Hal Communications ST-6000, Instruction Manual

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5-7
the state of the received data (mark = on), regardless of the condition of the autostart or KOS cir-
cuits. This lamp also indicates the status of the pre-autostart data output.
Similarly, the SPACE lamp is used to indicate the status of the post-autostart data (space = on)
and will therefore be controlled by the autostart and KOS circuits.
The AUTO LED indicates the status of the autostart circuit and is on whenever the autostart
control line will allow passage of the received signal to the post-autostart data output. Notice that,
if the autostart is turned OFF with the front panel switch, this AUTO lamp will remain on.
The LOOP LED (see Figure 5.10) is driven directly from the Loop Sense circuit and therefore in-
dicates the status of the "Main" keyer transistor or Loop 1. This lamp is on for mark condition and
off for space condition.
The status of the KOS circuit is indicated by the KOS LED. This lamp is on whenever the KOS
circuit is in the transmit condition (see Figure 5.12).
The POWER lamp (Figure 5.13) senses the presence of BOTH the +12 and –12 Volt outputs of
the main power supply. Thus, a failure or either voltage will reduce the intensity of the lamp and a
total power failure will extinguish the lamp.
5.4 Power Supply (Figure 5.13)
The main Power supply rectifiers, filters and regulators are constructed on the control circuit
board. The power transformer, loop resistor, and fuses are mounted directly on the cabinet.
The +12 and –12 voltages required by the ST-6000 are derived from a full-wave bridge rectifier.
The +12 Volt supply is regulated with a type 7812 integrated circuit regulator, the –12 Volt by a
type 7912 IC. As noted previously, the POWER LED indicates presence of BOTH voltages.
The +175 Volt, 60 mA loop voltage is derived from a full-wave rectifier. The LOOP fuse and cur-
rent limiting resistor are mounted on the cabinet. The plus lead of the loop supply is routed to the
rear-panel connector board, through the fuse, the limiting resistor, to the Loop 3 connector (J7, pin
1). Pin 3 of the Loop 3 connector is then connected via the circuit board to pin 1 of the Loop 1 and
2 connector (J8), where it is called "Loop High (+)". Therefore, a jumper or TTY machine MUST be
connected between pins 1 and 3 of the Loop 3 connector to use either the "Main" (Loop 1) or
"Auxiliary" (Loop 2) keyer stages.
5.5 Oscilloscope (Figure 5.14)
The tuning oscilloscope section in the ST-6000 includes the 1" cathode-ray-tube, its front-panel
controls, vertical and horizontal deflection amplifiers high voltage power supply and a power trans-
former with high-voltage winding for the CRT. The high voltage supply is contained on one circuit
board that mounts directly to the tube shield. The supply is arranged to generate both +480 Volts
and –240 Volts. The deflection amplifiers and bias networks for the CRT are constructed on a sec-
ond circuit board, mounted on the other side of the tube shield. The two deflection amplifiers are
identical and have sufficient voltage gain to permit more than full screen deflection with the 2 Volt
p-p signals available from the discriminator filters. Gain controls are provided for both horizontal
and vertical amplifiers to permit user adjustment of the screen deflection, if desired. The gain con-
trol potentiometers are located on the board to the right of the CRT, looking back from the front
panel. The control closest to the front panel is for vertical gain and the other control is for horizon-
tal gain adjustment. A third potentiometer on this board is the ASTIG adjustment. This control can