Specifications
L.4.3.3.6 Supply Regulators
If the Encoder section of the Control front panel displays a supply
fault begin troubleshooting by:
a. Observing if the indicators DS12, DS13 and DS14 are
illuminated on each Mod Encoder board with CB3 on the
Power Supply Display panel in the STANDBY position.
b. If all these indicators are illuminated, turn on the transmit-
ter and monitor DS9 on each board for a flash that would
indicate the board generating the supply fault.
c. If DS9 does not illuminate on any board suspect a Control-
ler or cabling problem.
d. If DS9 flashes on all boards suspect a fault with the
Unregulated supply. Refer to the transmitter troubleshoot-
ing section to troubleshoot the low voltage supply.
L.4.3.3.7 DS12 not illuminated
This indicates that the unregulated +22 Volts is not present on the
board. Check F1 and if not open, troubleshoot the Low Voltage
Supply.
L.4.3.3.8 DS13 not illuminated
This indicates that the +5VA supply has failed.
a. Check F5 for approximately +12VDC. If not present refer
to the transmitter troubleshooting section to troubleshoot
the Low Voltage supply.
b. If F5 checks okay, suspect C73, C72 or U46.
c. If U46 is replaced check for a short on the +5VA supply
by measuring the resistance from CR41 cathode to ground
before applying power to the circuit
L.4.3.3.9 DS14 not illuminated
This indicates that the +5VB supply has failed.
a. Check F6 for approximately +12VDC. If not present refer
to the transmitter troubleshooting section to troubleshoot
the Low Voltage supply.
b. If F6 checks okay, suspect C156, C155 or U43.
c. If U43 is replaced check for a short on the +5VB supply
by measuring the resistance from CR54 cathode to ground
before applying power to the circuit.
L.4.3.3.10 DS9 illuminated
This indicates a B+ or B- supply is not active. To discover which
is at fault check DS8 and DS10 for illumination when switch S6,
on this board, is depressed.
CAUTION
DO NOT HOLD S6 DEPRESSED FOR LONGER THAN 1 MINUTE AT
A TIME. THIS WILL PREVENT DAMAGE OR OVERHEATING OF
THE REGULATORS.
L.4.3.3.11 DS8 Not Illuminated
If DS8 does not illuminate when S6 is depressed:
a. Check F3 for an open or +12 VDC.
b. If F3 is open check CR49, C62, C64 and U42.
c. If F3 is not open, remove Jumper J13 and depress S6 again
while monitoring DS8. If DS8 does not illuminate when
S6 is depressed, suspect U42, Q4, C51 or C52. Verify that
DS8 will illuminate before installing J13 back in the board.
d. If DS8 Illuminates suspect a short on the B+ line. Then see
sheet 3 of the schematic for the IC and bypass capacitors
and also check the Air flow sensor and CR55.
e. If +12 Volts is not present on F3 refer to the transmitter
troubleshooting section for the Low Voltage Supply.
L.4.3.3.12 DS11 Not illuminated
If DS11 is not illuminated when S6 is depressed:
a. Remove J13 and depress S6 again.
b. If DS11 illuminates suspect a fault on the B- line. Refer to
the schematic to locate the components involved.
c. If DS11 does not illuminate measure the voltage on TP22.
It should be approximately -12VDC.
d. If this voltage is not present refer to the overall trou-
bleshooting section to troubleshoot the Low Voltage sup-
ply.
e. IF TP22 measures correctly check F4.
f. If F4 is open suspect CR50, C60, C61 and U45.
g. If F4 is not open carefully remove U44 from its socket and
depress S6 again.
h. If DS11 illuminates Replace U44.
i. If DS11 does not illuminate, suspect U47 or U45 and
associated components.
L.4.3.4 Supply Fault Sensing
If all supply indicators illuminate properly, suspect the fault
sensing circuit. To begin:
a. Check for a logic low on the cathode of CR57.
b. If the low is not present the board is not generating the
fault. Refer to the overall wiring diagram, Transmitter
interface schematic and the Controller section as needed
to trace the fault.
c. If CR57 is low, observe if DS9 is illuminated.
d. If DS9 is not on, check Q5, C54 and CR57.
e. If DS9 is not illuminated suspect U37 or U49 associated
components.
L.4.3.5 RF Amp Turn On
L.4.3.5.1 All Off In Column
If all of the RF amps that are controlled by an encoder board will
not turn on, then:
a. Observethat all supply indicators are illuminated when the
transmitter is turned on.
b. If not refer to the supply troubleshooting portion of this
section.
c. If the supply checks correctly, check TP3 for Data strobe
signals.
d. If not present, check U15 and cabling from the Transmitter
Interface board.
e. If the Data strobe is present check DS1 and/or TP4 for a
logic low.
L-12 888-2339-002
WARNING: Disconnect primary power prior to servicing.