Shut Down Circuit - Hitachi 51SWX20B Training

DP-2X LOW VOLTAGE POWER SHUT DOWN EXPLANATION
current condition caused by monitoring the current through the internal Switch MOS FET, the voltage will
rise and pin 5 has an internal Over Voltage detection op-amp. If this voltage rises enough to trigger this op-
amp, the IC will stop producing a drive signal.
5. (ABS) Pin 4 also has C915 monitoring spike current in case the CRTs "Snap" indicating a quick discharge
of High Voltage.
6. (BD) Pin 7 Monitors the Run Voltage generated by pin 18 of T901 for excessive voltage.
COLD GROUND SIDE SHUT DOWN SENSING CIRCUITS. (AC must be removed to recover).
(See DP-27 Signal Power Supply (Low Voltage) Shut-Down Circuit Diagram for details)
Looking at Pin 2 of I905 the shut down events are triggered by two routes.
D963, D962:
The cathode of D963 is connected through R982 to pin 10 of PPS3. This in turn is connected to R298 which is
connected directly to the 3.3V power supply produced by IP81 on the Signal PWB. If something were to load
this line down, D963 would forward bias and supply a current path for pin 2 of I905. This in turn would produce
a Shut Down event. See Power Supply Shutdown Photo Coupler I905 Explanation on the previous page.
Q910:
This transistor's base is connected to Q911 through D955. Q911 emitter is connected to Q912. This transistor is
the Shut down enable circuit.
DP-27 SHUT DOWN CIRCUIT:
There are a total of 3 individual Shutdown inputs to the photo coupler I905.
There are a total of 3 individual Shutdown inputs to the Relay Inhibit transistor Q903 from the power supply.
There are a total of 4 individual Shutdown inputs to the Relay Inhibit transistor Q903 from the Deflection Cir-
cuit. For a total of 10 individual Shutdown inputs that will kill the Lo Voltage Power Supply. (Note: The Hi Volt-
age Power Supply Shutdown will be discussed later.)
All of the Cold Ground side Shutdown detection circuits can be categorized by the two previously described cir-
cuits
In the following explanation, the Shutdown circuits will be grouped. This will assist the Service Technician with
trouble shooting the Chassis, by understanding these circuits and having the associated circuit routs, the techni-
cian can then "Divide and Conquer".
Voltage Loss Detection through I905 Photo coupler
•
Shorted STBY +3.3V generated by IP81 and monitored by (R298) on Signal PWB through PPS3 pin 10
to (D963) on Low Voltage Power Supply PWB. Labeled PROT-SBY on the Schematic.
•
Shorted SW+2.2V (IP52 pin 5) on Signal PWB monitored by RP53 through PPS3 pin 11 to to (D961)
on Low Voltage Power Supply PWB. Labeled PROT-SW on the Schematic.
•
Shorted SW+3.3V (IP52 pin 2) on Signal PWB monitored by DP53, RP53 through PPS3 pin 11 to to
(D961) on Low Voltage Power Supply PWB. Labeled PROT-SW on the Schematic.
•
Shorted SW+5V (IP53 pin 2) on Signal PWB monitored by DP54, RP53 through PPS3 pin 11 to to
(D961) on Low Voltage Power Supply PWB. Labeled PROT-SW on the Schematic.
Q903 Relay Inhibit Activation.
From the Power Supply.
SW +115V Voltage Too High Detection
•
Monitored by (D927) See additional Shut Down Circuit Diagram for details.
SW +115V Excessive Current Detection
•
Monitored by (Q905) See additional Shut Down Circuit Diagram for details
(Continued on page 12)
PAGE 01-11