I am repairing a QSC Powerlight 6.0 PFC amplifier and the problem is in the
chopper circuit of one of the the power supplies. Q2, the IXFN55N50 Hi Perf
MOSFET, an SOT-227B package device, had a rather spectacular end of life
event. Fortunately the audio rack's breaker tripped before damage could
spread to catastrophic damage levels.

I'm in the process of determining the health of related components, but at
least one of the IXFN55N50 devices has become carbonized and one terminal
welded itself to the mounting screw.

I'm in search of a supplier of this device, in the US, for small quantities
for repair and maintenance purposes. Perhaps a maximum order of 8 devices,
depending on price.

Who sells these devices in the US? My Googling takes me to a lot of Chinese
suppliers and huge lot quantities.

If someone is familiar with a US supplier for these, I would greatly
appreciate hearing from you. I'll check back here periodically. Thanks.

--


Take care,



Mark & Mary Ann Weiss



VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
Hear my Kurzweil Creations at: www.dv-clips.com/theater.htm
www.basspig.com The Bass Pig's Lair - 15,000 Watts of Driving Stereo!
Business sites at:
www.mwcomms.com
www.adventuresinanimemusic.com
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Mark & Mary Ann Weiss wrote:

I am repairing a QSC Powerlight 6.0 PFC amplifier and the problem is in the
chopper circuit of one of the the power supplies. Q2, the IXFN55N50 Hi Perf
MOSFET, an SOT-227B package device, had a rather spectacular end of life
event. Fortunately the audio rack's breaker tripped before damage could
spread to catastrophic damage levels.

I'm in the process of determining the health of related components, but at
least one of the IXFN55N50 devices has become carbonized and one terminal
welded itself to the mounting screw.

I'm in search of a supplier of this device, in the US, for small quantities
for repair and maintenance purposes. Perhaps a maximum order of 8 devices,
depending on price.

Who sells these devices in the US? My Googling takes me to a lot of Chinese
suppliers and huge lot quantities.

If someone is familiar with a US supplier for these, I would greatly
appreciate hearing from you. I'll check back here periodically. Thanks.

Check QSC's website www.qscaudio.com IIRC. The chermatics are there.

The IXYS devices are probably not the ones originally specified and they're
just 'commondity' N-ch mosfet or IGBTs most likely.

Graham

On Sun, 21 Jan 2007 05:30:33 GMT, "Mark & Mary Ann Weiss"
wrote:

If someone is familiar with a US supplier for these, I would greatly
appreciate hearing from you. I'll check back here periodically. Thanks.

The IRF FA57SA50LC should be compatible, and can be bought at Digikey
http://catalog.digikey.com/scripts/d...=FA57SA50LC-ND

"Ole Geisler" wrote in message
...
On Sun, 21 Jan 2007 05:30:33 GMT, "Mark & Mary Ann Weiss"
wrote:

If someone is familiar with a US supplier for these, I would greatly
appreciate hearing from you. I'll check back here periodically. Thanks.

The IRF FA57SA50LC should be compatible, and can be bought at Digikey

http://catalog.digikey.com/scripts/d...e=FA57SA50LC-N
D

Thanks for bringing this upgraded version to my attention. The price is
considerably less than the other device, too. Since these appear in parallel
pairs, I'll plan to replace its sibling when making the repair.
Oddly enough, Digi-Key is out of stock on this item as well... perhaps some
other supplier might have ready stock, hopefully.

If someone is familiar with a US supplier for these, I would greatly
appreciate hearing from you. I'll check back here periodically. Thanks.

Check QSC's website www.qscaudio.com IIRC. The chermatics are there.

The IXYS devices are probably not the ones originally specified and
they're
just 'commondity' N-ch mosfet or IGBTs most likely.

