Philips PM3208 Service Manual page 28

4.5 POWER SUPPLY
Input to the power supply is the mains-voltage; outputs are 6,3 V (AC) to the CRT and 4
DC voltages: -12 V, +5 V, +12 V and +160 V. The power supply consists of a
line-transformer, rectifiers and stabilising circuits.
The function of the line-transformer is:
- Providing a galvanic isolation between the mains-voltage and the electronic circuitry
in the oscilloscope.
- Adaptation to the right mains-voltage by means of different primary windings.
— Transforming the mains-voltage into the low voltages needed by the instrument.
The rectifiers convert the AC voltages from the line-transformer into DC
voltages. The output from D1002 at C1012 is about 190 V. The output from
D1001 is about +18 V at C1001 and —18 V at C1010.
Stabilisation is obtained by series-pass transistors Q1001-1002-1003-1004 which are
controlled by the operational amplifiers 1C1001 and 1002. The reference voltage to the
+12 V is about +6,2 V from diodes D1004 and D1005. Adjustment of the +12 V is done
by means of potmeter VR1006. As reference voltage to the -12 V, +5 V and +160 V
stabilisers, the +12 V is used. So, VR1006 will control all voltages and only one adjusting
element is needed.
4.5 POWER SUPPLY