The EICO Model 369 TV/FM Sweep & Post-Injection Marker
Generator provides the greatest dependability, accuracy, and
speed for service and factory alignment of color and
black-and-white tv receivers and fm receivers.
With the EICO 369, circuit response is notaffected by
markers and markers are notaffected by circuit response. The
EICO 369 feeds only the required sweep signal to the input
of the circuit being aligned or tested. At the output end of
the circuit, a demodulator cable picks off the signal, and
feeds the demodulated signal to a mixer stage inside the
generator where the markers are added. Then this combined
signal is fed to the oscilloscope. This means that circuitry
under test of alignment is not affected by the marker
signal, and that traps in the circuitry will not reduce or
eliminate the marker.
The EICO 369 has a controllable inductor sweep circuit. This
type of purely electronic sweep circuit has no mechanical
parts to wear and give trouble later. The sweep generator is
independent of the marker generator. It has five ranges:
3-7. 5mc; 6-16mc; 16-42mc; 36-95mc and 75-220mc. All five
ranges are fundamentals and tuning to the desired center
frequency is simplified by a 6:1 vernier dial and a 350°
scale. Output impedance is 50 ohms. Retrace blanking is
obtained by both direct grid cut-off and indirect B+ cut-off
(via the AGC chain) of the oscillator with a blanking tube
that conducts during the negative excursion of the 60 cps
sine sweep. A three-stage AGC circuit keeps the level of the
swept signal constant over its entire frequency range, even
when the widest sweep width of 20mc is being used. A phasing
control at the rear of the EICO 369 adjusts permanently the
horizontal sweep signal fed to the 'scope.
The marker generator in the EICO 369 has 4 ranges covering 2
- 225mc. The highest range, 60 - 225mc, is the third
harmonic of the next lower range. All other ranges are
fundamentals. Frequency setting is simplified by a 6:1
vernier dial and a 350° scale. For a rapid check of marker
generator alignment, a 4.5mc crystal is supplied with each
generator. When plugged into a front panel socket it
automatically turns on a fixed frequency marker oscillator.
The 4. 5mc signal produced by this oscillator is mixed with
the variable frequency marker. The 4.5mc crystal is used
also for alignment of sound circuitry in tv receivers.
The demodulated wave form with post-injected marker is fed
to the vertical input of the 'scope, and the horizontal
sweep to the horizontal input of the 'scope, through a
single, shielded, two-conductor cable. Separate level
controls for trace size and marker size on the front panel
can be used independently.
1. Entirely electronic sweep circuit (no moving parts, hum,
or vibration) using controllable inductor, in which the
oscillator coil inductance depends on the controlled
excitation current in the primary windings of the unit. The
controlled inductor provides a large and smoothly variable
sweep width, and the sweep obtained is extremely linear and
stable. The availability of a large sweep width renders
operation of the instrument non-critical, since the
band-pass region is easily located on the 'scope trace even
when the tv set or generator are considerably off frequency.
Once the band-pass waveform is located, it is only a matter
of adjusting the sweep generator center frequency and the
sweep width as required for the most satisfactory display.
2„ Extremely flat sweep signal provided by the three-stage
AGC circuit which automatically adjusts the oscillator for
maximum output on each band with minimum amplitude
variations. High output on all five bands permits "cold"
alignment of all tuned circuits and filters.