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DA100 (50Hz) Chassis – Article for Television Magazine
Faults in the Dolby Pro-Logic Circuit
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.
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.
Figure 49: Dolby Pro-Logic
PWB Connector
PWB Connector
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).
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).
Page 49 of 80
Sharp Electronics (UK) Limited - March 2003
Revision 2
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