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Old 28th February 2009, 09:23 PM   #1
packer is offline packer  United Kingdom
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Default Pwm Class D Issues

I have an FBT MAXX 4a powered speaker which keeps blowing FETS (Q3).
Even with a lamp in series with the AC Line it shorts Q3, D5 & U2

SCHEMATIC HERE


All help would be be most appreciated
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Old 1st March 2009, 12:45 AM   #2
infinia is offline infinia  United States
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MOVED FROM CLOSED THREAD IN SOLID STATE FORUM

Hi
It looks like a Class D amplifier output stage.
It's basically a pulse width modulated power switch with a low pass filter.

U2 is a MOSFET driver with high side and low side gate drive.

Check Q4 and then ohm for any low impedance or shorts on the output.
If OK, check with O-scope after disconnecting the 60V drain supply.
EDIT>If the otherside is working, use it for a reference.

Cheers
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Old 1st March 2009, 10:59 AM   #3
packer is offline packer  United Kingdom
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@infinia Thanks very much for the assistance :-)

If i am understanding the PWM theory part correctly.
If the amplitude of the audio signal increases or decreases to the mark/space ratio of the waveform, do higher frequency's dictate the amount of on time and lower frequency's the amount of off time on the wave form?
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Old 17th March 2009, 05:34 AM   #4
b15075 is offline b15075  United States
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Default FBT MAXX 6a

Anyone know where I could find a schematic for an FBT MAXX 6a
I tried the 4a but it is a lot different. Any help would be greatly
appreciated.
Thanks
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Old 17th March 2009, 08:28 AM   #5
packer is offline packer  United Kingdom
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Morning,
Let me make a call to FBT today, I should be able to get that for you.
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Old 23rd March 2009, 04:39 PM   #6
packer is offline packer  United Kingdom
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Default Schematic request.

OK,
Finally got that schematic from FBT send me your email addy if you still need it. :-)
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Old 24th March 2009, 03:32 AM   #7
b15075 is offline b15075  United States
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Smile FBT MAXX 6a Schematic

Hi, if you could e-mail it to me at jt2130@yahoo.com that would be great . Thanks so much, really appreciate it.
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Old 24th March 2009, 01:47 PM   #8
fredos is offline fredos  Canada
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Me too please..I have 3 on a tablet for at least 6 weeks...fredos666@hotmail.com
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Old 24th March 2009, 01:54 PM   #9
packer is offline packer  United Kingdom
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Sure thing,
I will do it when i get back to the workshop tonight!
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Old 24th March 2009, 07:13 PM   #10
packer is offline packer  United Kingdom
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OK Guys,
Just emailed you both the Schematic. And if you need anything else let me know.
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