PCM-2 Manual.pdf - Voss Associates

tones, which emanate from the perforated section of the ceiling, are produced only
when the hand probe is removed from its holder on the side of the instrument.
Theory Of Operation
Clicker Board
Configuration
The modified Modular Detector Board (SP28B) is connected to the PCM-2
Clicker Board by the cable YPl1534522. The SP28B provides unregulated 10-12
Vdc power and ground to the PCM-2 Clicker Board. The signal which drives the
clicker circuit, provided by the MDB, is fed to the input of integrated circuit AI.
A1 provides pulses of constant width and timing, regardless of the duration or
spacing of its inputs. These are applied to the transistors Ql and Q2. The
outputs of Ql and Q2 are connected to the primary side of the transformer Tl.
The two pulses generated by Al act in a push-pull fashion to increase the voltage
swing across the primary side of the transformer. The transformer steps up this
voltage and then applies the voltage across the speakers SKI and SK2. The
volume of the speakers outputs are adjusted by potentiometer R4.
Due to component parts obsolesence since its initial production, the original
clicker board assembly has been redesigned. PCM-2's of serial numbers 101
through 171, if equipped with the Hand Probe Option, are furnished with the
original clicker PCBA (YPlI532000). PCM-2 units with serial numbers 172 and
subsequent are equipped with the revised clicker PCBA (YP1l585000). The
original clicker board can be easily distinguished from the revised counterpart by
its speaker arrangement. Whereas the original board included two (2) piezo
sounders and a transformer, the new revised board has no transformer and uses
only one speaker, mounted face-down on the board.
17-2
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