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Switching Power Supply Short

gerryt

Feb 5, 2021
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Hi all, I am trying to find a short in a SMPS for a subwoofer. It keeps blowing fuses as soon as the 120 AC power is turned on. The NTC Thermistor was damaged when I took a look at the board. Any suggestions as to what the most likely cause of this is? Thermal Resistor.JPG
 

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danadak

Feb 19, 2021
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Feb 19, 2021
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Are the two large caps bulging at top ? cant tell from pic but if
they are could be damaged. When caps go they take other parts
with them.

Look on youtube, lots of videos repairing SMPS, troubleshooting methods,
hints.....

Regards, Dana.
 

Bluejets

Oct 5, 2014
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rectifier diodes, capacitors, switcher ic, mosfet switchers....all could be suspect but you need to isolate and test each.
 

gerryt

Feb 5, 2021
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Thanks for your words of wisdom. Checking each piece one at a time, so far have found a faulty resistor.
 

gerryt

Feb 5, 2021
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The resistor's resistance value is supposed to be 100K and it is 1 milli ohm. I have also found two MOSFETs that were not working when tested on the multimeter.
 

Bluejets

Oct 5, 2014
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I doubt you have a meter to measure down to 1 milliohm......do you mean 1 megohm?....measuring has to be out of circuit ....
 

gerryt

Feb 5, 2021
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Thanks for the correction on this. Yes, measured it again, it is 1 megaohm out of circuit, the specs on the chart say it should be 100Kohms
 

Bluejets

Oct 5, 2014
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What chart...???
Perhaps post what you have here would be a good start.
 
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