Maintenance
Troubleshooting
5
5-27
Table 5-7. Troubleshooting Guide (cont)
Test and Symptom Possible Cause/Suggestions
Resistance/Conductance Test
(cont)
CR1 supplying proper current
but reading off
Check values of the reference
resistors for the range not working.
Check voltage drops across the
known and unknown resistors and
make sure the ratio works properly.
Low range readings correct,
high range readings off
Q3 and Q4 leak-check by seeing if
MΩ reads OL with open input, or
conductance reads 0 ±1.0 nS with
open input. Main pcb contaminated -
clean carefully and check
performance.
MΩ range correct, but
conductance not working
U3
Conductance reading >1.0 nS
with open input
Main pcb contamination, U3
contamination
Current Test
Constant reading of 0.00 Check fuses F1 and F2 with fuse
check procedure in Chapter 2-4.
Fuses F1 and F2 good, but
current readings off
Switches and resistors in current
shunt.
High crest-factor ac current
readings off
U1
Frequency Test
AC volts readings correct, but
frequency readings off
Check to see if ac signal at input
arrives at U3-4 (inverting input to the
frequency comparator in U3). If it is,
check frequency calibration. If it is
not, check R31, C27, Z7 and S1A.
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