24 Maintenance Manual
Page 2: SRC_A is then connected to K1, which is used to direct it to either
speaker A at J5-A pin T4, or toward the ER3(U2-A pin 8) and the
Headphone(U4-A pin 8). SRC_B is then connected to K2, which is used
to direct it to either speaker B at J5-B pin T2, or toward the ER3(U2-A
pin 2) and the Headphone(U4-A pin 2). U2-A is then used to direct the
A or B signal to the ER3 at J3 pin 1. U4-A is then used to direct the A or
B signal to the both channels of the headphone at J4 pins T3 and R2.
RETURNING CURRENT:
Page 2: The speaker return currents arrive at J5-A pin C6 and J5-B pin C1. They
are then connected to SRET_A and SRET_B respectively. The ER3
return current arrives at J3 pin 3 and is routed to the same channel that
the outgoing signal came from, (SRET_A or SRET_B), by U3-A. The
Headphone return current arrives at J4 pin C1 and is routed to the same
channel that the outgoing signal came from, (SRET_A or SRET_B), by
U5-A.
Page 1: SRET_A and SRET_B are then sent back to the Connectorboard via J2
pins 3 and 11.
4.4.2 Measurement Microphone Circuits Signal Flow
4.4.2.1 Chamberboard schematic (061-x178-0x)
Page 3: The coupler microphone signal arrives at J7 pin 1. U5-A, U10-A and as-
sociated components are the 24dB Prescaler. U5-B, U6-A and associated
components re-reference the microphone ground from chassis to the lo-
cal Analog Ground. U6-A also acts as the positive half of the differential
line driver which drives the MICAB+ line. U10-B, U6-B and associated
components are the negative half of the differential line driver which
drive the MICAB- line. Turning the negative driver on increases the
output of the differential receivers on the connectorboard by 6dB. So the
negative half of the differential driver is also the 6dB Prescaler. The PR-
ESCALE and 6DB_ATTTEN control signals come from U1-A on page 1.
J5 is used to connect the 30.1K -10V bias resistor to the mic input signal
if needed. The M1950 does not need this bias current. The older M1750
does need the bias current.
Page 1: The MICAB+ signal is sent out to both the MICA+ and the MICB+ lines
on J2 pins 1 and 2. The MICAB- signal is sent out both the MICA- and
the MICB- lines on J2 pins 8 and 9. These signals are then sent to the
Connectorboard. The PRESCALE and 6DB_ATTEN control signals origi-
nate on U1-A pins 54 and 13.
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