Technical Manual
FT420
– Iss 2.4
48
Specifications
Function
Rating
Voltage input range
20
– 32Vdc
Fuse
15A (automotive blade fuse)
Low voltage shutdown
19V (approx.)
Audio input impedance
10kΩ
Output load
1Ω
Current draw
– quiescent (standby on)
40mA
Current draw
– quiescent (standby off)
140mA
Current draw
– full load
10A
Table 31 Connection of the Audio Amplifier 60W, 120W and 250W
Designator
Type
No.
Label
Pin
Description
CON1
Screw terminal
1
24Vdc
+
Power input. 19V - 32V, 3.1A (60W), 5.5A (120W), 11A
(250W)
2
-
CON2
Screw terminal
1
AUDIO IN
+
Audio input from the main control board. <=1V
RMS
. Input
impedance: 10K.
2
-
3
STDBY
Audio amplifier enable/disable input, logic 5V, <= 5mA. It is
to minimize the unit power consumption.
The amplifier output will be disabled when the input is high.
CON3
Screw terminal
1
AUDIO
OUTPUT
+
Audio output to the transformer secondary side on the Main
Control Board. 16V
RMS
to the associated different
transformer.
2
-
Note:
If Brooks OWS standby feature is not used then the higher current must be used in quiescent
power calculations.
3.9.4 OWS volume adjustment
All volume adjustments are made on the Audio Amplifier Module via the trimpot VR1 only. This
volume adjustment is given a reference designator, VR1 and named
“VOLUME” on all amplifier
boards. This trimpot, VR1, is located in both Figure 23 and Figure 25 do not use VR2 for adjusting the
volume at any time. VR2 is only used for factory calibration purposes.
The following procedures describe how to adjust the volume.
a) Manually turn on the evacuation tone.
b) Adjust the trimpot clockwise a little at a time to increase the volume on the audio amplifier.
c) Then test or measure if the required audio level is met.
d) Repeat b) to c) as necessary.
Table 32 OWS Audio Volume Adjustment
Designator
Description
Function
Factory Default
VR1
Audio volume control
Adjust the Audio input stage, fine tune.
Adjusted to the middle point.
VR2
Factory Calibrated
Reference voltage tuning for comparator.
(Do not adjust)
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