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11
The collectors of the ring counter are connected to the
electronic switch.
As already mentioned in chapter V A, the relevant
channels can be switched on or off with a negative and
positive voltage respectively.
If a channel is not used (INV-OFF-NORMAL (SK4,
8, 12, 16 switch to position OFF), the transistor in the
ring counter corresponding to this channel is cut off by
connecting the base to the negative supply voltage via
a resistor (R702 or R704 or R707 or R709).
Moreover, the capacitor connected between the pre-
ceeding collector and the relevant base is switched over
to the base of the next functioning transistor.
The collector wave forms are shown in Fig. 4.
The collector wave forms with two channels switched
off are shown in Fig. 5.
The switching frequency in CHOPPED position is always
2 MHz, so that in this position a different channel is
displayed every 500 ns.
PEM 3529
Fig. 3. Collector wave forms during
Fig. 4. Collector wave forms
if
one
Fig. S. Collector wave forms
if
two
the switching
channel is switched
off
channels are switched
off
Checking and adjusting
A. GENERAL
The tolerances mentioned are factory tolerances; they
apply when the apparatus is readjusted completely.
They may differ from the data given in II.
With the aid of these data, it is possible to carry out all
the adjustments to four-trace unit PM 3344 and to
check the proper working of the plug-in unit.
For this, the unit should be inserted into the Y-plug-in
compartment of a correctly adjusted basic oscilloscope.
Some of the adjusting elements are on the right-hand
side of the unit and are not directly accessible.
When these elements should be adjusted, the unit
should be connected to the basic oscilloscope via the
rigid extension plug. (code number 5322 263 70009).
For a complete adjustment of the instrument the
sequence as described in this chapter is to be preferred.
Note: Only the input FET's must be paired and the
transistors TS108, 109, 208, 209 etc. selected on equal
Vbe. All other semiconductors can be ordinary pro-
duction ones.
B. DC BALANCE
This adjustment should be carried out when the unit
has obtained its operating temperature, i.e. 10 minutes
after switching-on.
Set the knobs of the basic oscilloscope to the following
positions:
TRIGG. MODE
(SK1) to AUT.
(SK2) to +
TRIGG. SOURCE
(SK3) to INT.
TIME/cm
(SK4) to .5 msec.
X-DEFLECTION
(SK7) to TIME BASE A or MAIN T.B.
1. Channel A (B, C, D)
R2 (R7, l 2, 17) (Fig. 1)
R135 (R235, 335, 435) (Fig. 6)
— Set INV-OFF-NORM. SK4 (SK 8, SK 12, SK 16) to
NORM.
— Set potentiometers DC BAL, R2 (R7, R12, R17) and
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