HP 8901B - Page 272

Model 8901B Service
TROUBLESHOOTING
General
Procedures for checking the Digital and Power Supply Sections 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 connectors
is insufficient. Hand-tightened connectors can work loose and cause reduced
performance
or malfunctions.
Equipment
Digital Testmxtender Board ................................................. HP 08901-60081
Oscilloscope
...................................................................... HP 1740A
Signature Analyzer
................................................................ HP 5005A
Voltmeter
........................................................................ HP 3455A
a Time Base Reference Check
1. Disconnect any input to the rear-panel TIME BASE 10 MHz INPUT.
2. Connect high-impedance, dc coupled oscilloscope to AllJ5 (INT 10 MHZ OUT). The waveform
should be a TTL square wave with a period of
100 ns. If faulty, see Service Sheet 22 and check
the
10 MHz Time Base Reference Oscillator.
3. Check A11TP4 (TB) with an oscilloscope. The waveform should be TTL pulses with a period of
160
ps. If faulty, see Service Sheet 22 and check the Time Base Divider.
@ Counter Check
NOTE
This check assumes that the @ Time Base Reference Check give positive
results.
For Option 002, disconnecting the cable from the time base reference
halts the Controller.
1. Connect a jumper cable between AllJ5 (INT 10 MHZ OUT) and AllJl (+8 IN). Key in 46.4
SPCL. This switches the Counter to measure the HF
VCO divided by 8. The display should read
10000002Zl.
If faulty, see Service Sheet 23.
2. Disconnect the jumper from AllJl and connect it to AllJ3 (IF IN). Key in 46.2 SPCL. This
switches the Counter
to measure the IF. The display should read 1000000~1. If faulty, see Service
Sheet 23 and check the Input Selector.
3. Disconnect the jumper from AllJ3 and connect it to AllJ2 (10 MHZ IN). Key in 46.3 SPCL.
This switches the Counter to measure the output of the FM Calibrator. The display should read
10000002Zl.
If faulty, see Service Sheet 23 and check the Input Selector.
4. Remove the jumper cable. Short AllTPl (GND) to A11TP6 (VM GATE). Key in 46.2 SPCL.
This switches the Counter to measure the
10 MHz time base reference via the Voltage-to-Time
Converter input. The display should read 1000000fl.
If faulty, see Service Sheet 23 and check
the Input Selector and Voltmeter Gate logic.
Service Sheet BD5 8D-53