HP 3000 SERIES II System Service Manual page 189

System Service
B-36. Over/Under Voltage Protection. The +5 and +12 volt outputs are sensed for overvoltage to
protect the TTL circuits on the Semiconductor Memory Control PCA and the memory chips on the
Semiconductor Memory Array PCA. An overvoltage condition causes the crowbar to fire and sets
the crowbar latch. Firing the crowbar pulls the +16.45 volt line to ground and opens fuse Fl. The
crowbar latch produces a regulator override signal which is sent to the TEMP SENSE input of the
HP 30310A Power Supply. The regulator override signal also causes the +20 volt line to drop to
approximately +0.2 volt. The +15 volt line from the HP 30310A Power Supply is maintained to
keep the crowbar latch energized. The HP 30311A Power Supply is then completely shut down
(fuse Fl opens and there is approximately 0 volts on the +20 volt line).
The +12, +5, and -5 volt outputs are sensed for undervoltage to disable the PSU (Power Supply Up)
power control lines at tum on (when all the output signals are above their undervoltage levels).
Enabling PSU to the HP 30310A Power Supply enables the start of the 0.6-second delay to the
system PON line.
B-37. Battery Test. Located on the rear panel of the power supply is a momentary toggle switch
labeled BATTERY TEST. This switch places the power supply in the battery discharge mode. When
the switch is depressed, the crowbar latch is set providing a REGULATOR OVERRIDE signal that
effectively forces the +20 volt line to approximately 0 volts. Fuse Fl is not opened and the power
supply operates from the battery pack as evidenced by the BATTERY STATUS indicator flashing
at a 2-Hertz rate and the CROWBAR/BATT TEST indicator turning on. The computer should be
halted before this simulated power fail verification is attempted. The power supply is returned to
normal operation by momentarily pressing the RESET switch which is located on the power supply
front panel.
B-38. CONTROLS AND INDICATORS
Controls and indicators mounted on the front panel of the HP 30311A Power Supply and on the
DC Control Panel are provided to monitor and control power supply status and operation. In
addition, test points on the power supply front panel are provided as an aid in troubleshooting. An
internal three-position slide-switch permits power supply operation with a battery or without a
battery, and in the calibrate position allows setting of the battery float voltage level.
Figure B-6 shows the locations of the controls and indicators on the power supply panels and on the
DC Control panel. Table B-4 lists the function of each control and indicator. The BATTERY
STATUS indicator is duplicated on the power supply, on the DC Control Panel, and on the top of
the cabinet door of the main bay. The power supply +5 indicator is also duplicated on the DC
Control Panel as the SYSTEM DC POWER indicator.
B-28
JAN 1977