Hitachi 46W500 Training page 16

DP-3X POWER SUPPLY SHUT DOWN EXPLANATION
COLD GROUND SIDE SHUT DOWN SENSING CIRCUITS. (AC must be removed to recover).
Looking at the base of Q904 the shut down events are triggered by the following.
SHUT DOWN CIRCUITS:
There are a total of 23 individual Shutdown inputs to the Relay Inhibit transistor Q904. Many of these are discrete circuits and
will be described later. However, there are some that are routed to the Power Supply from external circuits not shown on the
Power Supply Shut Down circuit diagram.
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There are a total of 3 individual Shutdown inputs from the Deflection PWB via Protect_Def routed through steer-
ing diode D951. (See Deflection Protect Power Supply Shut Down Circuit Diagram).
1. Vertical Output I601 Excessive Current Detection
2. -5V Loss Detection
3. Excessive High Voltage Detection
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There is 1 Shutdown input from the Protect_CPT circuit routed through steering diode D959. This input is from
QE08 on the Red CRT PWB. From the Red CRT PWB to the Green CRT PWB via ERG1 connector pin 7 called
VM Protect, Green CRT PWB to Signal PWB via PSC connector pin 3 called VM Protect, from Signal PWB to
Power PWB via PPS4 connector pin 6 called Protect_CPT. This signal would be high if the +220V draws exces-
sive current on the Red CRT PWB. (See PROT_CPT & PROT_SW Shut Down Circuit Diagram).
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There are 6 individual Shutdown input from the Protect_SW circuit monitored by D944.
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1 of these inputs is from QEA8 on th the Blue CRT PWB. From the Blue CRT PWB to the Green CRT PWB
via EGB1 connector pin 8 called Gain.Cont. From the Green CRT PWB to Signal PWB via PSC connector
pin 2 called Gain.Cont. From the PSC connector pin 2 to the base of Q554 which inverts this High to a Low.
From Q554 collector to the PPS4 connector pin 5 now called Protect_SW. From the Signal PWB to Power
PWB via PPS4 connector pin 5. This signal would be low if the +220V draws excessive current on the Blue
CRT PWB.
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5 of these inputs are monitoring for a shorted B+ line. These circuits are on the Signal PWB 2 of 3. They moni-
tor the following;
1. SW +2.2V from I404 pin 4.
2. SW +3.3V from I403 pin 3 monitored by D402.
3. SW +9V monitored by D404.
4. SW +9.3V monitored by D403.
5. SW +5V from I402 pin 3 monitored by D401.
(See PROT_CPT & PROT_SW Shut Down Circuit Diagram).
All of the Cold Ground side Shutdown detection circuits can be categorized by the previously described shut down circuits
which were discussed in the Generic Shut Down Circuits Explanation section.
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 technician can then "Divide
and Conquer".
Voltage Loss (or Short) Detection All short detections signals active (Lo). Routed to the base of Q906 which inverts the
signal to a (Hi) then through D933 to the base of Q904, Common Action Circuit.
On the Signal PWB 2 of 3
PROT-SW All routed through PPS4 pin 5 to D944 on Power PWB. Labeled PROT-SW on the Schematic. (See
Prot_CPT & Prot_SW Shut Down Circuit Diagram)
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Shorted SW+2.2V (I404 pin 4) monitored by R420
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Shorted SW+3.3V (I403 pin 3) monitored by D402
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Shorted SW+5V (I402 pin 3) monitored by D401
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Shorted SW+9V monitored by D404
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Shorted SW+9.3V monitored by D403
(Continued on page 9)
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