Heat-Prober
®
Platinum-RTD Thermometers User Manual
36
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 TROUBLE SHOOTING PROCEDURE
Step
Problem
Action to be Performed
If Correct
If Incorrect
1.
Blank
Display*
Measure voltage at U6-19 with DVM.
It should be at +5.0 ±0.25V.
Proceed to
Step 4.
Proceed to
Next Step.
2.
Measure voltage at Q3 output lead.
(The output is the lead nearest to the
edge of the circuit board).
Check for open
trace between
Q3 and U6-19.
Proceed to
Next Step.
3.
Measure voltage at input of Q3. It
should be 6.5V ±.1V.
Replace Q3.
Go to step 8.
4.
Check voltage at TP3. It should be
+5.0V ±0.25V.
Proceed to
next step.
Go to Step 7.
5.
Check U4-25 with a scope. It should
be a 3.58MHz square wave with levels
from 0 to 5 volts.
Replace U6. If
still exists, go to
Step 19.
Replace U4. If
still no dis- play,
go to next step.
6.
Replace Y1 crystal and repeat
Step 5.
Done.
Go to Step 19.
7.
No +5
volts or
incorrect
Measure the voltage at Q1 output. It
should be +5.0V ±0.25V. (The output
is the lead nearest to U6).
Check for open
trace on circuit
board.
Proceed to
next step.
8.
Measure voltage at pin 6 of wire
harness. It should be equal to the
battery or power supply voltage.
Proceed to
next step.
Check wire
harness for
broken wires.
9.
Replace Q1 and repeat Step 7.
Done.
Go to Step 19.
10.
Unit
constantly
read -OL-
Measure voltage at U4-28 with
DVM. It should be -4.3 ±0.2V
Go to step 12.
Proceed to
next step.
11.
Check voltage at U3-8. It should be
+5.0V ±0.25V.
Replace
U3.
Go to Step 7.
12.
Connect a decade box to the input
and set to 28150 ohms. Measure
voltage at U1-10. It should be
+0.561V ±0.005V.
Go to Step
14.
Proceed to
next step.
