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DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 18 of 80
Degauss Circuit
This circuit is configured to ensure that the degauss circuit will not operate unless the switch mode power supply
is running and pin 14 of IC702 is low. A positive bias is applied to the emitter of Q714 from T701 pin 15
(rectified by D727 and limited by R762, R768 and D728) via the optical diac; IC708. Since Q714 is a pnp device,
once the base is taken low compared to the emitter, Q714 will turn on allowing current to flow through IC708
(LED section of this device), turning on the triac T702, allowing current to flow through the degauss coils.
is running and pin 14 of IC702 is low. A positive bias is applied to the emitter of Q714 from T701 pin 15
(rectified by D727 and limited by R762, R768 and D728) via the optical diac; IC708. Since Q714 is a pnp device,
once the base is taken low compared to the emitter, Q714 will turn on allowing current to flow through IC708
(LED section of this device), turning on the triac T702, allowing current to flow through the degauss coils.
Figure 8: Degauss Circuit
Current will continue to flow through the degauss coils until either the PTC (POR701) has increased in resistance
sufficiently to significantly reduce the current flow, or IC702 pin 14 goes high, turning of Q714, preventing
current flow through IC708, turning the triac T702 off. Since the default condition for IC702 pin 14 is low, it
can be seen that the degauss circuit should now operate each time the television is turned on from the main
on/off switch or switched from standby to normal operation. This is the case if the main processor has set up
communication with the slave processor or not.
sufficiently to significantly reduce the current flow, or IC702 pin 14 goes high, turning of Q714, preventing
current flow through IC708, turning the triac T702 off. Since the default condition for IC702 pin 14 is low, it
can be seen that the degauss circuit should now operate each time the television is turned on from the main
on/off switch or switched from standby to normal operation. This is the case if the main processor has set up
communication with the slave processor or not.
Sharp Electronics (UK) Limited - May 2003
Revision 3
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