Graham


Already downloaded it before I bought the amps (to study the circuit
topology) so I could research the build quality of the design.
These amplifiers have an outstanding reliability track record, based on the
many sound touring company owners I've spoken with last year, when I was
deciding which amps to purchase. However, this one failed while turned on,
but idling. QSC tests their amps by shorting the outputs, driving it to
clipping, and blocking the air intakes and then retesting them to see if
they meet spec, according to their marketing materials. So I'm hoping that
this was a bad run of MOSFETs. I still often wonder why these fail when not
under stressful operating conditions. Impurity in the die at manufacture
(unclean cleanroom?) bad seal on the plastic case? Dendrites growing across
the p-n junction over time?
Another thing I noticed was the use of copper 'ribbon wire'--flat copper
strapping for the hf power supply wiring to and from the main switching
transformers--which was insulated with thin Kapton or similar tape. There
was a section on the bottom that looked like the Kapton insulation had
burned through, causing me to wonder if there was an arc between two
adjacent (but touching) conductors, due to the way it was manufactured.
The schematic actually calls for the IXYS devices by part number--that's
where I got the p/n from.
Fortunately, I killed the power before significant damage occured. Some
smoke and soot around the viscinity. I washed the board as best as possible.

On Sun, 21 Jan 2007 21:09:59 GMT, "Mark & Mary Ann Weiss"
wrote:


"Ole Geisler" wrote in message
.. .
On Sun, 21 Jan 2007 05:30:33 GMT, "Mark & Mary Ann Weiss"
wrote:

If someone is familiar with a US supplier for these, I would greatly
appreciate hearing from you. I'll check back here periodically. Thanks.

The IRF FA57SA50LC should be compatible, and can be bought at Digikey

http://catalog.digikey.com/scripts/d...e=FA57SA50LC-N
D

Thanks for bringing this upgraded version to my attention. The price is
considerably less than the other device, too. Since these appear in parallel
pairs, I'll plan to replace its sibling when making the repair.
Oddly enough, Digi-Key is out of stock on this item as well... perhaps some
other supplier might have ready stock, hopefully.

You can buy it at www.irf.com directly

Thanks for bringing this upgraded version to my attention. The price is
considerably less than the other device, too. Since these appear in
parallel
pairs, I'll plan to replace its sibling when making the repair.
Oddly enough, Digi-Key is out of stock on this item as well... perhaps
some
other supplier might have ready stock, hopefully.

You can buy it at www.irf.com directly

I got lucky. After digging through the QSCaudio web site, I discovered that
they sell a power supply restoration kit, which includes ALL of the devices,
plus diodes, op-amps and resistors, etc, for less than it would cost to buy
four of these devices from a distributor. And I called QSC and they assure
me that they can ship in 48 hours. If all goes well, the kit will arrive
before the week ends. Of course, the tech there tried to talk me into
sending the amplifier back to them for service, but the freight costs alone
would be more than the repair cost. :-) I convinced him that it will work
out fine if I do the repairs in my own shop.
In a way, this amp is very similar to the circuitry and components used in
the Harris SX line of AM broadcast transmitters, which I service in my radio
engineering business. Only difference is that the transmitters run full tilt
100% duty cycle and run for the better part of a decade without a failure,
while this amp was idling when it failed.

While I've managed to order a repair kit directly from QSC, they keep
urgently pressuring me to send the amp in for recalibration.

I am replacing the chopper transistors, Q1-Q4 (Q2 is what failed) that drive
the primary of the transformer and you can find this circuit on page 12 of
this schematic, available from QSC's web site:
http://www.qscaudio.com/support/libr...werLight%20Ser
ies/pl6.0PFC.pdf

Frankly, I don't see where this non-linear device, replacement of such,
would necessitate a recalibration of the controller, since this is simply a
binary (on/off) process, chopping pulstating DC off the input rectifiers and
producing the initial 180KHz powerwave that gets split up and filtered on
the secondary.

Are the variations among the same part number IGBT so great that a factory
recalibration of the entire unit be performed, using "proprietary test
equipment and procedures"?

My impression is that there is little to nothing to adjust for--I'm just
replacing a switch with a new switch. Performance should be the same. Am I
missing something?


--
Best Regards,

Mark A. Weiss, P.E.
www.mwcomms.com
www.basspig.com
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