Fluke 8020A - Troubleshooting Guide

d.
Use static ground straps to discharge repair
4 - 40.
A troubleshooting guide for the 8020A is given
personnel.
in Table
4-6. To properly use the guide complete the
performance test given earlier in this section and note
e.
Use conductive foam to store replacement or
any discrepancies. Then locate the heading of the
removed
IC's.
procedure in question in the Test and Symptom column
(Table
4 - 6). Under that heading isolate the symptom
that approximates the observed malfunction. Possible
f.
plastic, and styr0f0am causes are listed to the right of the selected symptom.
products from the work area.
Details necessary to isolate
a particular cause can be
derived from the theory of operation in Section
3 and
€5
Use a grounded soldering iron.
the schematic diagram in Section 7.
Table 4 - 6. Troubleshooting Guide
TEST AND SYMPTOM POSSIBLE CAUSE
INITIAL PROCEDURE
BT is displayed when unit is turned on. Low battery,
Q2, U7, U8.
Display blank.
Dead battery, power switch, VR2 shorted,
U8.
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.
Display interconnect, display, or
A/D Converter U8.
Range switches, U6, U7, or display. (Check signals
at U7 to isolate).
Minus sign improperly displayed.
U8.
Display lit but does nt respond to changes in
input.
Reference VR1, crystal Y1, AID Converter U8.
RESISTANCE/CONDUCTANCE TEST
Displayed reading is out of tolerance on at least
Range resistor
U1.
one but not all ranges.
Readings are noisy on all ranges.
Thermistor Rtl
Readings are out of tolerance on high ohms.
RV1, RV2, RV3, RV4 overheated from severe
overload.
Residual reading with test leads open PCB is contaminated (See cleaning procedure,
Section
4).
DC VOLTAGE TEST
Display reading is out of tolerance on 200
mV
Out of calibration (DC), Vref (VR1) in error, U5, U8,
range. S1.
Readings are out of tolerance on all ranges except
Range resistor
U1, U2, U3.
200mV.
AC VOLTAGE TEST
Displayed reading is out of tolerance on 200
mV
Out of calibration (AC), AC converter defective.
range.
2V range is out of tolerance with
1.9V, 5kHz input.
HF adjust
(Cl) out of calibration.
Readings out of tolerance on all ranges except
200mV.
DC CURRENT TEST
Input does not affect display.
U1.
Fuse F1 open, CR1, CR2.
Displayed reading is out of tolerance on one or
If 2000
mA and 200 mA ranges are okay U2 is
more ranges.
defective. Otherwise U3 is defective.
CALIBRATION
DC CAL pot at limit.
VR1, U5 or R6.
AC CAL pot at limit.
U4;
CR5, CR6, R4, AR1, dc calibration.
HF adjust at limit.
S3D, U1, C1, shield not installed.