Ericsson EDACS 19D902120G1, Maintenance Manual, Page: 3 / 14

Supply Voltage
The receiver is supplied by a regulated 10 volts from the
system board. However, the more critical circuits are supplied by
voltage regulators U5, U7 and U8 for stability and isolation.
Regulated 10 volts from the system board is used to supply
RF amplifier U1, IF amp U4, VCO transistor Q3, and RF buffer
Q4. Regulator U5 provides the 5-volt supply for audio IC, U6,
and 5-volt regulator U7 supplies counter U9, Phase detector U10,
and RF amps Q1 and Q2. The 8-volt regulator (U8) provides
power for RF amp U3 and audio buffer Q5.
AUDIO BOARD
Audio board 19D902181G1 consists of a preamplifier cir-
cuit, squelch detector, audio IC and audio PA circuit. The audio
board is connected to the system board through P904. The
discriminator output is connected through J601-3 on the audio
board. Power is supplied from a regulated 10 volts from the
system board. A Block Diagram Of the audio board is shown in
Figure 2.
Audio Preamplifier
Discriminator audio from J602-3 is coupled through Audio
Level Adjust R608 to the preamplifier circuit. The preamp con-
sists of Q601, Q602, Q605 and associated circuitry, and provides
26 dB of gain. The amplified output is connected to the squelch
and audio hybrid ICs through the arm of the VOL and SQ
controls on the exciter-receiver door assembly.
Receiver Audio
The audio circuitry consists of a three-stage, quad integrated
circuit (U602-A, U602-C and U602-D). The three stages provide
a standard EIA Channel Guard tone reject filter, a receiver
de-emphasis circuit, and the low level audio driver circuitry.
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Figure 2 - Block Diagram; Audio Board 19D902181G1
LBI-38163
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