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power from the amplifier. Dead level hysteresis
is provided by R724. R731 and D711 provide
un-interrupted battery power to the system RAM
so that stored instrument settings are retained
when the power is switched off.
POWER REGULATORS
The +5 V and +10 V supplies are produced with
three-terminal regulators U801 and U802,
respectively. The -10 V supply is constructed of
op-amp U803 and Q801, a N-channel MOSFET,
as the pass element. The +10 V supply serves as
the reference for the -10 V supply through
divider R809 and R810.
The power output banana jacks on the rear
panel(J801 and J803) are connected to the pre-
regulated voltages after the power switch and
before the regulators. This output can provide
up to 200 mA of power for use as an external
bias source, etc. Under some conditions, these
jacks may be used to supply the unit with
external DC power.
U506C and U506D generate the TTL level input
to the processor to indicate when the unit is
operating on the AC line.
Capacitors C801 through C811 are logic supply
bypass capacitors distributed throughout the
printed circuit board.
REAR PANEL INTERFACES
Three optically isolated rear panel interfaces are
provided on the SR570. The blanking input
accepts a TTL-level signal and opens the
amplifier signal path before the front end
differential amplifier for as long as the input is
held high. The toggling input also accepts a
TTL level signal and toggles the invert status of
the I to V amplifier output signal before the
front end differential amplifier for as long as the
input is held high. The response time of both
the blanking and toggling inputs is typically 5 µs
after the rising edge (turn-on) and 10 µs after the
falling edge (turn-off).
The RS-232 interface allows calibration and
control of the instrument at 9600 baud. Data in
and out on the connector are tied together,
echoing data back to the sender. Hardware
handshaking lines CTS, DSR, and CD are tied to
DTR. See the Remote Programming section for
more info.
BATTERIES AND P.E.M.
The batteries used in the SR570 are of sealed lead-
acid construction. There are three 12 volt, 1.9 amp-
hour batteries, two of which serve as the positive
power supply, and one of which serves as the
negative power supply. Powering the SR570 alone,
battery life should be 10-15 hours. The batteries
should last for more than 1000 charge / discharge
cycles, provided the guidelines under the usage
section are followed. Two 3A "slo-blo" fuses on the
rear panel protect the battery supplies and amplifier
against excessive currents.
The power entry module (P.E.M.) contains the AC
line fuse, RFI filter, and voltage selection card. To
change the operating voltage of the unit, the voltage
selector printed circuit card must be pulled out and
reinserted into the P.E.M. with the desired operating
voltage visible.
FRONT PANEL
The front panel contains the pushbuttons, LED
indicators and serial shift registers. The front panel
pushbuttons are decoded in a 3 x 5 matrix fashion.
The front panel LEDs are controlled by shift
registers U1 through U7, which allow the 7 eight-bit
control bytes to be serially shifted-in one bit at a
time. The red overload LEDs are controlled directly
from the output of the overload comparator. The
LINE, LOW BATT, BLANK, and TOGGLE LEDs
are also controlled directly from their respective
main board circuits.
The FREQ COMP pot P1 is mounted on the front
panel printed circuit board and is used to control the
main amplifier feedback capacitance.
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