switch), the corresponding terminal should be LOW, because the
transistor on the External Interface provides a current sink to
ground. When there is no status indication, the terminal should
be HIGH (close to the external supply voltage). Further trou-
bleshooting depends on remote control unit or remote indicator
circuits used.
N.4.5
Symptom: One Or More Remote Status Indi-
cations Remain “ON”; Transmitter Status In-
dication is Off (Green)
N.4.5.1
Possible Causes: Problem in Transmitter Fault and
Overload Logic
Use a voltmeter or logic probe to check the logic level to the
status interface circuit on the External Interface. When the trans-
mitter “Status” indication is not ON, the input at J6 should be
logic LOW. If the input is logic HIGH even when the transmitter
status LED is green or the pushbutton switch is not illuminated,
check transmitter fault and overload logic. Most fault and over-
load logic is described in SECTION P, Controller and SECTION
Q, LED Board.
N.4.5.2
Possible Cause: Shorted Transistor
The status interface transistors are in DIP integrated circuit
packages; pin-outs are shown on the External Interface sche-
matic diagram.
Check for a transistor emitter-collector short by removing primary
power from the transmitter, then disconnecting the external lead at
TB1 or TB2. Use an ohmmeter to check for a short to the transmitter
ground. A “good” transistor should read “open.”
N.4.6
Symptom: No Monitor Outputs (Analog Sig-
nal Outputs)
N.4.6.1
Possible Cause: No +15 VDC, Or -15 VDC, On Ex-
ternal Interface
Each analog voltage to the monitor output terminals is buffered
by a voltage follower. On-board zener diode regulators CR7 and
CR8 p15 VDC and -15 VDC to operate the voltage
followers. Failure of the zener diodes would result in no output
from the op-amp. Failure of one zener diode would result in
incorrect output or no output.
LOCATION
COMPONENT
FUNCTION/DESCRIPTION
B1
TB3
Terminal board, for audio input connections.
A2
J7
Used only in combined transmitter installations. (RF to combiner).
A3
J8
Used only in combined transmitter installations. (RF from combiner).
Table N-1. External Interface Board A28,
Controls and Indicators
Section N - External Interface (A28)
12-12-94
888-2297-002
N-5
WARNING: Disconnect primary power prior to servicing.
