DOWNLOAD Sharp 66FW-54H Service Manual ↓ Size: 6.05 MB | Pages: 80 in PDF or view online for FREE

DA100 (50Hz) Chassis – Article for Television Magazine 

In the case of an incorrectly operating or dead set, the Dolby Pro-Logic PWB can be ruled out by 
disconnecting it from the main PWB.  This is easily achieved by disconnecting the large multi-way cable 
from the main PWB.  The set should start up normally, but there will be no sound if the television has 
been set to external speakers. 

 
 
 
 
 
 
 

Sometimes the television may appear to be dead due to the failure of the Dolby Pro-Logic power 
supply.  Invariably Q1701 will have failure, the +/-17V rectifier diodes (D1708 and D1710) as well as 
some or all of the output devices – IC1302, IC1303, IC1304 and IC1305. 
Some problems are customer generated especially when it is related to user settings.  One of the most 
common is that the set is not configured for external speakers (no sound from the external speakers) 
or that the set has not been set up for Dolby Pro-Logic which results in no Pro Logic Function.  Refer 
to the operation manual for more information on this. 
There are differences between the Dolby Pro-Logic PWB fitted to the FW and GF range of television 
receivers.   The fundamental circuits are identical, however the sub-woofer speaker drive signal is 
taken from the MSP (IC305 pin 31) and not the Dolby Pro-Logic processor.   As the MSP is used to 
drive the sub-woofer drive IC, its impedance is different, which means that the matching circuit 
comprising of Q1304 is different to the FW models.  This also means that the software is different 
between  the  models.    The  GF  models  also  have  a  speaker  mounted  in  the  read  cover,  this  is  a  sub-
woofer speaker and is driven from the sub-woofer drive amplifier (IC1305). 

Sharp Electronics (UK) Limited - March 2003 

DA100 (50Hz) Chassis – Article for Television Magazine 

As with all current Sharp television chassis, the microprocessor (CPU) is responsible for the control of 
the set, communicating with all other areas of the chassis via various data buses. Similar to other 
chassis the CPU does not operate during standby.  As there needs to be some form of control on the 
primary side of the power supply, a slave processor is used.  This slave processor has a volatile 
memory, therefore each time power is applied to the television the switch mode powers supply has to 
start, enabling the slave processor program to be downloaded from the OTP before switching to 
standby. 

There are several types of communication lines that provide information to the CPU, and are used to 
control the various devices connected to it.  These are as follows.   

This provides communication between the CPU and the ROM (OTP, MTP or EPROM). This device 
contains the software (operating system) 

There are two I2C buses, I2C(2) is used to communicate with the NVM’s (EPROM’s), these devices 
contain data relating to all adjustments, whether it is an end user adjustment, service adjustment or 
an automatic setting performed by the CPU.  I2C(1) provides serial data communications between the 
CPU and Tuner, Video Processor, Multiple Sound Processor and the Dolby Processor (if fitted). 

This bus line provides data communication between CPU and the Megatext processor. 

Sharp Electronics (UK) Limited - March 2003 

DA100 (50Hz) Chassis – Article for Television Magazine 

There are two data lines that communicate with the slave processor located on the primary side of the 
power supply.  As this has to be isolated, communication is via two opto-couplers.  IC703 is used to 
send information to IC702 and opto-coupler IC704 is used for the return path.  

Main system reset.  This will operate each time the main switch mode powers supply starts. Reset is a 
state change from low to high generated by IC1005. 

IC801 reset (low). If IC801 is not reset then the line oscillator will not function. Reset out (1) will only 
occur after reset in. 

Resets all other areas of this television, this will only occur after reset out (1). Note that the reset 
for the teletext IC is inverted. 

It can be seen from the diagram below that all of the reset signals are a change in state, either from 
low to high or high to low. The order of events is as shown, supply, reset in, reset out (1), reset out (2). 
The horizontal oscillator will not start until reset out (1) has occurred.  Even though IC801 generates 
the horizontal drive signal, it will not be present until the mute has been released (HOUT=0V) 
 

Sharp Electronics (UK) Limited - March 2003 

DA100 (50Hz) Chassis – Article for Television Magazine 

The outputs from all of the audio output stages are fed to the base of Q303 and Q304. C377 and 
R361 form an averaging circuit.  As the output voltage fed to the speakers should have an average DC 
of 0V over a period of time, the DC voltage at the base of these transistors should be zero. If this 
base voltage were to increase in a positive direction Q303 will turn on, removing the bias from IC1001 
pin 100, and the television will switch to standby. The same is true if the base voltage increases 
negatively, this time Q304 will turn on, turning on Q302 causing IC1001 pin 100 to fall and the 
television will again switch two standby. 

If the beam current increases, D622 will conduct due to the ABL sense pin of T601 (earth return of 
the EHT over-winding) going more negative, Q606 will turn on.  This will remove the bias from IC1001 
pin 100 and the television will switch to standby 

During the boot sequence the horizontal drive is muted by the HOUT signal from the microprocessor 
(IC1001 pin 57).  Its function is to remove the horizontal drive by turning on Q607, thus placing a 
short between the horizontal drive signal and ground, at the same time this HOUT pulse will cause the 
audio mute circuits to activate, preventing any noise from the speakers during start up and shut down.  
HOUT will also occur when the microprocessor cannot communicate with the other devices connected 
to the I2C buses 

Sharp Electronics (UK) Limited - March 2003