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My solution was to make a little daughter circuit board with a -5VDC generator circuit so that the shunt N channel MOSFET could be removed. Other more astute readers may be able to get the 220uH inductor off the board, open it up and re-wind it with new wire. I could not open up the special surface mount ferrite core used for the inductor as it was cemented together and not being able to obtain a suitable replacement core I made a rather drastic modification as a "work around" for the problem. The circuit is robust in that if an overload occurs the LTC1771 will limit the peak current and the ON time duration and this is what was happening with my unit. The specialty switched mode power supply IC is a LTC1771 device which is essentially designed for "current mode" of operation with a second voltage feedback loop. The internal power supply uses a series and shunt P channel and N Channel MOSFET transistors respectively, to obtain a stablised +4.8VDC and -4.3VDC power rails. Once heated up it would continue to work correctly until powered OFF and left to cool down whereupon it would fail to start up again. The fault turned out to be a shorted turn on the internal switched mode power supply series 220uH inductor that would go away once it was heated gently. The fault symptoms are: The internal RED SPDIF optical digital audio output LED is lit but the power, CMSS and audio mute LEDS are all OFF and the unit is not working. Faulty Creative Sound Labs SB0300 24bit external USB sound device.