It seems that my AVRISP mkII programmer died in a strange incident. It was connected to my computer via USB cable and to a custom board which hosts an ATXMEGA32A4U via its 6-pin programming header. The on-board connections for the programmer are according to Atmel's E-Schematic-Checklist (sect. 4).
The AVRISP stopped working (all lights went off) as I connected the board's power supply (an on-board LDO regulates the supply voltage to the 3.3V required by the microcontroller). Apparently, when the programmer is inactive there is some pull-down on the reset line, therefore the ATXMEGA at first seemed dead too. However, after disconnecting the programming cable the ATXMEGA resumed operation. It still works flawlessly and the LDO delivers 3.3V as expected.
After the incident I had no power on any of my computer's USB ports, therefore I powered down my computer, disconnected and reconnected mains power, which returned power to the USB ports. But as I connected my AVRISP it still showed no reaction (no power loss on the USB ports this time though). The OS did not even detect connection of a USB device, as dmesg did not report anything (note: this is on Linux).
I switched the programmer's USB cable, but that did not help. I opened the case to see if the AVRISP has any visible traces of damage, but it looks fine, as far as I can tell. Here is a picture of it (USB connector on the left, 6-pin programming header on the right):
Is there anything that can be done about this AVRISP or must I assume that it is damaged beyond repair? And what might be a likely explanation of this strange death?
EDIT: As suggested by Raj I have measured the voltage levels in what seems to be the power supply section of the device. In the above picture, the traces marked in red carry 5.05 V, everything else in the vicinity is at 0 V. It seems that the IC close to the lower left corner is an LDO which is defect. The package reads "BDR 391 ADFX", does anyone have an idea which device this might be?
EDIT 2: As suggested by Tom Carpenter I have bypassed the defective dc-dc converter, however now the supply voltage drops to 4.5 V and the device indicated in the picture quickly gets very hot.