EFJohnson 9800 SERIES Manuale Utente
SERVICING
4-5
February 2001
Part No. 001-9800-001
4.3.5 DETERMINING SYNTHESIZER COUNTER
DIVIDE NUMBERS
NOTE: For more information on the operation of the
counters in U801, refer to Section 3.7.5.
counters in U801, refer to Section 3.7.5.
Overall Div No. (K) = VCO freq ÷ .050
Example: 813.4875 ÷ .050 = 16,269.75
“A” Divide No. = 64 x Fraction (Integer K ÷ 64)
Example: 16,269 ÷ 64 = 254.20312
Fraction 254.20312 = 0.20312
64 x 0.20312 = 13
64 x 0.20312 = 13
“N” Divide No. = Integer [K ÷ 64] – A
Example: Integer 254.20312 = 254
254 – 13 = 241
Fractional-N Div No. = (Fraction K) x 8
Example: Fraction 16,269.75 = 0.75
0.75 x 8 = 6
4.4 RECEIVER SERVICING
To isolate a receiver problem to a specific
section, check the DC and RF voltages shown on the
schematic diagram.
schematic diagram.
With UHF models only, the front end filter
frequency shift inputs on U800, pins 6 and 7 should be
as follows (L = 0V, H = 5V):
as follows (L = 0V, H = 5V):
4.5 TRANSMITTER SERVICING
To isolate a transmitter problem to a specific
stage, check the DC and RF voltages shown on the
schematic diagram.
schematic diagram.
4.6 AUDIO/LOGIC BOARD SERVICING
4.6.1 DIGITAL CIRCUITS
Because of the complexity and dynamic operation
of the digital portion of the audio/logic board,
servicing may be difficult. Special test equipment and
knowledge of the operating software are usually
needed to isolate a problem. Therefore, if a problem is
suspected with the digital circuitry, it may be best to
first make sure that the proper supply voltages are
present and then replace the audio/logic board.
servicing may be difficult. Special test equipment and
knowledge of the operating software are usually
needed to isolate a problem. Therefore, if a problem is
suspected with the digital circuitry, it may be best to
first make sure that the proper supply voltages are
present and then replace the audio/logic board.
4.6.2 ANALOG CIRCUITS
The analog circuits on the audio/logic board can
be checked by measuring the AC and DC voltages
shown on the schematic diagram.
shown on the schematic diagram.
Frequency
Shift F1
(Pin 6)
Shift F2
(Pin 7)
430-440 MHz
H
H
440-450 MHz
L
H
450-460 MHz
H
L
460-470 MHz
L
L
470-480 MHz
H
H
480-491 MHz
L
H
491-502 MHz
H
L
502-512 MHz
L
L