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10.0 392M TROUBLE-SHOOTING AID
10.1 Scope
This section describes basic diagnostics to find the majority of the problems
with malfunctioning 392M units.
Equipment Required:
1. Wahl 392M Calibrator (Model Number CAL392-HT)
2. 4- Digit DVM, Fluke 8600A or equivalent.
3. Oscilloscope.
4. Power supply, Power/mate BPA-10c or equivalent.
10.2 Procedure
Make certain that the 392 unit experiencing the problem has been properly
set-up, per Section 6.0, before proceeding to this section.
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 CR1 Cathode (GND).
392 S
ERIES
T
ROUBLE
S
HOOTING
P
ROCEDURE
Step Problem
Action to be Performed
If Correct
If Incorrect
1.
Blank
Display*
Measure voltage at U6-19 with
DVM. It should be at +4.3 ±.2V.
Proceed to
Step 3.
Proceed to
Step 2.
2.
*
Repeat above measurement, but
with (+) lead at Q4 emitter.
Check for
open trace
between Q4
emitter and
U6-19.
Go to Step 4.
3.
Check U4-25 with an oscilloscope.
It should be a 3.58MHz square
wave with levels from 0 to 5 volts.
Replace U6. If
still no display,
go to Step 9.
Replace U4. If
still no dis-
play, go to
Step 7.
4.
*
Check voltage at Q4 collector. It
should be equal to the battery
voltage or applied voltage from
test power supply.
Proceed to
next step.
Check for
open trace
from Pin
5 to Q4 (C).
5.
Check voltage on junction of R30
and CR5 cathode. Should be
+5.000 ± .005V.
Proceed to
next step.
Go to Step 8.
6.
*
Check voltage on junction of R30
and Q4 base. It should be between
+4.7 and +4.9 volts.
Replace Q4.
Replace R30.
7.
Replace Yl crystal and repeat Step
3.
Done.
Go to Step 16.
8.
No +5000
volts or
incorrect
Measure voltage at U2-2. It should
be +2.5 volts ± 0.1V.
Go to Step 11. Proceed to
next step.
9.
Measure voltage at pin 5 of wire
harness. It should be equal to the
battery or power supply voltage.
Proceed to
next step.
Check wire
harness for
broken wires.
10.
Check voltage at U7-2. It should
be +2.5 volts ± 0.1V.
Proceed to
next step.
Replace U7.
11.
Check voltage at Q2 between base
and emitter, there should be
approx. a 0.7V drop.
Replace
Q2. If still
incorrect go to
Step 16.
Replace U2
and check
CR3, CR4,
R19, R20 &
R22.
12.
Unit con-
stantly
reads -
OL-
Measure voltage at U4-28 with
DVM. It should be -4.3 ± 0.1V.
Proceed to
next step.
Proceed to
Step 14.
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