TM 9-4935-601-14-7&P
Model 8640B
INSTRUMENT MODIFICATIONS
7-48.
A10A2 RF Divider Assembly Improvement
(Serial Prefix 1313A and Below)
7-49.
On instruments with serial number prefix 1313A
and below, subharmonic rejection can be improved if
the fourth RF divider is wired so that it is off when the
RF output is taken from the third divider. Refer to
Figure 7-11 and Service Sheet 11 and proceed as
follows:
1. Remove top cover of instrument (see Service
Sheet F for procedure).
2. Remove 14 4-40 pan-head screws that secure
cover of A10 Divider/Filter Assembly casting
(screws are marked "*" on cover). Note that the
two center screws are longer than the others.
3. Remove cover from casting.
4. Remove 12 4-40 pan-head screws that secure
A1OA2 RF Divider Assembly. Remove
A10OA2 and riser board (A10OA3) by lifting at
the riser.
5. Solder a 1/2-inch length of insulated wire
between pin 3 of U18 and the end of R16 (5.11
k
Ω
) that is nearest U18. Refer to Figure 7-11.
6. Replace A10OA2 and A10OA3 and check that
there is no output from U18 (pin 1 or 13) when
in the 32 to 64 MHz range. Use a high
impedance 50 MHz oscilloscope.
7. Continue reassembly of the instrument and
check for proper operation on all frequency
ranges.
Figure 7-11. A1OA2 RF Divider Assembly Modification
7-85
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com