392M Trouble-Shooting Aid; Scope; Procedure - Wahl HEAT-Prober 392HP Instruction Manual

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).
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392 S T
ERIES ROUBLE
Step Problem Action to be Performed
Blank Measure voltage at U6-19 with
1.
DVM. It should be at +4.3 ±.2V.
Display*
Repeat above measurement, but
with (+) lead at Q4 emitter.
2. *
Check U4-25 with an oscilloscope.
It should be a 3.58MHz square
3.
wave with levels from 0 to 5 volts.
Check voltage at Q4 collector. It
should be equal to the battery
4. *
voltage or applied voltage from
test power supply.
Check voltage on junction of R30
5. and CR5 cathode. Should be
+5.000 ± .005V.
Check voltage on junction of R30
6. * and Q4 base. It should be between
+4.7 and +4.9 volts.
Replace Yl crystal and repeat Step
7.
3.
No +5000
Measure voltage at U2-2. It should
8. volts or be +2.5 volts ± 0.1V.
incorrect
Measure voltage at pin 5 of wire
harness. It should be equal to the
9.
battery or power supply voltage.
Check voltage at U7-2. It should
10.
be +2.5 volts ± 0.1V.
Check voltage at Q2 between base
and emitter, there should be
11. approx. a 0.7V drop.
Unit con- Measure voltage at U4-28 with
stantly DVM. It should be -4.3 ± 0.1V.
12.
reads -
OL-
S P
HOOTING ROCEDURE
If Correct If Incorrect
Proceed to Proceed to
Step 3. Step 2.
Check for Go to Step 4.
open trace
between Q4
emitter and
U6-19.
Replace U6. If Replace U4. If
still no display, still no dis-
go to Step 9. play, go to
Step 7.
Proceed to Check for
next step. open trace
from Pin
5 to Q4 (C).
Proceed to Go to Step 8.
next step.
Replace Q4. Replace R30.
Done. Go to Step 16.
Go to Step 11. Proceed to
next step.
Proceed to Check wire
next step. harness for
broken wires.
Proceed to Replace U7.
next step.
Replace Replace U2
Q2. If still and check
incorrect go to CR3, CR4,
Step 16. R19, R20 &
R22.
Proceed to Proceed to
next step. Step 14.
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