Boston Soundware XS 5.1 Subwoofer Output MosFETs shorted again ！What & Why?

[Peter Qiu]

Boston Soundware XS 5.1 Subwoofer Output MosFETs shorted again ！What & Why?

Per the above title....

After replacing MosFET IRF540N at location Q10 and Q11.....MosFETs shorted again and 800mA Fuse blown when I powered up the Subwoofer.

Does anyone encounter this kind of problem?

There are presence of DC Power Supplies (+33V, -33V and +21V, -21V) at Switching Mode Power Supply Board connectors (CN2 and CN3).

Any suggestions on where can I find the schematics ?

Thanks in advance.

Peter。

 

[USRFobiwan]

I have the same sub i think, do not know if its the same problem but its dead, so I unscrewed the amp-plate to poke around with my multimeter and the whole print has glue all over, it's a mess so I gave up. Do you have any type indication so i can compare and see if it has the same problem on Q10/11?

 

[bullittstang]

Did you check any of the other resistors and transistors or did you just replace the power transistors?
Generally the power transistors will take out at least the Gate resistor, but could also damage the Source resistor. Also standard repair technique to go back one level back, so if the Power MOSfets burned, you should replace the driver transistors, even if they test good, because they would have had all that current dumped into them.
If you spend the time to take it apart and repair, a few bucks to replace 2-3 drivers is well spent in my mind.