6-22 888-2408-002
WARNING: Disconnect primary power prior to servicing.
Troubleshooting
Table 4-1 on page 4-60 is intended to ease this confusion. For instance, in the
process of troubleshooting a PA problem it is found that amplifier B2 has no gate
control voltage. Tracking this back to its source can be tricky. Table 4-1 gives you
the necessary information to skip steps or at least verify your path.
According to Table 4-1, amplifier B2 is controlled by PAC#2. Following this across
the table, the PAC#2 output labeled PA6_GATE, on the PA Controller schematic, is
the control line for B2. Following this on across, this signal would also pass through
the Divider schematic as PA6 and connect to the combiner connector J6. The last 2
columns give the Isolation Switch # and the Isolation Resistor # associated with the
PA in question. In this case K6 and RT6 are used with amplifier B2. The Isolation
switches and resistors are located on the Isolation Board attached to each Z-Plane.
Also be aware that there could also be a problem on the RFI Filter boards which are
in series with all of the lines between the controllers and the PA components.
6.11 PA Controller Faults
The following paragraphs give a detailed description of all faults associated with the
PA Controller Boards. This mostly deals with the PAs and Isolation resistors. A
quick reference of these faults is given in Table 6-4 on page 6-37.
6.11.1 General PA Troubleshooting
As a general rule, the first step in troubleshooting any PA (or IPA) problem is to
swap the PA or the entire module with another in the transmitter. If the problem
moves with the PA, you have verified that it is the PA and not the slot to which it is
connected. If the problem appears to stay with the particular slot, then more
advanced troubleshooting of the Z-Plane or cabling back to the controller should be
explored. This is where Table 4-1 can save alot of time.
6.11.2 A or B#_OC, PA Over-Current Fault
The PA Current overload threshold for each PA is nominally 14.5 amps, provided
there are no failed PAs. If an individual PA exceeds this current, the PA will be
muted and the Combiner isolation switch will disconnect the associated isolation
resistor from the combiner and apply a ground to the PA output. This optimizes the
combiner for the other PAs until a TX_RESTART is initiated by pressing one of the
ON buttons. This will un-mute the faulty PA. If the current is still too high, the PA
will be switched out again.
However, it should be noted that the Z5 control system is adaptive. With the failure
of one PA, the other 3 PAs in that foursome will have a reduced PA current foldback
level due to the increased combiner mismatch. If a second PA fails, it depends on
where it is located in relation to the first one as to the action the controller will take
when reducing the current foldback limit on the PAs. Basically, this means that with
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