Philips PM3208 Service Manual page 19

3 BLOCK DIAGRAM DESCRIPTION
The circuit is located on printed circuit boards and is sub-divided into the following parts:
— vertical deflection
- horizontal deflection
— power supply
The blockdiagram of this instrument is given in figure 3.1. The subdivisions of the
diagram do not necessarily relate to the circuit areas of the printed circuit boards.
3.1 VERTICAL DEFLECTION
Channel A and Channel B are identical in operation with corresponding circuitry in each
channel. Input signals from the BNC input terminals are attenuated through the
ATTenuator network circuit. This block has two sections, the first attenuates by ratios of
1:1, 10:1, 100:1 and the second by ratios of 2:1, 5:1, 10:1.
The PRE-AMPLIFIER circuit converts the single-ended input signal from the attenuator
into a differential output signal. It includes compensating networks to obtain a good
input signal waveform and to adjust square wave response.
Input signals amplified in the PRE-AMPLIFIER are fed to the VERTICAL SWITCHING
circuit and to the TRIGGER AMPLIFIER circuit. The TRIGGER AMPLIFIER amplifies the
signal for the proper output signals to the TRIGGER SELECTOR ard to the HORIZONTAL
DEFLECTION unit.
The VERTICAL SWITCHING circuit consists of diode-gate and mode control logic. This
stage selects ch. A, ch. B, DUAL or ADD. The MODE CONTROL LOGIC is controlled by
the output of this diode-gate and conveys the selected signal to the VERTICAL OUTPUT
AMPLIFIER.
The vertical signal derived from the diode switching circuit passes the limiter circuit to
obtain an adequate level, and then is fed to the OUTPUT AMPLIFIER. The output
obtained is sufficiently amplified by the amplifier with a constant current load. This
amplifier is equipped with a booster for high frequency contents to obtain flat signal
response. The signal is then fed to the vertical deflection plates of the CRT.
3.1 VERTICAL DEFLECTION