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TM 55-4920-412-13&P
(12)
Connect Digital multimeter to test loop 3
(+) and 117 (-) on extender board. Set Power to ON.
Digital multimeter will indicate between +4.5 and +5.5
Vdc. If not, see Troubleshooting Table 4-37.
(13)
Set Power to OFF and disconnect Digital
multimeter from test loops 3 and 117 on extender board.
(14)
Connect Oscilloscope between test loops
114 (+) and 117 (-) on extender board. Set Power to
ON. Oscilloscope will display a negative-going pulse
with an amplitude of 4.5 to 5.5 Vp-p, and a duration of
approximately
31
milliseconds.
If
not,
refer
to
troubleshooting table 4-37.
(15)
Set Power to OFF and repeat Technique
(13) above using test loop 115 (+) on extender board.
Oscilloscope will display a rectangular wave 4.5 to 5.5
Vp-p. Oscilloscope will indicate approximately 31
milliseconds duration. If not, see troubleshooting table
4-37.
(16)
Set Power to OFF and reinstall monitor
board NO. 1 (A7).
(17)
Connect Digital multimeter between TEST
POINTS 3 (+) and SDC (-) on front panel of unit tester.
(18)
Set Power to ON. Digital multimeter will
indicate between 4.5 and 5.5 vdc. Set Power to OFF
and disconnect from TEST POINT 3(+) and reconnect to
TEST POINT 4 (+). Set Power to ON. Indications will
be as specified for TEST POINT 3. Observe that MUX
Analog, MUX Digital and Digital O/P Monitor lamps are
ON. If indications are normal go to step (25). If not,
perform (19) thru (25) below.
(19)
Set Power to OFF. Remove monitor
board NO. 2 (A8) 3 and carefully reinstall using extender
board.
(20)
Connect Digital multimeter to test loops 3
(+) and 117 (-) on extender board. Set Power to ON.
Digital multimeter will indicate between +4.5 and +5.5
Vdc. If not, see Troubleshooting Table 4-38.
(21)
Sct Power to OFF and disconnect digital
multimeter from test loops 3 and 117 on extender board.
Table 4-38. Troubleshooting Monitor Board No. 2 (AS) Test Points, Shift Reg Monitor, Digital O/P, Mux Analog, Mux
Digital, Digital Mux, and Analog Mux Circuits.
NOTE
Troubleshoot Monitor Board A7 (Table 4-37) Before Making Checks Below.
Trouble
Probable Cause
Remedy
5 vdc low or missing (Input)
Logic Power Supply A3 Input 8V
Replace boards (A3) or (A4). See figs
(Test loop 3)
missing to Regulator Board (A4) or
FO-7 and FO-8.
Output 5V missing from (A4).
DIGITAL O/P MONITOR does not
U38,U35,U36,U34,U35,U37,U33,
Replace Board (A8), figures 4-24 and
light
CR7,CR8,U32,Q2,U24,U25,U26,
FO-16.
(Test loop 102)
U30,U27,U28,U9, Board (AS).
Test Points 1 2. missing 5 vdc or
Monitor Board NO 1. (A7) or Moni-
Replace board (A7) or board (AS).
(Test Loops 91 and 94)
tor Board NO. 2 (A8). (Check (A7)
See figs 4-23, 4-24, FO-15, FO-16.
Board First).
Test Points 3, and 4 missing 5 vdc or
Monitor Board NO. 2 (A8).
Replace board (A8).
(Test loops 103 and 104)
See figures 4-24, FO-16.
MUX ANALOG MONITOR does
CRR,CRI0,CRI 1,U39,U40,U41,
Replace board (A8). See figures 4-24,
not light
U21,U22,Q3, Board (AS).
FO-16.
(Test loop 28)
SHIFT REO MONITOR does not
U1 thru U23, Q1, CR1 thru CR4,
Replace board (A8), or (A7). See figs.
light
Board (AS), and Board (A7).
4-23, 4-24, FO-15, FO-16.
(Test loop 93)
MUX DIGITAL does not light
U41,UQ.CR13, Board (A8).
Replace board (AS). See figs 4-24,
(Test loop 30)
FO-16.
4-68 Change 2
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