Assistant Service Manual
OPTIKON 2000
Code 121008S 6-17 Rev. D
Amplitude control section and Minimal Stress circuitry
Amplitude of sinusoidal signal applied to handpiece is proportional to the
direct voltage present at the central tap of primary winding of L1 transformer.
It is the output of switching regulator made up by U18,CR2,L2,C4.
This voltage, divided by R6,R7,R8, is applied to the NON INV pin of U7B
(lets call it Va) and compared with the reference voltage, set by the
microcontroller, present at the INV. pin (Vb).
Reference voltage Vb can be varied by the microprocessor by the means of
DAC U3. The information conveyed by micro to DAC U3 is determined by the
means of a patented electronic circuit named “Minimal Stress” (ESS module
in the schematics).
The U/S amplifier is stopped for 2ms 100 times per second: during the stop
period, the handpiece continues its oscillation because of mechanical inertia,
this oscillation excites the piezoelectric crystals, which generate a voltage
proportional to the amplitude of oscillation. This feedback voltage is
compared to the PRESET analog signal from the Control Board (which
represents the desired amplitude of oscillation set by the operator). The
result of this comparison is then used to set the voltage to the U/S amplifier
for the next cycle.
Phase-shift detector section
The sinusoidal voltage present on the handpiece, is squared and made TTL-
compatible by the U17 Zero-Crossing-Detector and sent to the PLD ( ZCR
signal).
It is then compared with signal CK40K coming from local oscillator U9, and
its phase-shift is measured. The phase-shift value is a 6-bit word ( Q0-Q5
signals of PLD) and it is sent to buffer-latch U15, where it is available for
reading by the microprocessor.
Handpiece acknowledgement
The microprocessor can determine if the handpiece is connected to the
console by reading U7A comparator output. When handpiece is cut-out, the
+ inlet of comparator is at high level. When handpiece is connected, the +
inlet goes to 0V since handpiece has an inside shunt to ground.
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