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OPTIMOD
±5VDC for the analog circuits and +5VDC for the digital circuits. An unregulated volt-
age powers the LED backlight on the LCD display.
Component-Level Description:
L1 is a power line filter that filters out RFI. F1 is a 1/2-amp "Slo-Blo" fuse. T1 is
a dual-primary dual-secondary power transformer used to step down the input
voltage for the ±15VDC analog and +5VDC digital supply regulators. Each pri-
mary winding has a Metal-Oxide Varistor (V1, V2) connected in parallel to sup-
press high-voltage spikes across the AC line. Rear panel switch S1 configures the
primary windings either in parallel (for 115V ±15% line voltages) or series (for
230V ±15% line voltages).
T1 has three secondary windings for stepping down the AC line voltage. The
lower voltage winding feeds storage capacitors C15 and C19 through full-wave
bridged rectifier diodes CR13, CR14, CR15, CR17 and CR18. C15 filters the rec-
tified voltage for input to low-dropout linear voltage regulator IC5, which pro-
vides the +5VDC source used to power all of the digital circuits in the 6200. C19
filters the rectified voltage to power the LED backlight on the LCD display. Com-
ponents Q1, Q2, R3-R7, and CR20 form a pulsed current source to illuminate the
25x2 LED array (the backlight on the LCD display). The signal LEDPULSE, a
48kHz pulse at 1/8 duty cycle, feeds the base of high-current Darlington transistor
Q1. The feedback circuit consisting of Q2, CR20 and R3-R7 controls the magni-
tude of the signal LEDPULSE so as to limit Q1's current pulses to about 1.5A (1/8
duty cycle). These current pulses illuminate the 25 x 2 LED array via keyed
header J201, which attaches the LED array between the collector of Q1 and sup-
ply cap C19. The signal LEDPULSE is gated on for approximately one hour after
the 6200 has last been powered up or a front panel button has last been pressed;
otherwise, it is gated off. This drastically increases the lifetime of the LCD display
and saves power. The LED meter circuits are described in "User Control Interface
and LED Display Circuits."
The higher voltage pair of transformer secondary windings is configured in series
to form a single center-tapped winding. This winding is connected to rectifier di-
odes CR1-CR4 in a full-wave center tap configuration. C1 and C2 filter the recti-
fied voltage for input to the voltage regulators IC1 and IC2. These regulators pro-
vide the +15VDC and −15VDC sources used to power most of the analog circuits
in the 6200. They also serve as the respective inputs to the voltage regulators IC3
and IC4. IC3 provides the +5VDC analog supply for the converter chips, which
draw only a modest amount of current through power-dissipating resistors R8-
R15.
Test points and supply bypass capacitors are placed throughout the PC board. S2
is the ground lift switch used to connect or lift 6200 circuit ground from chassis
ground.
6-19
TECHNICAL DATA
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