Electronic Circuit Functions; Main Pc Board - Polaroid Miniportrait 455 Repair Manual

Electronic Circuit Functions

The electronic circuits of the Model 455 Miniportrait Camera are contained on four PC
Boards:
• Main PC Board ("Body Circuit"), inside the Camera Body;
• Two Electronic Flash PC Boards, inside the Flash unit;
• Sonar PC Board, on the underside of the Camera Body, inside the Bottom Cover.
Although the Model 455 circuits employ the same operating principles as Model 403/203
circuits, there are some unique component/operating differences in the 455. These
differences are highlighted by boldface type in the text below (Ex.: FET Q8 is turned
on).
Main PC Board (Figure 2-10)
Note: Text in boldface type denotes a difference between Model 455 & 403.
This circuit controls the Shutter charging motor and release magnet, the electronic flash
firing, and supplies power to the sonar ranging circuit. The circuit operates as follows:
1. When the Power Switch and S1 section of the shutter button switch ("SR Contact" on
the schematic) are closed, Q1 is turned on, powering the Sonar Ranging circuit.
2. Depressing the shutter button further closes section S2, supplying power to R5, D4
and C1, turning on Q2 and charging C2 through R8. C2 then turns on Q5 and Q6
through R13, energizing the release magnet to release (unlatch) the shutter).
3. As the shutter is released, S3 closes, turning on Q4 and starting the motor. As the
motor runs, S4 closes and S3 opens. After the shutter has been charged, S4 opens,
Q4 is turned off and FET Q8 is turned on, stopping the motor rapidly. With the
Camera Power Switch and the Flash Unit Switch ON, pressing the SR contact (shutter
button) will not release the shutter unless the Flash unit is fully charged. It works in
this manner:
4. When the Flash Switch is turned ON, the Flash Unit outputs a Power Monitor signal
which turns on Q7. This turns on Q3, cutting off the base of Q2 and de-energizing the
release magnet circuit.
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