Specifications

CA10 Course Notes
Sharp Electronics (UK) Limited
CE Technical Support Group Page 15
Protection circuits
There is a protection input on IC101, pin 77 ( PROT ) which causes the set to shut down should there be
a fault with the audio output stage.
When the audio output is operating correctly, the feed to the loudspeaker will have an average DC level of
zero volts. If an imbalance were to occur whereby the signal became predominately more positive or
negative, this could lead to failure of the audio output devices or loudspeaker. To alleviate this possible
problem, the circuit shown below is used to turn off the set should the situation arise.
Figure 14 : Audio Protection Circuit
Under normal conditions, both Q302 and Q303 are turned off and the voltage present on pin 77 of IC101
is held high by the 3k3 pull up resistor R141. Should one of the outputs go more positive, then the DC level
developed across C357 will increase. If this increase exceeds 0.6V, then Q303 will turn on, pulling down
pin 77 and shutting down the set.
If one of the outputs were to go too negative, then the charge on C357 would drop, if this drop is greater that
-0.6V then Q302 will conduct on pin 77 will be pulled low. Thus the set would shut down.
Software reset
As with the previous large screen chassis, the NVM is down loaded with its default information when the set
is first powered up after manufacture. This means that whenever a NVM is ordered, it will be the same for
all types of chassis ( previous NVM’s have come pre-programmed for the receiver in question ).
If the information within the NVM is corrupted or settings/adjustments can not be made, then it is necessary
to re-initialise the NVM. This is done using the following procedure.
1. Enter the service mode by pressing the channel down and volume up buttons on the front
of the receiver, while turning on the mains power. Note that the two buttons have to be
kept pressed until the receiver turns on.
2. Select the NVM position 00.
3. Set this location to 01.
4. Store the information by pressing the stand by button on the remote control.
5. Turn the set off at the mains.
6. Turn the receiver back on. It will take about thirty seconds for the receiver to start up as
the microprocessor is down loading the information into the NVM.
Some settings may need sight adjustment as the preset values are based on no tolerance settings , in
reality some will vary. Note that the above location of 00 is for the CS chassis type, to date this location for
the CA chassis is unknown. Please consult your Technical Liaison Officer for more details.