Fluke 8062A Instruction Manual page 84

8062A
Instruction Manual
One way to check the input circuitry is to attach a high impedance
(>1000 M ) DMM at the input of the 8062A a/d converter, U3-6.
You can do a lot of troubleshooting without the LCD and
microcomputer pcb installed. Although there will be no display and the
a/d converter will not work, the power supplies still work so you can
check the input circuitry, the diode test and ohms sources, and the ac
converter. Another advantage is that you gain access to all the pins on
U3 without having to turn the main pcb over.
You can troubleshoot the input circuitry with U3 removed (be sure to
disconnect the battery before removing U3). Since U3 controls the
power supply, removing U3 will cause the ac converter and diode test
source to stop working. However, it will also eliminate any power
supply leakages that might be affecting the input circuitry. Since the
input protection, input divider and ohms reference resistors, amps
protection, current shunts, and a/d input circuits consist of passive
components (refer to the schematic in Chapter 7) you can check them
without having U3 installed.
Test and Symptom
Power On/Microcomputer and
Display Test
No display
Missing LCD segments
All LCD segments stay on
Entire display is dim
Some display segments are
dim or ghosting
Power Supply
VDD (voltage between
TP7 and common)
5.2 0.12V
4-22
Table 4-6. Troubleshooting Guide
Possible Cause/Suggestions
Dead battery, battery connections,
J4, power supply circuitry.
Display interconnect.
Microcomputer connector, U5, U3,
pcb lands open.
Low battery, power supply low,
display interconnect.
Display interconnect, contamination
on pcb connector or LCD.
U3, Q1, VR1