HP 8901B - Page 249

Model 8901B Service
TROUBLESHOOTING
General
Procedures for checking the IF Section of the instrument are given below. The blocks or points to check
are marked on the block diagram by a hexagon with a check mark and a number inside, for example,
@ . Before performing any check, perform all the checks on Service Sheet BD1.
Tighten SMC connectors to 0.6 N. m (5 in. lb). Hand tightening of connec-
tors is insufficient. Hand-tightened connectors can
work loose and cause
reduced performance
or malfunctions.
Equipment
Audio Synthesizer. ................................................................ HP 3336C
Oscilloscope
...................................................................... HP 1740A
SignalGenerator
.................................................................. HP 8640B
a FM IF Buffer Check
1. Perform the Input Mixer and IF Check on Service Sheet BD2.
@) IF Detector Check
NOTE
This check assumes that the (J1) FM IF Buffer Check gives positive results.
1. Set the signal generator to 20 MHz CW at 0 dBm. Connect its RF output to the Modulation
Analyzer’s INPUT.
2. Connect an ac coupled oscilloscope to rear-panel IF OUTPUT. Switch the input impedance of
the oscilloscope to
5052 or terminate the input in 500 using a tee.
3. Press the blue key, then press INSTR PRESET (the AUTOMATIC OPERATION key) to preset
the instrument. Key in 20 MHz. If Error 01 appears, press MHz again. Key in 1.3 SPCL to set
the attenuation range
to 20 dB. Adjust the signal generator level for a 100 mVpp waveform on
the oscilloscope.
4. Key in 49. S (Shift) 3 SPCL. This causes the IF level to be displayed. The display should read
between 0.85 and 0.95. If it does not, see Service Sheet 9 and check the IF Peak Detector.
5. Switch signal generator’s RF off.
6. Press CLEAR to clear the IF Present Latch. Key in 0.0 S (Shift) 4 SPCL. The display now reads
the IF Present status. The display should read 000000.0000. If faulty, see Service Sheet 9 and
check the
IF Present Detector.
7. Switch the signal generator’s RF on. The display should read 000001.0000 indicating that IF has
been detected. If faulty, see Service Sheet 9 and check the IF Present Detector.
Service Sheet BD3 8D-29