Service manual

The HOP drives the frame output stage. As the HOP is 'cold' and the frame output stage
is 'hot', they must be galvanic isolated. This is done by means of an optocoupler. In the
MG-chassis, the HOP generates three signals needed for the frame output stage:
VDPOS, VDNEG and FRAME ROTATION. To avoid the costs of three optocouplers,
the frame drive pulse and rotation DC-voltage are added together and then fed to
optocoupler TS7610.
This is done as follows:
The positive frame output signal of the HOP (pin 1 of HOP, diagram B4) is extended for
16.5 lines and inverted via a mono-stable multivibrator (TS7311, TS7309 and TS7310,
diagram B4). This signal is called FRAMEDRIVE+. The output signal of pin 25 of the
HOP (rotation-information) is superimposed via TS7312 on this signal. The
FRAMEDRIVE+ and is fed to optocoupler 7610 (diagram A4). So this signal contains
info for both the frame deflection and the frame rotation (if present).
The circuit around IC7440 will amplify this signal and the output current will flow through
the rotation coil. The vertical pulses on this signal are filtered by C2445 to ensure that
only a DC-voltage will be supplied to the rotation coil.
The output voltage of the rotation circuit is between -8 and +8 V.
Figure: Frame deflection