"Phil Allison" wrote in
:


This is a strange one, what do you think, Phil? I need your input.
Thanks buddy.


** Looks like that amp uses a SMPS ( switch mode power supply).

The whole thing is quite bizarre.

A powered sub woofer in a 9 inch cube - strewth !!

Let Sunfire do it, they have built that thing so it is fit for factory
service only.





....... Phil


I will tell you what, the magnets in the driver has got to be the
strongest magnet I have ever seen, dude. It is so hard to press the
diaphragm in with your fingers that it would take massive force just to
move it. I put screws for the unit in a very strong freezer zip lock back
and when I pull the bag of screws out, the screws stay stuck to the
magnet, the bag rips, and I end up with an empty, ripped freezer zip lock
bag. When I put the 9" cube with the driver in it near my computer to
take a deskcam picture for you, my monitor turns green and purple when
the darned cube is over 3 feet away! Not just a little green and purple,
but the whole image is massively discolored because of the strength of
the magnets used in this speaker. Bob Carver did publish a white paper on
his super subwoofers here if you are bored and want to read a bit about
just how this stuff is supposed to work:
http://www.sunfire.com/pdf/Sunfire_S...Whitepaper.pdf

No, it is not an smps, they had a word for it but I forgot what the hell
they called it, oh yeah, the power supply circuit utilized in this amp to
make tons of power but only supply what the amp needs at the time is
called "A Tracking Downconverter Circuit". To me is sounds pretty much
like the same **** with the triac but they found a new way of doing it.

I did use my meter and found that the two big caps. 1,000uF @ 200V are in
series and go down to the amp board. There is no "transformer to speak of
other than a small one on the small power board. The big caps get line
voltage, rectified directly to them and might even use a voltage doubler
configuration to end up with the 302 VDC that I observed across both
caps. Full wave rectification on 120 VAC house current yields about 160
VDC or so. The small transformer has small diodes with +12 and -12 volt
regulators on the board. Small standby current to run the low level and
turn on circuits, no doubt.

It looks like the common connection between the two big caps is speaker
ground. I think that the IRF640 MOSFETS (Datasheets here):
http://www.alldatasheet.com/view.jsp?Searchword=IRF640

Are part of this Tracking Downconverter Circuit and when the two large
output bipolar transistors blew, 2SA1302 & 2SC3181, they took out two of
the MOSFETS with them. This is all speculation as I have no schematic
because Bob Carver wants to keep that circuit as intellectual property.

So the 6 parts I need; 2 GMA4A fuses, 2 IRF640 MOSFETS, and 2 bipolar
output transistors cost maybe $25 or less, I will recheck for anything
shorted, open, or burned, then put them in and hope for the best. If it
works, great. If it smokes, then I lose the job and it goes back to
Sunfire for repair at the flat rate of $275.

Any last minute tips, Phil? Just plug it in and keep fingers crossed? Try
the light bulb or variac? What do you think? Thanks for sticking with me
on this Phil, because I really had no idea of how to proceed or what to
do about this situation and even just talking to another knowledgeable
person is enough to help one make up one's mind.

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