SECTION K
INTERFACE BOARD (A24)
K.1. Principles of Operation
The Interface Board provides the Audio
Input, Failsafe, and remote control connec-
tions. Additionally, the Interface board is a
central connection point for many of the
connections between the Controller, PDM
Generator, RF Oscillator, Output Monitor,
PDM Amps, and PA boards.
U1 and Q3 are the contactor driver com-
ponents. U1 accepts a DC level input from
the Controller, and drives triac Q3. Q3 then
passes 24 VACcurrent to the start contactor.
K1, Q1, and Q2 determine if the transmit-
ter is to switch to the optional standby RF
Oscillator. In a normal condition, transistor
Q2 is biased ON by an output sample from
the Oscillator board. Q1 is then held OFF
by Q2.
If the RF Oscillator fails to produce RF
when it is supposed to be ON, Q2 shuts off
andallowsQ1toenergizeK1.Theenergiz-
ing of K1 puts the optional standby RF
Oscillator into operation.
Also included on the Interface board are
the remote status transistor packs U2, U3,
and U4. These provide open collector out-
puts which are able to drive TTL status
inputs of many remote control systems, or
a small DC relay or other indicating device.
K.2. Replacement/Alignment
Therearenoadjustmentsto bemadetothe
Interface board. However, the board must
either have provisions forthe standby oscil-
lator installed, or jumpers installed if this
option is not used.
K.3. Troubleshooting
K.3.1. Symptom: Green Power Level
Status LED’s Light On Control-
ler, But The Contactors Do Not
Energize
K.3.1.1. Open Interlock
If you have determined that this is not
caused by an open interlock, failsafe, or
phase monitor relay (A19K3), then the
problem may be on the Interface board.
K.3.1.2. 24 VAC Missing
Make sure that 24VAC is getting to fuse
F1. If it is not, there is a problem in the
wiring from the low voltage transformer.
K.3.1.3. ON Command Missing
ChecktoseeifyouaregettingaDC
control signal to the input side of optical
isolator, U1. A convenient check point is
R18.Ifit isnotpresent,theControllerboard
may not be providing the ON signal.
K.3.1.4. Bad Triac or Optical Isolator
Checktoseeifyouaregettingvoltageat
TB1-16. If AC voltageis presentat the fuse,
but not at TB1-16, then the problem resides
on the Interface board.
Replace U1 and/or U2 if the above tests
do not conclude that the problem is else-
where.
Rev.AE: 03-05-2002 888-2314-001 K-1
WARNING: Disconnect primary power prior to servicing.
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