Zenith Y504B - Page 14

B. On chassis 18YT20, 20YT20, 26YT20 and 26YT21
connect the scope to the base of the last FM IF
transistor Test Point (G). The common scope termi 
nal should be connected to chassis.
On chassis 23YT124 the scope should be connected
to terminal #5 of T4 the 4th I.F. transformer.
A detector probe is required. If your oscilloscope is
not equipped with this probe, it can easily be con 
structed. For best results, this probe should be
shielded.
Simplified Circuit Diagram of
Detector Probe.
AM ALIGNMENT
C. A V.T.V.M. on low AC scale connected across the
speaker voice coil output terminals (either left or
right channel), will be satisfactory for all AM, IF
and RF adjustments.
RF AND IF ALIGNMENT CHASSIS 6YT01
Alignment of these chassis will, in most cases be un 
necessary unless an IF or RF transformer is replaced
or the adjustments have been tampered with.
FM Ratio Detector Alignment: When the secondary of
the Ratio Detector is aligned use sufficient signal in 
put to get a good positive and negative indication be 
fore setting the slug for zero reading. A center zero
indicating meter is recommended for this adjustment,
but is not absolutely necessary. Reversing the leads
of a non-zero center meter, or observing closely when
the meter starts to go to the left (negative) of zero will
give the same results.
FM IF Alignment: Because of the wide band pass, it is
desirable to use an FM signal generator and a cathode
ray oscilloscope.
Correct alignment can only be made by following this
procedure:
A vacuum tube voltmeter with an isolation resistor of
2, 000,000 ohms in series with the hot lead will serve
for FM adjustments. This lead should be shielded.
The signal generator output should be kept just high
enough to get an indication on the meter.
14
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