Harris Platinum Z16HD+, Предварительное руководство

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9/15/06 888-2586-001 4-33
WARNING: Disconnect primary power prior to servicing.
Section 4 Overall System Theory
Platinum Z16HD+
connections). Note that both the “A” and “B” side SCRs have selected the same relative
(lowest voltage) taps on each of the two transformer secondaries.
4.6.1.2.2 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. The Soft-Start control signal is active
high and comes directly from one of the PS Controller Boards, via J4-8. A high SOFT
START signal at J4-8 causes U2-12 to go low. This turns on FET switch Q32 which
then applies the 10VB-SS through R65 to CR28, CR29 and CR30. This in turn activates
SCRs Q34, Q35 and Q36. The three SCR outputs are labeled SS1-B, SS2-B and SS3-B
and are connected to the 48V taps on the transformer “B” secondaries of each
transformer. This allows the power supply to start charging through R48, a 5 ohm 100W
current limiting resistor. After about 3 seconds, the DRIVER 1 signal will activate the
normal 48V tap SCRs which will tie the taps directly to ground, bypassing R48.
4.6.1.2.3 PA Power Supply Discharge
The PA 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, shutting Q33 off. This removes the 10VB-SS used to activate the trans-
former 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 Q37 to pull high, shutting it off. R62 will then pull
the gates of Q29 and Q31 low turning them on. Q29 and Q31 are switches which
tie the 52Vdc to R48, and the supply is discharged.
4.6.1.2.4 Voltage Samples
Two AC voltage samples are taken from the 48V taps using 301K ohm resistors. One
from the “A” secondary at J4-14 and one from the “B” secondary at J4-13. The samples
are pulsating DC with a frequency of 360Hz 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 average (DC) amplitude of the pulses. The signals are
also bandpass filtered at 60Hz to detect blown SCR fuses and 120Hz to detect the loss
of one AC input phase.
To determine if a tap has failed (blown fuse), refer to the Diagnostics Display. For
example to check the status of the taps on Power Supply 1 (PS1), Press [STATUS, A, B,
C, D] This will show you the screen in Figure 4-14.