Specifications

CA1 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support GroupPage 54
CA1 Power On Control
During the stand by mode, IC1001 ( main microprocessor ) is supplied with the standby +5Va from the
chopper stage on pins 11 and 37. This supply is generated by the series regulator transistor Q704 from the
supply generated by D712 off pin 9 of T700.
Figure 47 : CA1 Power On Control Circuit
To enable the set to turn on, pin 4 of IC1001 goes low, which turns off Q1007 and allows its collector voltage
to rise up to 5.7V ( set by the shunt regulator comprising of R712, D715 and D723 ). Series regulator Q708
turns on and provides the +5Vb running supply. At the same time Q501 is turned on and Q706 also, this
provides the +10V supply to the frame output stage. Once these supplies have come up, the
microprocessor will allow the line, then frame stages to start up.
A feed from the collector is also taken to the base of Q305 via R316 and C308, this is to prevent any sound
from emanating from the loudspeakers during start up. C302 and R306 will drag down the audio signal
momentarily as the charge on C308 builds up. This muting action will only last a few seconds. Note that
when the set is taken back into standby, D301 will rapidly discharge C308 so if the receiver is turned on
again quickly, the same action will take place.