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HOW TO USE TROUBLE-SHOOTING PROCEDURE: Locate the problem on
this table and proceed with the action starting with Step 1. Note, for all DVM
and scope measurements, connect the (-) lead to TP1 (GND).
14.0 700M TROUBLE-SHOOTING AID
700M T
ROUBLE
Step Problem
Action to be Performed
Measure voltage at U6-19 with
Blank
1.
Display*
DVM. It should be at +5.0 ±0.25V.
Measure voltage at Q3 output
lead. (The output is the lead near-
2.
est to the edge of the circuit
board).
Measure voltage at input of Q3. It
3.
should be 6.5V ±.1V.
Check voltage at TP3. It should be
4.
+5.0V ±0.25V.
Check Check U4-25 with a scope.
It should be a 3.58MHz square
5.
wave with levels from 0 to 5 volts.
Replace Y1 crystal and repeat
6.
Step 5.
Measure the voltage at Q1 output.
No +5
It should be +5.0V ±0.25V. (The
7.
volts or
output is the lead nearest to U6).
incorrect
Measure voltage at pin 6 of wire
8.
harness. It should be equal to the
battery or power supply voltage.
Replace Q1 and repeat Step 7.
9.
Unit con-
Measure voltage at U4-28 with
10.
stantly
DVM. It should be -4.3 ±0.2V
read -OL-
Check voltage at U3-8. It should
11.
be +5.0V ±0.25V.
Connect a decade box to the input
and set to 28150 ohms. Measure
12.
voltage at U1-10. It should be
+0.561V ±0.005V.
S
P
HOOTING
ROCEDURE
If Correct
If Incorrect
Proceed to
Proceed to
Step 4.
Next Step.
Check for open
Proceed to
trace between
Next Step.
Q3 and U6-19.
Replace Q3.
Go to step 8.
Proceed to
Go to Step 7.
next step.
Replace U6. If
Replace U4. If
still exists, go
still no dis-
to Step 19.
play, go to
next step.
Done.
Go to Step 19.
Check for open
Proceed to
trace on circuit
next step.
board.
Proceed to
Check wire
next step.
harness for
broken wires.
Done.
Go to Step 19.
Go to step 12. Proceed to
next step.
Replace
Go to Step 7.
U3.
Go to
Proceed to
Step 14.
next step.
30
700M T
ROUBLE
Step Problem
Action to be Performed
Check voltage at U1-5. It should
13.
be +0.561V ±0.005V.
Check voltage at U2-10. It should
14.
be +1.458 ±0.005V.
Check voltage at U2-5. It should
15.
be +0.578V ±0.005V.
Check voltage at wire harness at
16.
pin 3 on circuit board. It should
be +0.460V ±0.005V.
Check voltage at wire harness at
pin 1 on circuit board. It should
17.
be +0.578V ±0.005V.
Check for +5 volts, check R1
through R6, R12 and R13. Also
check harness for loose or broken
18.
wires.
Return unit to factory for repair.
19.
S
P
HOOTING
ROCEDURE
If Correct
If Incorrect
Replace U1.
Go to Step 16.
Go to Step 19. Proceed to
next step.
Replace U2.
Proceed to
next step.
Proceed to
Go to Step 19.
next step.
Go to Step 19. Proceed to
Next Step.
Proceed to
Replace bad
next step.
component. If
problem still
exists, pro-
ceed to next
step.
31
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