DC to DC Converter Startup
With the media receivers main power switch turned on, the power supply only outputs the
5v line to the main CPU and the SR UP input line to the display panel. When the standby
key is pressed on the remote or plasma panel +5 volts is sent from the display on the SMPOW
line to the relay driver Q705 in the main power supply. The relay driver Q705 turns on the main
+10 volt line supply to the DC to DC converter. At this time the main CPU is also checking the
HDCP Key data on the SDA and SCL lines. If the Key data received is correct, the main CPU
sends two signals to the expander IC1503 (150ms after the SMPOW signal started the +10 volt
supply). The expander IC then sends two signals to the DC to DC converter IC1701 and all DC to
DC converter circuits start up. When the converter outputs come up the +5 volt CCKM signal is
sent back to the plasma display. The outputs from expander IC1503 are the two voltage offset
information lines needed in order for IC1701 to function. As stated in the power on procedure,
every 128 frames the Key data is checked by the Main CPU (IC1) and will shut down the DC to DC
converter if incorrect.
