Advanced Instruments 3900, Руководство по обслуживанию

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3900 Circuit Description
The 3900 is comprised of the following
functional blocks:
Power Supply
The power supply is a + 12VDC, 350 watt
single output supply. This supply will accept
an input between 100-250 VAC without any
input configuration changes (auto switching).
For 100-130 input voltage at 50-60 Hz, use 5
AMP time delay fuses; for 200-250 at 50-60
Hz, use 2.5 AMP time delay fuses. The power
supply provides 12VDC to the main control
board, the motor control board, the cooling
fans (3), all thermoelectrics (5), the solenoids,
the stepper motors, and the cooling pump.
5VDC is supplied to the main control board
through a +5Volt voltage regulator (LT1003).
Other onboard circuits are used to provide all
other required voltages (i.e., ±12VDC,
±15VDC, ±5VDC).
NOTE The internal printer may be powered
by +5VDC (red/orange wire) or
+12VDC (violet wire). Consult
system schematics for proper service.
Sample Cooling Assembly
The sample probe thermistor measures the
temperature of the sample. The thermo-
electrics (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, the stir/freeze wire “buzzes”,
causing the sample to freeze.
4C3600 Main Board Description
General: The microprocessor is an 8-bit
63A03R (a member of the 6800 family of
microprocessors). The microprocessor runs at
approximately 1 MHz and has an address
space of 64 Kbytes. The microprocessor runs
the software stored in the EPROM and uses
the battery-backed-up 8 Kbyte static RAM to
store information.
A/D Converters: Two dual-slope A/D
converters using programmable timer modules
provide interface from the sample and block
probes to the microprocessor. The A/D
converters use a reference voltage of 6.25
VDC and provide 15 bits (1/4 ohm) of
resolution.
Sample Cooling Interface: The thermo-
electrics are interfaced to a programmable
timer module through discrete logic. The
programmable timer module interfaces
directly to the microprocessor. The stir/freeze
wire driver is interfaced to the D/A converter
through discrete logic. The D/A converter
uses a 60 Hz 0-5 volt reference from a
programmable timer module through discrete
logic. The D/A converter interfaces directly to
the microprocessor. The power transistors,
mounted on the heat sink on the rear of the
instrument base, control the thermoelectrics
and the stir/freeze coil.
Keypad Interface: A peripheral interface
adapter is used to interface the keypad to the
microprocessor. A 3- to 8-line decoder is used
to pulse the different columns of the keypad to
check for key presses. The microprocessor
controls the keypad LEDs.
Display and Printer Interface: A peripheral
interface adapter is used to interface both the
display and the printer to the microprocessor.
Supervisor/Operator Keyswitch Interface:
A peripheral interface adapter is used to
interface the supervisor/operator keyswitch to
the microprocessor.
Head Transition Board Description
The stir/freeze solenoid and the sample probe
are connected to the head transition board,
which allows easy replacement.
16 The Advanced ® Model 3900 Service Manual