5.3
Module Replacement/Alignment
DX-25U modules can be grouped in three categories when
replacement is required:
•
Modules which can be replaced with no adjustments.
•
Modules which require preset switch settings or jumper
plug positions
•
Modules which require adjustments.
5.4
Modules Which Can Be Replaced
With No Adjustments
The following modules may be replaced, or components on them
can be replaced, without making any adjustments, measure-
ments, or preset switch or jumper plug settings:
•
Buffer Amplifier (A39)
•
Predriver (A10)
•
PA Modules (RF33 through RF96)
•
External Interface (A28)
•
RF Multimeter (A23)
•
Fuse Boards (A24/A25)
•
Output Sample (A26)
•
Drive Splitter (A15)
•
Power Distribution (A39)
5.4.1
Buffer Amplifier (A16)
The Buffer Amplifier is broad-band, with no frequency deter-
mined components. If the Buffer Amp is replaced and a drive
fault is still indicated on the ColorStat™ panel, check the drive
level to the Predriver Module using the procedure outlined under
Frequency Change Procedure in this section.
5.4.2
Predriver
The Predriver Module is one of 79 identical RF amplifiers used
in the Driver and Power Amplifier stages, and therefore can be
interchanged if required. No adjustments are necessary if the
Predriver is replaced. Turn the transmitter ON and measure both
the Predriver voltage and current on the RF MULTIMETER to
verify that they are near the measurements indicated on the
Factory Test Data sheet.
NOTE
Adjustment of Predriver tuning control L1 is NOT required when
replacing the module. Changing the Predriver tuning can affect
the setting of the Oscillator sync used for VSWR protection.
If the Predriver is replaced and a Predriver Fault is still indicated
on the ColorStat™ panel, it is advisable to check the output to
the Driver stage using the procedure outlined under the Fre-
quency Change Procedure in this section.
5.4.3
PA Modules
The RF amplifiers used in the Power Amplifier stage are com-
pletely interchangeable as required. This can be done quickly by
depressing the OFF button, and opening the interlocked RF Amp
Compartment door inside the Center or Left Control Compart-
ment. Remove the defective RF amplifier by pulling it out and
then insert the replacement RF amplifier. The inner door can then
be closed and the transmitter returned to operation.
If the low voltage is left on when an RF amplifier is removed, the
ColorStat™ panel Cable Interlock LED will illuminate. Depress
the reset button to clear the Interlock indication. If the transmitter
will not turn on and the Cable Interlock LED remains red, check
to make sure the replacement RF amplifier is fully inserted. A
definite resistance should be felt when an RF amplifier is re-
moved or inserted in its slot.
For optimum performance the drive level to the PA Modules must
be correct. It is possible to get an idea if a replacement PA Module
is operating efficiently by operating the transmitter at full power
with normal modulation for 5 minutes. Shut the transmitter
down, turn off the Low Voltage at CB1 and CB2 and quickly open
the interlocked inner door. Compare the temperature of the
heat-sink on the replacement PA Module with other PA Modules
in the same area. If the PA Module is hotter than the others, drive
level and phasing should be checked. For Drive Level and
Phasing measurement procedures see “Measuring RF Drive
Level” and “Measuring RF Drive Phasing” paragraphs in the
Troubleshooting section.
5.4.3.1
Handling MOSFET’S
Due to the fragile nature of the gate of a MOSFET, special care
in their handling is required. The gate junction may be destroyed
by static electricity if it is allowed to discharge through the
MOSFET.
NOTE
MOSFET transistors which are in circuit are immune to this
damage.
The MOSFET transistors are shipped in anti-static packaging.
The transistors should remain in this packaging until they are to
be used or tested.
5.4.3.2
Testing MOSFET’s
The MOSFET’s will have to be removed from the circuit in order
to perform the following test.
Observe the precautions in the paragraph entitled “Handling
MOSFET’S” in this section.
Figure 5-1. Blower Motor Strapping
Section V - Maintenance
Rev. Z1: 06-02-00 Additional info to ECN 46105
888-2297-002
5-3
WARNING: Disconnect primary power prior to servicing.
