A1 Connector Board Circuit Theory; High Voltage Power Supply Switch (A1Q3 And A1Q4); Power Distribution; Table 8-2. Dc Unbalanced Failures - HP 5501B Operating And Service Manual

Laser head

Table of Contents

8-73. A1 CONNECTOR BOARD CIRCUIT THEORY

8-74.

The A1 Connector Board interconnects the main laser cable, laser tube heater and power amp,

laser power supply, and the A3 Controller/Reference Board. The schematic diagram for A1 is

shown in Figure 8-23. Additional information covering heater power amp control circuitry can be

found in paragraph 8-119.

8-75.

Capacitors A1C1 through A1C4 serve to filter out noise on the ±15 Volt power supply lines.

Capacitors A1C6 and A1C7 and inductors A1L1 and A1L2 filter current spikes created by the

high voltage power supply and the switching power amplifier. Diodes A1CR1 and A1CR2 provide

reverse voltage protection. Switch A1S1 is a safety interlock which removes power from the laser

high voltage power supply when the HP5501B covers are removed. Switch A1S2 bypasses the

interlock so that the laser can be serviced. A1S1 and A1S2 are wired in such a way that the

interlock must be enabled before replacing the covers. A1F1 and A1F2 protect the system

against laser power supply failures. A1J4 is the connector for the laser tube heater and cathode.

A1DS3 and A1DS4, +15V POWER ON and -15V POWER ON LED's respectively, turn on when

the power cable is connected to POWER connector A1J5. A1DS7 (LASER ON LED) lights when

the high voltage supply is powered on, and A1DS8 (READY LED) lights when the HP5501B is

ready for use. A1R12 is used to adjust laser current as per the adjustment procedures in

8-76. High Voltage Power Supply Switch (A1Q3 and A1Q4)

8-77.

When optical mode begins, the laser beam should be on. This is accomplished by applying the -

WARMUP logic line through current limiting resistor A1R10 to the base of transistor A1Q4. A1Q4

saturates which, in turn causes A1Q3 to turn on and saturate. The high voltage power supply

senses ground through saturated A1Q3, thus turns on.

8-78.

If the HP5501B left and right covers are placed on the unit prior to resetting the TEST-NORM

switch (A1S2) to NORM; both SUPPLY UNBALANCE LED's will turn on. When power is applied,

A1 transistors Q1 and Q2 sample the heater switching voltage through ac voltage divider A1R23

and A1R24. A1C5 ensures that transistor bases of A1Q2 and A1Q2 remain at "virtual" dc ground

so that the unbalance circuits operate normally.

8-79. Power Distribution

8-80.

When +15 Vdc and -15 Vdc are applied to the laser head, the ±15V POWER ON light-emitting

diode indicator (on the A1 Connector Board) are forward biased and illuminate. The dc input

potentials also produce a virtual ground level at the junction of two 14.7K Ohm resistors. This

balanced condition results in an open circuit at transistors A1Q1 and A1Q2. An unbalanced

condition exists when either the positive or negative dc input deviates from 15 Volts by

approximately 1 Volt or more. This offset causes a corresponding forward biasing of A1Q1 or

A1Q2 thus placing the anode of LED DS5 or DS6 (±15V SUPPLY UNBALANCE) at "virtual"

ground potential. Table 8-2 lists the unbalanced DC voltage conditions and the resulting

unbalanced indications.

DC INPUT VOLTAGE UNBALANCED CONDITION

+15 Vdc

-15 Vdc

8-26

Table 8-2. DC Unbalanced Failures

High (more positive)

Low (less positive)

High (more negative)

Low (less negative)

UNBALANCED INDICATORS

+15V SUPPLY

-15V SUPPLY

UNBALANCE

OFF

HP5501B

Service

Section

OFF