The Advanced
®
Model 3250/4250 Service Manual
24
The instrument is comprised of the following
functional blocks:
Power Supply
Serial Suffix A - C
The power entry assembly interfaces the AC
voltage presented to the instrument with the
transformer. The transformer provides 120
VAC to the power supply board and the head
motor. The power supply provides the power
to run the main printed circuit board (±12
VDC, ±5 VDC), the thermoelectrics (5 VDC),
the fan (12 VDC), the stir/freeze coil
(12 VDC), and the internal printer (5 VDC).
Note: The internal printer may be powered by
+5 VDC (red/orange wire) or +12
VDC (violet wire). Consult system
schematics for proper service.
Power Supply
Serial Suffix D and Higher
The power entry assembly interfaces the AC
voltage presented to the instrument with the
AC/DC switching power supply. The power
supply provides the power to run the main
printed circuit board set (±12 VDC, +5 VDC),
the thermoelectrics (5 VDC), the fan (12
VDC), the stir/freeze coil (12 VDC), the inter-
nal printer (12 VDC), and the motor and con-
trol circuits (+24 V).
Front End
The sample thermistor measures the tempera-
ture of the sample. The thermoelectrics
(whose duty cycle is controlled through the
block probe/thermistor) supercool the sample.
The stir/freeze wire constantly stirs the sample
to guarantee uniform cooling. When the
supercooled sample reaches a set temperature
(3000 mOsm for the low range and 4800
mOsm for the high range, by default, in the
3250, and 3000 mºC in the 4250), the
stir/freeze wire "buzzes" causing the sample
to freeze. During a test, the fan duty cycle
tracks the thermoelectrics duty cycle -10%. If
duty cycle drops below 20%, the fan is off. In
between tests, the fan runs as required to
maintain the software controlled target tem-
peratures.
325605 Control Board Set Description
General: The control board set is made up of
two printed circuit boards in a motherboard/
daughterboard configuration.
3250/4250 Circuit Description
Processor
Board
Serial Port
Applications
Board
Cooling
System
Power
Supply
Head Motor
Controls
PrinterKeypadDisplay
Barcode
Port
To Next Page
Loading...
Need help?
General
