Specifications

G.5.8 RF Drive Fuse Open Detector
RF Drive passed by F3 will conduct through CR19 and charge
C11 to about 20VDC. CR17 is therefore reversed biased and
P1-35 remains at +15VDC. If F3 opens, the charge on C11 will
be removed and 20K ohms of resistance will effectivelybeplaced
to ground through CR17 and R19. This will lower the voltage
going to the Mod Encoder and is used to trip a fault comparator
which lights the RF Amp Fuse LED on the Front Panel. The same
operation applies to circuitry connected to F4.
G.5.9
DC Supply Fuse Open Detector
If F1 opens due to shorted MOSFETs on section A, the voltage
at P1-35 (normally +15VDC) will be shunted to ground through
R31 and CR11. This will lower the voltage going to the Mod
Encoder and is used to trip a fault comparator which lights the
RF Amp Fuse LED on the Front Panel. The same operation
applies to circuitry connected to F2. If CR11 or CR12 short, R31
and CR25 will clamp the 230 VDC present at F1 or F2 down to
20 Volts on the fuse open detector line (P1-35), thereby protect-
ing the Mod Encoder.
NOTE: For more information on the Fuse Fault circuitry refer to
Section L, Modulation Encoders.
G.6 Maintenance
G.6.1 Handling MOSFETs
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 the static electricity is allowed to discharge
through the MOSFET. For example, walking across a carpet to
pick up a MOSFET that is not protected by antistatic packaging
could result in the destruction of the MOSFET. A static charge
could build up on a person as they walk across the carpet. This
Figure G-4. RF Amplifier Simplified Control Circuit
Figure G-5. Induced RF Current Path for Module
OFF Condition
888-2339-002 G-5
WARNING: Disconnect primary power prior to servicing.