4-36
888-2586-001
9/15/06
WARNING: Disconnect primary power prior to servicing.
Platinum Z16HD+
Section 4 Overall System Theory
The DRIVE_1 signal is used to activate the 48Vdc tap on T1 and T2 secondaries. This
tap is designated TAP 1 in the Diagnostics Display. When active (HIGH) it causes the
output of U2-17 to go low. This turns on Q1 which applies 20VB-SS, now called
DRIVE_1, to R16.
NOTE:
The 20VB-SS (SS = Soft Start) will only be present if the DISCHARGE signal at
J4-6 is inactive. See PA Power Supply Discharge later in this section for more
information.
The 20VB-SS forward biases diodes CR3, and CR4. This turns on the associated SCRs,
CR4 and CR8 on each power supply. Each of the SCR anodes are tied to ground with
the cathode connected through a 100 amp fuse to a tap on one of the transformer
secondaries. Note that all 4 power supplies will have selected the same relative (lowest
voltage) taps on each of the transformer secondaries.
4.6.2.2.2 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. Refer to the Rectifier
Board schematic for the following. 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, provided the Discharge signal is not active.
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.
4.6.2.2.3 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 Q8 to pull high through
R54, shutting Q8 off. This removes the 20VB-SS used to activate the transformer
taps. This prevents the PA Supply (and Soft Start) from being activated while the
DISCHARGE signal is active.
Summary of Contents for Platinum Z16HD+
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