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Old 25th February 2012, 09:10 PM   #1
diyAudio Member
Join Date: Feb 2012
Default MTX Thunder 81000D Problem

Hi I have a MTX thunder 81000D thier is a high pitched whining sound comming form the transformer but I was getting sound out of the board and when I pushed on the board it would go away.

With the whining sound the output signal was not a normal subwoofer signal.

Once I pushed on the board the signal was back to normal so I figured it was bad solder connections.

I resoldered the amp, I still have the same problem then somthing smoked but since im using a variable psu it protected the amp right away.

I started trouble shooting but without a schemtaic its hard.

I replaced 2 SMT's q264 and q263. I still have the same problem.

Im getting -70 and +70 volts from the fets. LED238 is on.

I checked chip TL494C im getting a sawtooth signal and the square wave signal to the fets is not much of a square wave it is a cross between a sine and a square.

Anyway Im kinda stuck without a schmatic at this point. So any help would be great.
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Old 26th February 2012, 11:39 PM   #2
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Join Date: Nov 2003
Location: Louisiana
If you can push on the board and make the fault come and go, you need to keep doing that until you find the component that's causing the problem.
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Old 26th February 2012, 11:50 PM   #3
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I did thats when a resistor or surface mount transistor smoked and now I cant get anymore sound out of it even after I replaced the bad smt's.

No other componenets look bad.

Do you happen to have a schematic for this amp?
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Old 27th February 2012, 09:46 AM   #4
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Join Date: Nov 2003
Location: Louisiana
Are you unsure whether the component was a resistor or a transistor?

I don't have any schematic that I can distribute.
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