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Boston PV600 subwoofer blowing MOSFET

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abundant2

New Member
Hi there- A newby to the site. :)
I have the Boston PV600 subwoofer and it keeps blowing the MOSFET (sometimes the fuse as well if both MOSFET shorts out).

Replaced the MOSFET (complementary pair IRF640 and IRF9540) and will work for mayby 8 hrs or so and blows again.
Have checked the gate resistors etc and they are all ok.

Any thoughts what I should do - sorry I do not have the schematic and appreciate it if anyone out there has it.

thanks a million for any help here.
 

hyedenny

Active Member
Does it sound normal when it's working? Are the MOSFETs overheating before they blow?
Check your power supply, and check for shorted electrolytic caps.
That's my 2 cents without any other info!
 

crutschow

Well-Known Member
Most Helpful Member
How hot the MOSFETs get is a critical thing to determine.
 

abundant2

New Member
When operating, the mosfet are inside the unit. Will try and test it when it is opened up and see how hot it gets.
Also was thinking of parallel 2 mosfets to share the load. Anyone has tried this?
 

abundant2

New Member
Another option i am thinking of trying is to bring the mosfet to mount it on the outside of the box so it gets better cooling (rather than sealed in the subwoofer).
 

tomizett

Active Member
Yea, agreed - it should work as designed. There must be something a bit subtle wrong.
Does it fail only when it's being driven, or just switched on idle?
I presume these transistors are located in a class-D output stage - am I right? As always, pictures, schematics or traces of circuits will always be helpful.

How hot the MOSFETs get is a critical thing to determine.
This will help us work out what's going wrong. Just be careful of high voltages (and temperatures) while you're probing around.
 

unclejed613

Well-Known Member
Most Helpful Member
i can't find a schematic for it, but my best guess is it's an analog amplifier and not a class D amp. check carefully by pushing the woofer cone in to see if the voice coil is rubbing somewhere. class D amps don't usually have complementary output devices, so i'm fairly sure this is an analog sub amp. a picture of the amplifier PCB would be helpful.
 

tomizett

Active Member
class D amps don't usually have complementary output devices
True, although I've seen some that do.
Good advice on checking the driver, certainly.

If the OP's still here, is there any chance of a picture? I think they may have given up on this....
 
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