Hitachi 46W500 Training page 17

DP-3X POWER SUPPLY SHUT DOWN EXPLANATION
On the Power PWB
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SW –7V Voltage Loss Detection Monitored by D949 and routed through D950. In this circuit, if the SW –7V is
lost, the positive +6.3V will forward bias D949 and it will fire causing shut down.
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SW –28V Voltage Loss Detection Monitored by D952 and routed through D953. In this circuit, if the SW –28V is
lost, the positive +28V will forward bias D952 and it will fire causing shut down.
In the Deflection Circuit
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–5V Voltage Loss Detection Monitored by DK90. In this circuit, if the –5V is lost, the positive +5V will forward
bias DK90. Any abnormality seen in the deflection circuit will generate a high that will be routed through the PPD4
connector pin 6 to D951. (See DP-3X Deflection Protect Shut-Down Circuit Diagram for details)
Voltage Too High Detection All voltage too high detections circuits are active (Hi) and routed to the base of Q904, Common
Action Circuit. (See DP-3X Power Supply Shut-Down Circuit Diagram for details)
On the Power PWB.
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SW +115V Voltage Too High Detection Monitored by D931 and routed through D930.
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Audio Ground If the Audio Output IC IAA1 has an internal short, the Audio ground will go positive. This is Moni-
tored by D960 and routed through D961.
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SW +10V Voltage Too High Detection Monitored by D957 and routed through D958.
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SW +5.5V Voltage Too High Detection Monitored by D947 and routed through D948.
From, the Deflection circuit output called Protect_Def.
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DH14 High Voltage Too High Sensing Circuit. This circuit monitors the High Voltage line generated by rectify-
ing the pulse from the flyback TH01 pin 5. If the voltage at the cathode of DH15 goes too high, this zener will fire.
This high will be routed to pin 6 of PPD4 to Protect_Def. Any abnormality seen in the deflection circuit will gener-
ate a high that will be routed through the PPD4 connector pin 6 to D951. (See DP-3X Deflection Protect Shut-Down
Circuit Diagram for details)
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At the same time, the zener diode DH14 will fire and this high will be routed to pin 7 of IH01. This is the
Horizontal Drive for High Voltage and this IC will shut off, turning off High Voltage drive pulses.
Excessive Current Detection (See DP-3X Power Supply Shut-Down Circuit Diagram for details)
On the Power PWB.
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SW +115V Excessive Current Detection Monitored by Q905 and D928 and routed through D930. If the Deflec-
tion/High Voltage Circuit draws too much current, R927 will develop a larger voltage drop. This will cause the base
voltage of Q905 to fall turning on this transistor. When this happens, it's collector will go high. This high will be
routed to D928 causing it to fire. This high will be routed through D930 and to the base of Q904 shutting off the
relay.
In the Deflection Circuit on the Power/Deflection PWB.
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Q604 Vertical Circuit Excessive Current Sensing Circuit. This circuit monitors the +28V line going to I601 Ver-
tical Output IC. If the IC draws too much current, R629 will develop a larger voltage drop. This will cause the base
voltage of Q604 to fall turning on this transistor. When this happens, it's collector will go high. This high will be
routed through D608 and to pin 6 of PPD4 to Protect_Def. Any abnormality seen in the deflection circuit will gen-
erate a high that will be routed through the PPD4 connector pin 6 to D951. (See DP-3X Deflection Protect Shut-
Down Circuit Diagram for details)
On the CRT PWB PROT_CPT. (See PROT_CPT & PROT_SW Shut Down Circuit Diagram).
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On the RED CRT PWB +220V Excessive Current Detection Monitored by RE35. If the 220V draws too much
current, the base voltage of QE08 will fall turning it on. The collector will go high. This high will go through
ERG1 pin 7, PSC pin 3, PPS4 pin 6 to D959.
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On the BLUE CRT PWB VM+220V Excessive Current Detection Monitored by REF1. If the VM220V draws
too much current, the base voltage of QEA8 will fall turning it on. The collector will go high. This high will go
through EGB1 pin 8, PSC pin 2, to the base of Q554 on the Signal PWB. This high turns on Q554B and it's col-
lector goes low. This low is routed to the PPS4 pin 5 to the cathode of D944 causing D945 to fire and pull the
base of Q906 low turning it on causing shut down.
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