888-2406-002
4-27
WARNING: Disconnect primary power prior to servicing.
Overall System Theory
transformer secondaries. Note that both power supplies have selected the same
relative (lowest voltage) taps on each of the transformer secondaries.
4.5.2.2.2 PA Power Supply Soft-Start
Soft-Start is used to limit the surge current during transmitter turn on. The Soft Start
and PA Power Supply Discharge circuits are able to use the same resistor, R48 since
only one or the other will be active at any one time. A simplified diagram of the Soft
Start and PA Power Supply Discharge circuits in shown in Figure 4-12. The Soft-
Start control signal is active high and comes directly from the PA Controller Board,
via J4-8. A high SOFT START signal at J4-8 causes U2-12 to go low. This turns on
FET switch Q5 which then applies the 20VB-SS through R18 to CR28 and CR29.
This in turn activates SCRs Q10 and Q11. The SCR outputs are labeled SS_A and
SS_B, and are connected to the 48V taps, H4 and H8, on the secondary of T1 and
T2. This allows the power supply to start charging through R48, a 5 ohm 100W
current limiting resistor. After about 5 seconds, the DRIVER 1 signal will activate
the normal 48V tap SCRs, CR4 and CR8, which will tie the taps directly to ground,
bypassing R48.
4.5.2.2.3 PA Power Supply Discharge
The PA Power Supply Discharge circuit uses R48 to bleed down the supply
whenever the transmitter is turned off. The DISCHARGE signal is active low and
comes from the PS Controller Board. When low, it causes the output of U2-14 to go
high. This does two things:
a.
First, it reverse biases CR31 which allows the gate of Q33 to pull high
through R54, thus shutting Q8 off. This removes the 20VB-SS used to acti-
vate the transformer taps. This prevents the PA Supply (and Soft Start) from
being activated while the DISCHARGE signal is active.
b.
Second, it allows the base of Q9 to pull high, shutting it off. R62 will then
pull the gates of Q6, Q7, Q12 and Q13 low, turning them on. Q6, Q7, Q12
and Q13 are switches which tie the 52Vdc to R48, and the supply is dis-
charged.
4.5.2.2.4 Voltage Samples
An AC voltage sample is taken from the 48V taps using 200k ohm resistors. One
from SS_A and one from SS_B. The samples are pulsating DC with a frequency of
120Hz and an amplitude whose average is equal to the DC power supply output.
They are sent to the PS Controller and used to control the tap switching based on the
amplitude of the pulses. The signals are also bandpass filtered at 60Hz to detect
blown SCR fuses.
To determine if a tap has failed (blown fuse), refer to the Diagnostics Display, see
Figure 4-14 on page 4-25.
Содержание Platinum Z2 CD
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Страница 20: ...1 6 888 2406 002 WARNING Disconnect primary power prior to servicing Introduction Specifications ...
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Страница 130: ...4 60 888 2406 002 WARNING Disconnect primary power prior to servicing Overall System Theory ...
Страница 156: ...5 26 888 2406 002 WARNING Disconnect primary power prior to servicing Maintenance and Alignment ...
Страница 194: ...6 38 888 2406 002 WARNING Disconnect primary power prior to servicing Troubleshooting ...
Страница 196: ...7 2 888 2406 002 WARNING Disconnect primary power prior to servicing Parts List ...
