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5.0 MAINTENANCE/REPAIR
The HEAT-Prober instrument may be recalibrated, or adjusted for a particular
probe in the field by following the directions in Section 6.0. However, it is
recommended that calibrations and repair be done at the factory. Return the
HEAT-Prober in its foam package with a description of symptoms, and a
repair estimate will be made for your approval.
The best way to check the functioning and calibration condition of the HEAT-
Prober is to use the Wahl accessory Calibrator Models Numbers CAL392HT
or CAL392LT, which plug right into the probe connection and provides five
key calibration points. (See Figure 5-1). The calibrator has a set of precision-
wound resistors which are measured at the factory against a NIST traceable
standard. The WAHL calibrator is a convenient instrument to determine
whether a problem is in the probe or the meter. If the meter checks on all 5
calibration points within tolerance, for example, then one will know that the
probes are at fault.
The most common maintenance problem
is battery failure, evidenced by no dis-
play. NiCad battery failure and prevention
of this problem are noted in Section 2.4.
If you suspect a dead battery:
1. Plug in the recharger and
allow to recharge for 12 hours. If batter-
ies fail to recharge after this time:
2. Open the battery compart-
ment lid on the bottom of the instrument.
Unplug the battery. Using a DVM, check
voltage with a 16 ohm load. If the voltage
drops rapidly it indicates a fault in the
battery.
3. With the convenient detach-
able plug, the battery pack Model
Number 11681-1 or 11681-2 can be easi-
ly replaced by a new one. For emergen-
cies it is possible to use a 9-volt transis-
tor battery to power the HEAT-Prober (but
one must make a special connection).
Expected continuous running time on 9-
volt alkaline battery is about 3 hours, for
LED display or 6 hours for LCD display.
Figure 5-1. 392M Platinum Heat
Prober with Wahl Calibrator
Model Number CAL392HT.
6.0 SET-UP AND CALIBRATION
6.1 Equipment Needed
A. Digital voltmeter, Fluke 41/2 digit Model 8600A or equivalent.
B. Wahl Platinum Calibrator (Model Number CAL392HT or CAL392LT) or
General Radio decade box, Model 1433-1 (or equivalent) with standard coil
cord (Model 10434-01 or 10434-02) cable as used with Wahl probes.
C. Power supply — Powermate, Model OPA-1OC or equivalent.
6.2 Voltage Regulator Adjustment (Note: Meters with serial numbers S/N
3445 and higher, or N Series,do not require adjustment of voltage regulator.)
Remove the 4 screws from the bottom of the case, then remove the top
cover. You will note the adjustment points as shown in Figure 6-1.
1. Initially the 392M should be set-up with an external power supply
(rather than a battery) so that the current can be limited to no more than 120
milliamperes.
2. Connect the plus (+) DVM lead to C-10 junction common with Q2.
Connect the minus (-) lead to the cathode lead of CR1.
3. Apply power to the 392M using an external power supply with the
voltage set at 6.5V and current limit set at 120 milliamperes. Connect power
supply (+) to U1-1 and (-) to CR1 - cathode. Adjust R21 for voltage reading
of e5.000 volts on the DVM.
4. When the 392M has been mounted in its case and connected to a
5-battery pack, the DVM is connected as described above and the +5.000
adjustment checked and trimmed if necessary.
6.3 Low Battery Adjustment and Testing
1. Connect DVM (-) to CR1 Cathode and (+) to upper side of R24.
2. Adjust R37 clockwise or counterclockwise until DVM reads 2.11 volts.
3. Disconnect DVM.
4. DISCONNECT BATTERY PACK. Low Battery indicator must be per-
formed with an external variable power supply. Start with 6 volts and slowly
decrease the voltage toward 5.8 volts.
When the battery threshold is reached, a small “L” should appear in the most
significant digit position of the 392HP, 392E and 392M display. “Lo Bat”
appears in the display of the 392EX, 392MX, 392EVX and 392MVX. The actu-
al value of the low battery voltage threshold may vary from 5.45 volts to 5.55
volts.