Group 4 Functions - Polaroid 8035 Repair Manual

8K Series ProPalette Repair Manual Theory of Operation

Group 4 Functions

Filter Wheel Stepper Motor Control, J5 & J6
Two high-voltage, medium current dual peripheral drivers (75477) generate
PHASE1/PHASE2 and PHASE3/PHASE4 which turn on and off current in four stepper
motor windings. One side of each stepper motor winding is tied to +15Vdc and the other
side attaches to the low-side drivers (PHASEX). PHASE1 and PHASE 2 should always
be the complement of each other.
The same relationship applies to PHASE3 and PHASE4. Three 82C55 output bits control
the peripheral drivers. INTLED provides current for an LED photo-interrupter which
outputs a logic signal, FWSENSE, to indicate when a filter wheel slot is front of the
sensor.
Camera Back Interface Circuit, J13
The camera back interface is made up of one 74VHC244 8-bit buffer, one 74HC273 8-bit
latch, one 74HCT257 quad 2-to-1 mux, one LM311 comparator, two 75477 medium
current low-side drivers, one 2SA1314 PNP power transistor, one 754410 (or L293D)
dual half H-bridge and one LM317 linear voltage converter. The 8-bit buffer serves as an
input port for signals output from the camera back. DX code bits are selected for reading
via the 2-to-1 mux.
Both the 8-bit buffer and the 8-bit latch sit on the V53 buffered data bus, VBD7-0. The 8-
bit latch controls the camera shutter and film motor via control outputs fed to the 2 low-
side drivers, the dual half H-bridge and an open-collector driver connected to the base of
the PNP power transistor. The remaining 8-bit latch bits serve as the select bit for the 2-
to-1 mux and the perforation sensor LED On/Off control. The comparator translates the
perforation signal from the camera to a valid logic level. The voltage converter steps
15Vdc down to 6.4Vdc to supply the half H-bridge output driver.
LCD/Keypad Module Interface, J12
This interface consists of one 8-bit 82C55 port for LCD module data bus lines, four more
82C55 outputs for LCD module and backlight control, four 82C55 inputs for reading
keypad keys, one 2SA1314 PNP power transistor for driving the LCD backlight and 1/2 a
74HC20 4-input NAND gate for generating a key interrupt to the V53.
Analog Board Data and Control I/O, J18
The Digital Board outputs a number of data and control signals which connect to devices
on the Analog Board.
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