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Old 7th August 2013, 09:24 PM   #1
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Default Faulty MTX 500D

I hate to hijack this thread 4 years after it started, but I have one of these MTX 500D's and I need to repair it. There are a few burned out MOSFETS and two resistors that are as black as coal, making it difficult for me to identify what there are so that I can replace them. Does anybody have a diagram for this board?
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Old 8th August 2013, 06:37 PM   #2
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Old 8th August 2013, 07:44 PM   #3
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You should know, before you begin, that these amps have a lot of problems.

Which FETs and resistors are burned (give the circuit board designation).

IF you haven't done so already, read the basic amp repair page (in its entirety, even the parts that you think are irrelevant).
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Old 9th August 2013, 05:12 PM   #4
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Thank you for the link, it's very informative. FET203, 202, and 204 are blown to bits. FET201, REC202, and REC201 appear to be shorted. The four FET's on the other side of the board seem to be operational. Are the blown transistors the power transistors?
As for the resisters, I can't make out the board designation, but here are some pics, I hope they help.
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Old 9th August 2013, 07:25 PM   #5
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Those resistors are 150 ohms.

When these fail, it's likely that many other components have failed. Are you repairing this amp because you need a working amp or because you're interested in learning to do this type of work?
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Old 9th August 2013, 11:34 PM   #6
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Actually, it's a bit of both. I got the thing at a garage sale for $10, I plugged it in to my subs and it worked, but I didn't use it much. I then played with it a bit too much and shorted something. I am going to Purdue in a few days to study Computer Engineering, so most of my interest lies in the knowledge I could gain from fixing such a thing. Electronics fascinate me, and I am constantly learning new things on the internet. I won't mind replacing things, but if it gets too expensive I better leave it for now. If the resistors and transistors don't fix it, what do you think it will cost to get it working?
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Old 10th August 2013, 12:56 AM   #7
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Parts will likely cost about $20 (not including shipping). There is a chance that it won't be repairable so bear that in mind. Expect to spend several hours working on it.

There are several 500D threads in this forum. Do a search and read all of the older posts.
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Old 10th August 2013, 02:35 AM   #8
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Quote:
Originally Posted by Perry Babin View Post
The regulators failed regularly in these amps because they ran too hot. When they failed, they often destroyed all of the op-amps in the amp. If you don't have any shorted outputs or power supply FETs, the regulator damage may be the only thing you need to repair but expect at least several hours work and expect to replace at least about 20 parts. Refer to the following:
http://www.bcae1.com/temp/mtx500dregulatordamage01.swf
Should I start out with following these directions?
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Old 10th August 2013, 04:09 AM   #9
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Read all of the 500D threads. The information there is only part of what you need to know.

I don't know if this was stated earlier but the rectifiers are likely OK.
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Old 18th August 2013, 08:11 PM   #10
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Okay. I read all of the other threads and none of them pertain exactly to this problem. I'm going to start with these resistors. 150 ohms, but how many watts do they have to handle? Also, you recommend using 390 ohm resistors. Does this decrease the performance of the amp? Won't the resistors heat up too much?

Last edited by Chuppster; 18th August 2013 at 08:22 PM.
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