The CLASSiC DAC goes through a number of self-test routines at start-up and if these fail, it indicates the problem by flashing the LEDs. It also indicates invalid or unsupported digital audio data by flashing the sampling rate LEDs. Similarly, if the bootloader encounters a problem, it displays an LED flash code. These codes are explained below. 1) Bootloader If the bootloader fails, it will flash the 44.1kHz sampling rate LED and one of the input LEDs. This indicates the following possible errors: * flashing input 1, error: unable to initialise SD card (bad/incompatible card, unsupported/invalid partition table) * flashing input 2, error: unable to mount file system (bad/incompatible card, unsupported or corrupt file system) * flashing input 3, error: unable to open HEX file * flashing input 4, error: flash memory written but verify failed; check the correct HEX file has been used. If this persists you will need to re-flash the chip using an ICSP * flashing input 5, error: problem reading HEX file; check that the file is not corrupted * flashing input 6, error: HEX file contains invalid data 2) Main program power-on self test If the main program detects a problem at start-up, it flashes on of the input LEDs. The sampling rate LEDs remain off. The possible errors are: * flashing input 8, error: PLL1708 is not generating the expected frequencies on command. If this occurs, the PLL1708 is left enabled and you can check its output frequency if necessary. * flashing input 7, error: unable to communicate with CS8416. * flashing input 6, error: unable to communicate with CS4398. 3) Digital audio errors/status If the selected digital audio stream is not supported, the sampling rate LEDs flash or pulse in one of the the following patterns. * All sampling rate LEDs flashing: S/PDIF biphase or CRC error (usually indicates bad connection) * One sampling rate LED flashing: S/PDIF parity error or marginal signal; audio is otherwise valid * One sampling rate LED pulsing (alternating between bright and dim): valid audio signal with pre-emphasis * 44.1kHz & 48kHz LEDs flashing: DTS compressed audio data detected; output muted * 48kHz & 96kHz LEDs flashing: IEC61937 compressed audio data detected; output muted * 96kHz & 192kHz LEDs flashing: unknown non-PCM audio data detected; output muted 4) Other errors (SD card) If an SD card is inserted, LED8 pulsates while it is being read. If this continues for more than a few seconds, that suggests a bad or incompatible SD card. If valid WAV files are detected, input LED 8 turns on bright and playback begins (unless auto-playback has been disabled). If no WAV files are found on the card or it can't be read, LED 8 remains somewhat dim; if you switch to another input, it should go off in this error condition.