Turns out my problem lies in the fact that I'm splicing power off the Nokia AC-4E adaptor to feed into a 5VDC regulator to serve as the USB power. The Nokia AC-4E adaptor doesn't supply a consistent voltage when plugged into both the Nokia and my kludged on 5V regulator ( LT1521-5). In particular, the adaptor's output voltage alternates between 6.3VDC and 4.5VDC in a square wave pattern. The duty cycle of the square wave depends on how much power is being drawn. The problem is then that 4.5VDC is insufficient for USB. So, the easiest solution I can think of is to replace the Nokia adaptor with a beefier 5VDC adaptor. My question now is, what is the maximum input voltage from the charging adaptor the Nokia 770 can handle? Note that almost all AC->DC converters actually output a higher voltage than indicated on the packaging. Thanks. -TM-