
Model 8640B
TM 9-4935-601-14-7&P
5-18. Wrench
. A wrench is supplied with the generator.
One end fits the SMC connectors used on the
generator's RF cables, the other end fits another
common size SMC connector which may be used in
servicing the instrument.
5-19. FACTORY SELECTED COMPONENTS
5-20. Table 5-1 contains a list of factory selected
components by reference designation, basis of
selection, and schematic diagram location. Factory
selected components are designated by an asterisk (*)
on the schematic diagrams in Section VIII.
5-21. The following information supplements Table 5-1.
a.
A8A1R4 Selection
. If A8A1U5 has been
replaced and counter external sensitivity is not within
specification, select A8A1R4 as follows:
1. Set COUNTER MODE to EXT 0-10 or EXT 0-
550.
2. Measure dc voltage at A8A1U5 pins 1 and 14.
3. Select a value of resistance that will bring dc
voltage at pin 14 to within 10% of voltage at pin
1.
b. A10A2R6-8, R12-14, and R18-20 Selection.
If A26U2 (Service Sheet 12) has been replaced, check
second harmonic level (at RF output jack) on the
following bands: 128-256 MHz, 64-128 MHz, and 32-64
MHz. If second harmonic level is out of specification,
increase affected band's divider output attenuation until
second harmonic level is within specification. The
following table indicates correct values of resistance for
3 to 6 dB of attenuation (change attenuation in 1 dB
steps).
Band (RANGE)
Resistors (A10A2)
128 - 256 MHz
R6
R7
R8
64 - 128 MHz
R12
R13
R14
32 - 64 MHz
R18
R19
R20
Attenuation
Resistance
3 dB
17.8
Ω
287
Ω
287
Ω
4 dB
23.7
Ω
237
Ω
237
Ω
5 dB
31.6
Ω
178
Ω
178
Ω
c. To change attenuation, change all three
resistors associated with the band that's out of
specification. For example, if 64-128 MHz band's
second harmonic is too high, then R13, R12, and R14
will have to be changed. Change attenuation in 1 dB
steps (e.g., to change their attenuation to 5 dB, change
R13 to 31.6
Ω
, R12 to 1782, and R14 to 178
Ω
.)
NOTE
Attenuation should be no higher than
necessary to bring a band's second
harmonic within specification.
Excessive attenuation may reduce
maximum RF output level below +19
dBm.
d.
A26A3C3, C4, C5 and C6 Selection
.
Capacitors may or may not be used; their values are
always 0.22 pF. Select as follows:
1. Set AM switch to PULSE, FREQUENCY
RANGE to 256-512 MHz, and RF ON/OFF to
ON.
2. Connect a spectrum analyzer to MOD OUTPUT
JACK, A26A3J1.
3. Check from 256 to 512 MHz (tune
FREQUENCY TUNE across band). Signals
should always be below -58 dBm.
4. Add or remove capacitors across diodes as
necessary to keep signals below -58 dBm.
Table 5-1. Factory Selected Components
(1 of 2)
Component
Service
Range of
Basis of Selection
Sheet
Values
A8A1R4
18
2-5 k
Ω
See paragraph 5-21.
Select for an indica-
tion on counter with
100 mVrms applied
to COUNTER IN-
PUT.
A10A2R6-8,
11
See paragraph 5-21.
R12-14, and
R18-20
See backdating, Tables 7-1 and 7-2.
5-2
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com