The Advanced
®
Model 3250/4250 Service Manual
To determine if a faulty probe is causing the
problem:
1. Disconnect the probe from the main
board.
2. Place a 6 Kohm fixed resistor across pins
1 and 2.
3. If the resistance display changes to
approximately 6,000 ohms, replace the
probe.
If the resistance does not change, replace
the main control board or application
board.
If the resistance on both channels does not
increase, or if the temperature reads approxi-
mately ambient while a target temperature is
set, the situation indicates a problem with
either the cooling assembly or application
board.
To determine which component is faulty:
1. Remove the empty tube from the freezing
chamber.
2. Set the target temperature to -8.
3. Raise the head manually and place a ther-
mometer inside of the freezing chamber.
4. If the temperature inside the freezing
chamber drops to approximately -8ºC, the
cooling assembly is working, and the
application board needs to be replaced.
If the temperature remains at room tem-
perature, replace the cooling assembly.
Note: When the A/D channel is open, there is
a thirty-second delay in response to
any resistance change.
CAUTION: If the A/D test sample freezes,
allow it to thaw before attempt-
ing to remove the sample probe.
Sample Bin Setting
If you do not know the sample bin number, or
if you want to verify the sample bin number:
1. Turn on the instrument. If there is a
Supervisor/Operator keyswitch, turn it to
the Supervisor position (if required).
2. Press TEST. Press < or > to select
“Probe Bin Test”, and then press
START.
3. Place a sample of Probe Bin-Setting Fluid
into the freezing chamber.
4. At “[START] Ready?”, press START.
5. At the end of the test, record the sample
probe resistance and the bin number, and
then press STOP. The display will
change to “Probe Bin Test”.
To set the correct sample bin number, fol-
low steps 6-8.
If the current sample bin number matches
the number just recorded, press STOP
twice to exit the menu.
6. Press SETUP. The Supervisor/Operator
keyswitch must be in the Supervisor posi-
tion.
7. At “Select Setup Item”, press < or > to
select “Select Sample Bin #”, and then
press START.
8. If the current sample bin number is not
the same as the one recorded in step 5,
enter the correct number, press ENTER
twice, and then press STOP twice to exit
the menu. Recalibration will be required.
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