2.7 LEDs
Sheet 8 of SD254175
The amber and green LEDs on the DSP board serve to provide a wealth of information about the
status and operation of the DSP board. The following is a summary of the various possible states
of the LEDs and a functional description of the state(s) represented.
•
Green LED: The green LED serves a dual purpose: general system health and serial data re-
ceived. The green LED will blink once per second with a 50% duty cycle (i.e. on for ½ second, off
for ½ second) if the system booted and is running normally. If the unit is in the SmartSpeaker "Off"
condition, the green LED will blink briefly (approx. 0.1s ON time) once every 5 seconds.
•
The green LED will also toggle whenever a serial data byte is received. This will interrupt the
normal 1 second blink rate. The green LED blinking faster than 1 Hz usually indicates that it is
receiving serial communications.
•
Amber LED: The amber LED serves to signal 3 conditions: power applied/boot status, S/PDIF
status and clipping status. When power is first applied the amber LED will light briefly. If the PROM
FLASH checksum is incorrect or hardware does not pass power-on self test, the green LED and
amber LED will alternately blink at approximately a 5 Hz rate. If the green LED is blinking at its
normal, 1 Hz rate, a blinking, 1Hz amber light indicates that there is no valid S/PDIF signal
present: If the amber LED is off while the green LED is blinking normally, then valid S/PDIF is
present and being received. Finally, if the amber LED will briefly blink (in this case, only when valid
S/PDIF is present) when the satellite amps are clipping. This should only occur when playing the
system at very high levels.
2.8 Master Reset and Watchdog Timer
Sheet 8 of SD254175
U602 functions as the master Reset controller and watchdog timer. This part will briefly issue a
Reset to the Sharc when the +3.3V rail first comes up or if the 3.3V rail drops below 3.08V. The
part also contains a timer which will cause a Reset to occur approx. every 1.5 seconds unless the
WDI input to the IC is toggled at least once during each 1.5 second cycle. This is useful in the
event that the Sharc would become "lost" in program execution, which would prevent it from "pet-
ting" the watchdog every second, and the system would get Reset and recover.
2.9 Tracking Power Supply Control Output
Sheet 3, 8 of SD254175
As part of the DSP signal processing, the maximum level of any of the six audio channels in a
256-sample block is computed. This value is then translated into the minimum required power
supply rail voltage needed by the power amplifiers to reproduce that block of audio without clipping
or distorting. The Sharc adjusts the duty cycle of the pulse-width modulator output DT1B (pin 23)
of U4 appropriately so that the resulting "DC" voltage after the RC lowpass filter formed by R209/
th
217 and C203 is 1/10
the Power Supply PCB through J604, pin 12. When there is no audio output (or relatively low
levels), this output should be at 0% duty cycle, or approx. 1.3V as measured at PSC_PWM.
Theory of Operation
the required power supply rail voltage. This signal, PSC_PWM, is sent to
PS18/28/35 Troubleshooting Guide
15
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