completely.
  Reply With Quote
Old 14th November 2009, 04:51 PM   #6
diyAudio Member
 
Join Date: Nov 2009
Default Pics of the Caps

Here is a link to the swelling caps that blew up and the clear stuff that came out of them.

http://i395.photobucket.com/albums/p...5/SANY0006.jpg

http://i395.photobucket.com/albums/p...5/SANY0004.jpg
  Reply With Quote
Old 14th November 2009, 05:18 PM   #7
diyAudio Member
 
Join Date: Nov 2005
Quote:
Originally Posted by johnkean View Post
Here is a link to the swelling caps that blew up and the clear stuff that came out of them.

http://i395.photobucket.com/albums/p...5/SANY0006.jpg

http://i395.photobucket.com/albums/p...5/SANY0004.jpg
That is an aweful lot of capacitance for a class D output filter, if that is what Perry is saying it is. In any case you'll need a pretty beefy iron to desolder that inductor and clear the short, if that is what happened.
  Reply With Quote
Old 14th November 2009, 05:36 PM   #8
diyAudio Member
 
Join Date: Dec 2005
Location: Northern California
I have seen this before and those are 22ufd NON-polar caps and they are dust.. I also have replaced them before and had the amp go right back into safe and proper operation. They use a large number of them to add up to a number somewhere just over 100ufd NON-polar value. I think it was a size related issue as to why so many and so small. These caps can be tough to find also, at least I had fun locating enough of them to repair two of these a few years ago..
So this is a common issue I have seen on several occasions. And this repair could be as simple as just replacing all of those blown caps and restoring the filter section to normal operation...
  Reply With Quote
Old 14th November 2009, 08:52 PM   #9
diyAudio Member
 
Join Date: Nov 2003
Location: Louisiana
1moreamp:
I think these may be polarized caps. I can't remember ever seeing non-polarized caps in an MTX amp. If you look between the wires of the first photo, I think you can just see the negative markings on the caps.

Andrew Eckhardt:
Some class D amps use as much 330uf across the outputs. One example is the old MTX 81000D. It had four 330uf in series parallel across the output.

johnkean:
Don't lose the thermal pad that's on the cover. It's needed to help sink the heat away from the inductor and into the top cover of the amp.
  Reply With Quote
Old 14th November 2009, 09:16 PM   #10
diyAudio Member
 
Join Date: Nov 2005
Quote:
Originally Posted by Perry Babin View Post
Andrew Eckhardt:
Some class D amps use as much 330uf across the outputs. One example is the old MTX 81000D. It had four 330uf in series parallel across the output.
I guess for a sub channel it wouldn't be that surprising.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Zen V4 Smoking Q5 Diomedian Pass Labs 6 15th November 2005 02:46 PM
amp smoking biznatcher Car Audio 5 13th September 2004 11:48 PM
Smoking Amp jkramer Solid State 15 28th August 2004 04:17 PM
Smoking Amplifier jkramer Solid State 0 23rd August 2004 02:37 PM
DOZ smoking? Kari Solid State 8 1st February 2004 02:40 PM


New To Site? Need Help?

All times are GMT. The time now is 11:46 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2