E F Johnson Company 2422001-1 Benutzerhandbuch
SERVICING
8-3
August 2000
Part No. 001-2001-200
Example: 150.250 MHz (receive)
Prescaler Div No = 64 + (40
÷
507) = 64.106666
Measure the prescaler input frequency at f
in
, pin
11. Then measure the output frequency at TEST 2, pin
13 and calculate the divide number. If the VCO is not
locked on frequency, the divide number should still be
correct. The measured frequencies may not be exactly
as calculated due to counter accuracy and resolution
limitations.
13 and calculate the divide number. If the VCO is not
locked on frequency, the divide number should still be
correct. The measured frequencies may not be exactly
as calculated due to counter accuracy and resolution
limitations.
8.2.5 CALCULATING "N " AND "A " COUNTER
DIVIDE NUMBERS
"N" Counter
N Counter Divide Number =
Integer (VCO Freq. (MHz)
Integer (VCO Freq. (MHz)
÷
0.4)
6.25 kHz (64)
÷
1 MHz = 0.4
EXAMPLE: 150.025 MHz (receive)
VCO freq = 150.025 + 52.95 = 202.975 MHz
N Cntr Div No = 202.975
N Cntr Div No = 202.975
÷
0.4 = 507.4375
Integer (whole no.) of 507.4375 = 507
EXAMPLE: 150.250 MHz (transmit)
N Cntr Div No = 150.250
÷
0.4 = 375.625
Integer (whole no.) of 375.625 = 375
"A" Counter
A Counter Divide Number =
(VCO freq (MHz)
A Counter Divide Number =
(VCO freq (MHz)
÷
.00625) - (N Cntr Div No x 64)
EXAMPLE: 150.025 MHz (receive)
A Cntr Div No = (202.975
÷
.00625) - (507 x 64)
= 32,476 - 32,448
= 28
= 28
EXAMPLE: 150.250 MHz (transmit)
A Cntr Div No = (150.250
÷
.00625) - (375 x 64)
= 24,040 - 24,000
= 40
= 40
8.3 RECEIVER SERVICING
To isolate a receiver problem to a defective sec-
tion, start by checking the DC voltages shown in Sec-
tion 6.1.2 and on the schematic diagram (Section 10).
If that does not indicate the problem, perform the per-
formance tests in Section 7.1 to isolate the problem. If
the synthesizer is out of lock, the receiver is also non-
functional because the first injection and IF signals
will be incorrect.
tion 6.1.2 and on the schematic diagram (Section 10).
If that does not indicate the problem, perform the per-
formance tests in Section 7.1 to isolate the problem. If
the synthesizer is out of lock, the receiver is also non-
functional because the first injection and IF signals
will be incorrect.
8.4 TRANSMITTER SERVICING
To isolate a transmitter problem to a defective
section, start by checking the DC voltages shown in
Sections 7.2.2 and on the schematic diagram (Section
10). If that does not indicate the problem, perform the
performance tests in Sections 7.2 and 7.3 to isolate the
problem. If the synthesizer is out of lock, the exciter is
also nonfunctional because the software will not allow
the repeater to transmit.
Sections 7.2.2 and on the schematic diagram (Section
10). If that does not indicate the problem, perform the
performance tests in Sections 7.2 and 7.3 to isolate the
problem. If the synthesizer is out of lock, the exciter is
also nonfunctional because the software will not allow
the repeater to transmit.
8.5 POWER SUPPLY SERVICING
The power supply is a switch mode type with
very high voltages. It is recommended that the power
supply be returned to the factory for servicing (see
Section 1.8). Customers that desire to do their own
repairs can obtain a service manual for the power sup-
ply, Part No. 004-2000-810.
supply be returned to the factory for servicing (see
Section 1.8). Customers that desire to do their own
repairs can obtain a service manual for the power sup-
ply, Part No. 004-2000-810.