1. Inoperative Fan:
Open the door. Place your hand near the grill at the top rear of the
chamber and check for air circulation. If there is no air circulation, the
fan motor is malfunctioning. Contact Technical Services.
2. Burned-out heater:
To check this, the control panel cover must be removed.
Warning
Hazardous high voltage conditions exist inside control panel.
Turn ‘OFF’ line switch on front panel and unplug line cord.
s
Remove all screws that fasten the cover. Locate nylon connector J1 on
the Limit/Alarm PCB Assembly. Depress both ears on the plug
housing and gently pull out the connector.
With an Ohmmeter, measure the resistance between TB1-4 (Orange
wire) and TB1-6 (Red wire).
The proper heater resistance is 32 ohms. If heater resistance is correct,
then measure between one heater lead (RED or ORANGE) and
incubator ground, it must be infinity (Open). If the heater resistance
check indicates an open circuit, it may or may not be open. In series
with the heater is a thermal overload switch. It might be that this
thermal overload is open and not the heater. To check the heater and
thermal switch directly, the shelfs of the incubator and the back wall
cover must be removed. Unplug heater and measure its' resistance. If
the resistance is correct, check resistance between heater terminal and
the heater sheath. It must be an open circuit. If the heater is good,
then check the thermal overload switch. At room temperature it should
be closed (0 ohms). This switch should only open at 80°C and then
close at 65°C. If the heater and thermal switch are good, then the
problem is directed towards the heater wires in the harness. If heater is
defective, contact Technical Services.
3. Malfunctioning Power Supply PCB assembly:
The Power Supply PCB Assembly has the triac (solid state AC voltage
switch) on it which supplies the power to heater. This triac is "told" to
operate, when need be, by the microprocessor.
Refrigerated Incubator
4-3
Thermo Scientific
Section 4
Service
Possible Solutions
