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Old 26th September 2007, 04:00 PM   #1
vr4 is offline vr4  United States
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Join Date: Sep 2007
Default MTX mxa8001 - Broken & fedup

Ok here is the story;

I purchased a brand new MTX mxa8001 a class d mono-block amplifier from circuit city about 2 years ago on sale. At that time i was driving an old civic hatchback and just didnt have the room for it, so it sat waiting for me to get a new car. I finally got a newer car a year & 1/2 ago, and set the audio up in it. I wired in this amp and attached to a smaller 10 inch sub- just to test to make sure all is well. I tested the system, and sounded great, for the first 5 min, then the 30 amp inline fuse for the power line blew, and i figured, man these monoblock amps draw alot of current.

I never replaced the fuse until now waiting for an enclosure i purchased from ebay to arrive. The ******* on ebay took 6 months to mail the enclosure so this further delayed the process of re-hooking up the amp to a speaker that could handel the power. So when i finially had all the pieces i went to hook everyhting up and my prized mxa8001 amp is dead.

- The amp -
When connected to power (with or with out ignition) it begins to get hot. Now, when further removed from everyhting else, meaning just connected to power and ground it gets hot. at no point does it output any signal, nor does it turn on. It just gets hot.

Upon inspection of the insides i am pissed. This was a brand new amp that was never run hard, nor run for more then 5 min. Now it is just another project.

I have a chared trace on one of the opening transistors. I believe that the heat sensor broke the circuit of the amp saving it from further destruction.

Question: anyone have any experience with these amps?
Besides the transistor, what else would be a good idea to replace. I am up at school and only have access to my sears style voltmeter - no osthelliscope.

Comments?

If this guy is swinging a hammer - thats what i want to be doing right now
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Old 26th September 2007, 05:52 PM   #2
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Location: Louisiana
I've never worked on one of these. From the only photo I could find online, it looks like a cross between the MTX80001D and the smaller 6500D.

Pull the clamps off of the larger transistors and post the numbers off of them? Only post the number common to all of them.

Set your meter to ohms and measure the resistance between the 3 legs of each transistor. If you find any single transistor or group of transistors that read near zero ohms, post the part number. Disconnect the power source from the amp before doing this. If it's still in the vehicle, pulling all of the fuses will be sufficient.

If you can, post a good quality photo or email it to me at babin_perry@yahoo.com. If you send me more than one photo, please send them zipped.
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Old 26th September 2007, 08:24 PM   #3
ppia600 is offline ppia600  United States
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Put some photos of it on the photobucket website and then copy it from there and then come here and paste it into a new post, if you can. I'm curious to see how those amps look inside. We used to sell them.
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Don't worry... you can always turn the gain down!
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Old 27th September 2007, 06:53 AM   #4
vr4 is offline vr4  United States
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Hey guys, thanks for the quick reply,\

i ment to post pics last ngiht - but it took a while for the original post to appear.

well here we go - high resolution

http://s234.photobucket.com/albums/e...t=IMG_3729.jpg

burnt transistor (it is the top left one )

http://s234.photobucket.com/albums/e...t=IMG_3726.jpg

http://s234.photobucket.com/albums/e...t=IMG_3725.jpg

http://s234.photobucket.com/albums/e...t=IMG_3721.jpg

this is the whole amp.


ok - i am going to go take some readings and post again
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Old 27th September 2007, 06:53 AM   #5
vr4 is offline vr4  United States
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Perry - that was really good advice. ive found that everyting seems to be matched ecept the transistor that i was suspecting.

it is the left one of the 2 in the top right. It had open continuity btwn all legs.

it is an FA323 FEP160TA - it looks ok - one of the legs looks a little burnt - but it has open continuity accross itself. there is a symbol on it --|< - >|-- that i interpret as meaning "ground live ground" - but i might have just made that up

the one next to it is u47332 byw51 (but i think this one is ok)

the rrest test ok. and nothing else looks bad on the board.

Now if transistor is the problem... what are some things that could have blown it?

thanks guys
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Old 27th September 2007, 07:10 AM   #6
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Those two devices are rectifiers. The symbol you drew shows that it's a negative rectifier. The other one is a positive rectifier.

It's possible the leg broke and it was arcing due to the intermittant contact and it looks burned. If the leg actually burned off, that means that enough current passed through it to melt the leads and that generally means you have a serious problem.

When it was getting hot, did you notice if it was getting hot on one side more than the other?
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Old 27th September 2007, 11:21 AM   #7
acid_k2 is offline acid_k2  Italy
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Quote:
Originally posted by Perry Babin
It's possible the leg broke and it was arcing due to the intermittant contact and it looks burned.
Maybe it IS burned... intermittent contact -> high peak current to charge power supply capacitors.

Maybe also a bad insulation between the tab of the rectifier and chassis

Perry, correct me if i'm wrong (I'm not an expert... )

Quote:
Originally posted by Perry Babin
If the leg actually burned off, that means that enough current passed through it to melt the leads and that generally means you have a serious problem.
I agree.
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Old 27th September 2007, 04:08 PM   #8
vr4 is offline vr4  United States
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Great input guys!

Quote:
Originally posted by acid_k2

Maybe also a bad insulation between the tab of the rectifier and chassis

I agree.
humm - i dont believe that there is any insulation at all. - Let me take more photos so that i am sure we are talking about the same thing.



The legs are not burned off. they are still connected to the "black housing". There is also zero resistance between between the three legs of the one chared rectifier (that i mistook for a power transistor).




the pictures are not as clear as i would like them to be. I will try again today in the daylight.

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Old 27th September 2007, 04:45 PM   #9
acid_k2 is offline acid_k2  Italy
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If there is a silicone/kapton/mica pad between device and heat-sink, the rectifier must be electrically insulated from heat-sink (chassis)

If there is zero resistance between ALL the legs, rectifier is in short-circuit (burned)
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Old 27th September 2007, 05:35 PM   #10
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Location: Louisiana
It appears to have a white sil-pad under it.

You need to remove the rectifier and check it again. Double-check the number on the rectifier. It's likely an FEP16DTA.

If the legs are not burned, it's likely that a strand of wire worked its way into the amp and fell across the terminals. Did you find any other tiny strands of wire in the amp?
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