HP 2040D - Manual (Page 53)

Series 2040 Test System
Series 2040 Maintenance Manual V2.00 Module Repair and Replacement
52
INTERNAL AND PATCHBOARD POWER SUPPLY OVERVIEW
The Testhead Power Supply Controller monitors Testhead power supplies for
overvoltage with OVP crowbar IC’s. When an overvoltage is detected, the
OVP IC quickly short circuits the offending power supply. This produces an
undervoltage state on that power supply. This is, in turn, sensed by an opto-
isolated comparator to produce a digital fail signal. This digital signal is latched
in the control circuit and removes the AC line power from the Testhead
Internal and/or Patchboard Power Supplies. The state of all comparators is
indicated by the LEDs mounted on the top edge of the controller circuit card.
An illuminated LED in the power supply group indicates a normal condition.
The “PBON”, “RESET”, “PROX” and “EXTERNAL FAULT” LEDs, when all are
illuminated, indicate that power is applied to the patchboard. The
extinguishing of any LED shows the reason for the loss of power to the
Patchboard and/or the Testhead. A dedicated power supply on the controller
circuit card maintains its function without regard to the monitored supplies.
The result of the logical OR of any Testhead Internal Power Supply failure is
logically OR’d with any Patchboard Power Supply failure. The result of this is
provided as a current loop signal through an opto-isolator to the UUT Power
Supply Controller. Therefore, when a fault is detected in the Testhead Internal
Power Supply, all power supplies are shut down. If the fault originates in the
Patchboard Power Supply, the Testhead Internal Power Supply remains on.
The Testhead Power Supply Controller also responds to three external logic
signals. They are the Patchboard Open Sensor, CPU ON/OFF command and
Reset. A proximity detector, located near the Patchboard, senses the release of
the Patchboard and causes a shutdown of the Patchboard Power Supplies,
and indirectly the UUT Power Supplies. The CPU ON/OFF command (see the
functional call POWER) is a programmed command where a “0" causes the
Patchboard Power Supplies to shut down without a detected fault condition.
A ”1" enables the Patchboard Power supplies. The Patchboard Power is
removed when a Testhead reset is issued. (See the TCLEAR functional call in
the Programming Manual). When the Patchboard Power Supplies are shut
down, they are also disconnected from the Patchboard via relays.