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Noise power supply switching Crown I-Tech T6000.

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mj15015 View Drop Down
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Joined: 16 July 2017
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    Posted: 16 July 2017 at 3:35pm

Hi everyone, Greetings from Argentina, I am an audio technician today I am repairing the power supply of the crown t6000 I arrived with a burned mosfet mmbf170 I replaced it and I kept walking but my doubt is because it makes noise the source? Is by the type of modulation of face (Phase Shift Modulation)? I have already controlled the whole diagram, capacitors ok, voltages +20 and -20 ok + 15v and -15 ok ref. 5v ok +180 Y-180 ok, SG3525 seems to be working well in the video the oscilloscope is showing pin 11 of the SG3525, someone who works and repairs any of these models I4000, I6000, I8000 can answer my question. I leave a link to the video where you can hear the noise; It looks like a spark jump but none of that is happening ...

 
 
 
 
 



Edited by mj15015 - 17 July 2017 at 2:58am
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U.Viktor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote U.Viktor Quote  Post ReplyReply Direct Link To This Post Posted: 17 July 2017 at 5:36pm
Without seeing the main power circuit it is impossible to say the exact topology and modulation scheme used in that power supply.
The MOSFET failed looks seriously undersized in that position, it is just a half-Amper FET , I would put at least 2-3A type there.
If you see these gate driver FETS making not only the gate clocking signal but also the full power for the isolated gate drivers across the gate transformer. Driving 3 or more of the power devices I guess @50KHz or more would needs larger FET for safe operation.
Otherwise the whole floating gate driver section looks utterly over-complicated, so many CMOS gates just for local UVLO when simple and more reliable integrated solutions exists since ages? Weird..
The SG3525 drives pair of gates and flip-flops looks "poor man's phase shift modulator" anyways :-)


Edited by U.Viktor - 17 July 2017 at 5:37pm
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