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5-6
MAINTENANCE
5.
Connect a 1.9
Ω
standard to the UUT using the clip
leads.
6.
Verify that the display of the UUT displays the actual
standard value ±2 counts.
7.
Disconnect the resistance standard.
5.5
Troubleshooting
Following are possible symptoms, diagnosis, and repair
suggestions for use in trouble-shooting (the most likely
causes are listed first).
Symptom
Faulty
Component
Repair
No Display
Batteries
Power cord
Power
switch
U6
Check for batteries installed & polarity.
Check the power cord is plugged in.
Check the power switch is ON.
Check for a square wave between pin 4 & 40 of
U4, if present, replace U6.
Battery
won’t
charge
Connections
Batteries
Fuse
Fuse (F1)
U1
R1/R101
D5
Remove battery cells and bend contact arms
inward to ensure better contact with the battery
cells.
Clean connections if required.
Try a new set of batteries.
Check fuses.
Check for 12 VDC across C1. If not check for
mains on pins 1 & 2 of U8. If not replace U8. If
ok, check for aprox. 6 VDC (ref. to common) at
the output of U1. If not, replace U1.
If above ok, check for approximately 4.5 VDC
(ref. to common) at the anode of D5, if not,
replace R1/R101.
If above ok, check for approximately 3.6 VDC
(ref. to common) at the cathode of D5, if not,
replace D5.
Display
reads zero
with cables
connected
to a good
resistor
Current o/p
Kelvin Clip
U9/U11/Q1
U10/U9
Check for proper current o/p bI and -
I.
If above ok, check the Kelvin cable for
continuity from each side to the banana plug.
If no current, troubleshoot the const. current
circuit and replace U11 or other component(s)
if defective.
