Chapter 8 451
IF Section
Cal Oscillator Assembly (P/O A4)
NOTE If error messages ERR 581 AMPL or ERR 582 AMPL appears, refer to
error message ERR 582 AMPL in Chapter 6 and perform the procedure
provided.
1. The oscillator output frequency should exceed 11.5 MHz if the CAL
OSC TUNE line, A4U804 pin 14, exceeds +9 V. The oscillator
frequency should be less than 9.9 MHz if CAL OSC TUNE is less
than −9 V. The oscillator only operates when CALOSC_OFF is low (0
V).
2. If the cal oscillator remains locked (no error code ERR 499 displayed)
but does not have the correct output level, troubleshoot the output
leveling circuitry (function blocks AA, AB, and AC) or output
attenuator (function block AD).
Cal Oscillator Unlock at Beginning of IF Adjust
1. Press LINE to turn the spectrum analyzer off and then on. The words
IF ADJUST STATUS appear on the display 10 seconds after the
instrument is turned on (assuming the rest of the instrument is
working correctly). Immediately observe the lower right corner of
the display for error messages. If the message ERR499 CAL UNLK
appears (before errors ERR 561, ERR 562 and ERR 565), the cal
oscillator is unable to phase-lock. Expect to see the ERR 499 message
for only about 1 second.
2. If the spectrum analyzer registers an unlocked cal oscillator,
continue with step 3 to verify the presence of externally supplied
signals.
3. Check A4U811 pin 9 for a 100 kHz TTL-level square wave verifying
operation of A4U811, A4Q802, and the 10 MHz input signal from
A4J7.
4. Check the +15 VF, +5 VF and −15 V power supplies, and +10 V
reference on the A4 assembly.
5. Check that A4U807 pin 5 (CALOSC_OFF) becomes TTL low (0 V) at
the start of a FULL IF ADJ (press
CAL and FULL IF ADJ). The phase
modulation output at A4U804 pin 8 should also remain at 0 volts. If
these checks are correct, troubleshoot blocks V, W, X, and Y. See
Figure 8-21 on page 463, A4 Log Amplifier/Cal Oscillator Block
Diagram (2 of 2).
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