Zanussi 22ZT907 Service Manual page 33

ADJUSTMENT OF QUARTZ CONTROLLED FREQUENCY
A Method
The free running frequency of the oscillator is adjusted by means of
a capacitive trimmer C26T connected in series with the quartz.
The oscillator is free running when pin
directly connected to +12 V (jumper between TPl and TP2) and pin 7 is
connected to +12 V via a 5.6 M Ohm resistance (jumper between TP3 and
TP4).
Video signal (TP8) on oscillator is compared against sand-castle
pulse present on Pin 5 of SAA 5030 (TP 7).
Capacitive trimmer is adjusted so as to maintain ratio between the
two signals unchanged (i.e. find the position in which relative shift
between the two waves is less emphasized).
Remove again shortcircuiting jumper and 5.6 M Ohm resistance.
Oscillator free running frequency is encreased by means of this
resistance from approx. 0.5 kHz to over 6 MHz, this assuring that
signal quality detector provided in circuit SAA 5030 operates in the
best manner.
B Method
For capacitive trimmer adjustment it is also possible to use the same
teletext reproduction.
Once again it is necessary to connect the short circuiting jumper and
the 5.6 MHz resistance as described above.
By means of remote control the teletext decoder is switched to mixer
operation.
Page memory does not necessarily have to be occupied with a teletext
page, but it is possible to use randomly selected characters
contained in memory which are sufficient for adjustment by means of
reproduction on the screen.
Capacitive trimmer is adjusted so that characters occupy a fixed
position on the screen.
Remove once again the shortcircuiting jumper and the 5.6 MHz
resistance.
If, by means of capacitive trimmer adjustment, characters do not
reach a condition of rest, it is sufficient to adjust for minimum
character shift.
of SAA 5030 circuit is
1