Fluke PM6690, Service Manual, Page: 20 / 200

The terms in the following figure are used in all descriptions
in this manual.
The PM6690 can be equipped with a number of options and
accessories. Built-in timebase and prescaler options can be
identified by pressing
USER OPT
®
About on the front
panel.
The following built-in options exist or are planned:
– Option PM6690/6__ 3 GHz RF Prescaler Input
– Option PM6690/7__ 8 GHz RF Prescaler Input
– Option PM6690/_5_ Very High Stability OCXO
– Option PM6690/_6_ Ultra-High Stability OCXO
The location of these optional parts is illustrated in Fig. 3-2
and Fig 3-3.
Removing the Cover
WARNING: Do not perform any internal ser-
vice or adjustment of this instrument
unless you are qualifyed to do so.
WARNING: When you remove the cover you
will expose live parts and accessible ter-
minals which can cause death.
WARNING: Although the power switch is in
the OFF position, line voltage is present
inside the instrument. Use extreme cau-
tion.
WARNING: Capacitors inside the instrument
can hold their charge even if the instru-
ment has been separated from all voltage
sources.
– Make sure the power cord is disconnected from the
counter.
– Turn the counter upside down.
– Remove the two screws at the bottom and the two
screws in the rear feet.
– Remove the four decorative plugs (C) that cover the
four screw holes on the right and left side of the front
panel.
– Grip the front panel and gently push at the rear.
3-2 Disassembly, Removing the Cover
Front Bottom
Right
Rear Top
Left
Figure 3-1
Terms used in this manual.
Rear Panel Inputs
Basic Board
Power Supply
RF Inputs
3 GHz & 8 GHz
Input Amplifier
Optional
Oscillator
Fan
Figure 3-2
Interior layout including 3 GHz or 8 GHz
prescaler option.
RF Input 20 GHz
Figure 3-3
Interior layout with 20 GHz prescaler option.