2. Service
Assembly/Module Diagnostic Trees (Diagnostic Section 3)
86
A2 Thermistor Diagnostic Tree
This functional subsection describes the A2 thermistor diagnostic tree for the
5071A Primary Frequency Standard. Performance of these tests is indicated
by the presence of either a self-test or fatal error that reports a thermistor
fault.
3.1.2.1.0 CBT Thermistor Resistance Test
1 Power off the 5071A.
2 Unplug cable from A2J2.
3 Use a DMM to measure the resistance between pins 6 and 7 on cable.
QUESTION: Is the resistance measured between 200 and 250 k?
If No: Recheck results and DMM, then replace CBT.
If Yes: Go to, 3.1.2.1.1.
3.1.2.1.1 CBT Thermistor Ground Test
1 Use a DMM to measure the resistance between cable pins 7 and 11.
QUESTION: Is the resistance less than 1 ?
If No: Recheck results and DMM, then replace CBT.
If Yes: Go to, 3.1.2.1.2.
3.1.2.1.2 Thermistor Monitor Test (No Current)
1 Remove instrument power.
2 Remove A2 CBT Controller.
3 Install long extender board (05071-60052) into A2 slot.
4 Turn on the 5071A.
5 Use SCPI command syst:print?.
(Terminal-to-instrument via RS-232C data communication required.)
QUESTION: Is thermistor between -0.05 and +0.05 C
If Yes: Go to, 3.1.2.1.3.
If No: Remove power, replace A7, and retest.
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