Fluke 77 Series III Service Manual page 37

77 Series III
Service Manual
1. Turn meter on
Does meter power up?
2. Meter powers up, but
does not come out of
self-test.
3. Meter comes up with
missing segments.
4. Switch meter to V and
apply 3V dc. Does
meter display 3 VDC?
5. Does meter autorange
correctly?
6. Switch meter to V.
Apply 3V @ 500 Hz.
Does meter display
3 VAC?
7. Switch meter to
Apply 100 ohms. Does
meter display 100 ?
8. Switch meter to A.
Apply 300 mA dc. Does
meter display 300 DC?
9. Switch meter to
Does beeper sound
when leads are
shorted?
3-12
ON
YES
YES
NO
YES
NO
ON
YES
ON
YES
YES
NO
.
NO
YES
NO
YES
.
NO
Figure 3-2. Troubleshooting Tree
Check:
a. Power supplies
TP1 = 3.1V dc +/-0.1V
TP3 = 1.5V dc
U1 pin 48 = 6V dc (Battery voltage - TPIV)
(If any of these voltages are high, low, or missing,
replacement of U1 is usually necessary)
b. For loose pins on U1, U2
c. Battery voltage
d. S1 for bad contacts
e. VR1 for 1.2V dc
f. Shield for short to Q3
g. For solder debris/shortd
Check:
a. For loose pins on U1, U2
b. For shorted C5, 6, 7, or 8
c. Contacts of S1
d. For shorted pins on U1, U2
e. Y1 Frequency @ 32.768 kHz
Check:
a. LCD for cracks
b. For contaminated display interconnects or display
contact areas
c. For loose pins on U2
d. For cracks in U2 package
e. Junction of R11 and R12 for 1.6V dc.
Probable cause:
a. RV1 or RV2 or RV3 shorted
b. S1 Contacts bad
c. Z1 open or out of tolerance
d. U1 bad
e. U1 loose/shorted pins
Probable cause:
a. U1 bad
b. S1 bad
Probable cause:
a. U1 bad (also check for loose or shorted pins)
b. S1 bad
c. C9, C11 shorted
Probable cause:
a. S1 bad
b. Q1, Q2 shorted
c. Loose pins on U1, U2
d. U1 bad
Probable cause:
a. F1, F2 open
b. S1 bad
c. R7 open
d. Open land patterns in current path
Check:
a. Connector contact points
b. For correct signal at contact points. Should be 4.1 kHz
waveform. (If above checks are good, LS1
replacement is necessary.)
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