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DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 20 of 80
Overriding the Power Supply Control
It is possible to ascertain if the power supply is working by removing the standby control voltage from the base
of Q702. If R792 is disconnected, the power supply should start if there are no other problems with it or the
supply lines. It is good practice to disconnect R623 when undertaking this exercise, as this will ensure that the
horizontal output stage does not become active. If R623 is not disconnected, and there is a fault in the
horizontal stage, the power supply may not start. When the power supply starts with R792 disconnected, it
should regulate correctly. Note that supplies can be disconnected, but the integrity of the feedback loop must
be maintained, failure to do so would result in very high HT and subsequent component faults.
of Q702. If R792 is disconnected, the power supply should start if there are no other problems with it or the
supply lines. It is good practice to disconnect R623 when undertaking this exercise, as this will ensure that the
horizontal output stage does not become active. If R623 is not disconnected, and there is a fault in the
horizontal stage, the power supply may not start. When the power supply starts with R792 disconnected, it
should regulate correctly. Note that supplies can be disconnected, but the integrity of the feedback loop must
be maintained, failure to do so would result in very high HT and subsequent component faults.
Figure 11: Location of R792
Figure 12: Location of R623
Sharp Electronics (UK) Limited - May 2003
Revision 3
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