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(continued)
Thermo Scientific
6. Measure the voltage between U1-Pin 4 and U1-Pin 6. It should be
line voltage. 110 VAC to 120 VAC.
7. If it is not, most likely the Optoisolator is bad and the power
supply board will have to be replaced.
8. Measure the voltage TB1-4 (Orange wire) and TB1-6 (Red wire).
It should be approximately 0 VAC.
9. If it is not, then most likely the triac is bad, and the power supply
board should be replaced.
C) This next section will be to verify the heater command is correct from
the microprocessor, through the optoisolator, and through the Triac
when the incubator is requesting heat. The steps in this section must
be followed in succession.
1. Select a setpoint temperature at least 10° above what the actual
temperature is. The incubator should be requesting heat as
indicated by the "Heater On" indicator lamp on the front panel. It
should be on continuously, not flashing.
2. Measure the voltage at U1-Pin 2 with respect to TP2. It should be
no greater than 4 volts DC.
3. Measure the DC voltage across R4, since the incubator is
requesting heat, there should be current flowing through this
resistor, making the voltage drop equal to 3 volts ±0.5 volts.
4. If the last two steps are not as stated, then most likely the CPU
board is bad and should be replaced.
5. Switch voltmeter to "AC Volts" scale capable of reading 120 volts.
6. Measure the voltage between U1-Pin 4 and U1-Pin 6. It should be
less than 1 VAC.
7. If it is not, most likely the optoisolator is bad and the power
supply board should be replaced.
8. Measure the voltage between TB1-4 (Orange wire) and TB1-6
(Red wire). It should be line voltage. 110 VAC to 120 VAC.
9. If it is not, then most likely the triac is bad. The power supply
board should be replaced.
Section 4
Service
Refrigerated Incubator
4-5
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