Troubleshooting Guide - Fluke 8020A Instruction Manual

d. Use static ground straps to discharge repair
personnel.
Use conductive foam to store replacement or
e.
removed IC's.
f.
products from the work area.
Use a grounded soldering iron.
TEST AND SYMPTOM
BT is displayed when unit is turned on.
Display blank.
DISPLAY TEST
One or more segments will not light through
entire test.
Decade inoperative or one or more segments
always lit.
Improper decimal point indication.
Minus sign improperly displayed.
Display lit but does nt respond to changes in
input.
Displayed reading is out of tolerance on at least
one but not all ranges.
Readings are noisy on all ranges.
Readings are out of tolerance on high ohms.
Residual reading with test leads open
DC VOLTAGE TEST
Display reading is out of tolerance on 200 mV
range.
Readings are out of tolerance on all ranges except
AC VOLTAGE TEST
Displayed reading is out of tolerance on 200 mV
range.
2V range is out of tolerance with 1.9V, 5kHz input.
Readings out of tolerance on all ranges except
DC CURRENT TEST
Input does not affect display.
Displayed reading is out of tolerance on one or
more ranges.
CALIBRATION
DC CAL pot at limit.
AC CAL pot at limit.
HF adjust at limit.
4-40.
in Table 4-6. To properly use the guide complete the
performance test given earlier in this section and note
any discrepancies. Then locate the heading of the
procedure in question in the Test and Symptom column
(Table 4-6). Under that heading isolate the symptom
that approximates the observed malfunction. Possible
causes are listed to the right of the selected symptom.
Details necessary to isolate a particular cause can be
derived from the theory of operation in Section 3 and
the schematic diagram in Section 7.
Table 4-6. Troubleshooting Guide
Low battery, Q2, U7, U8.
Dead battery, power switch, VR2 shorted, U8.
Display interconnect, display, or A/D Converter U8.
Range switches, U6, U7, or display. (Check signals
at U7 to isolate).
Reference VR1, crystal Y1, AID Converter U8.
Range resistor U1.
Thermistor Rtl
overload.
PCB is contaminated (See cleaning procedure,
Section
Out of calibration (DC), Vref (VR1) in error, U5, U8,
Range resistor U1, U2, U3.
Out of calibration (AC), AC converter defective.
HF adjust ( C l ) out of calibration.
Fuse F1 open, CR1, CR2.
If 2000 mA and 200 mA ranges are okay U2 is
defective. Otherwise U3 is defective.
U4; CR5, CR6, R4, AR1, dc calibration.
A troubleshooting guide for the 8020A is given
POSSIBLE CAUSE
4).