Zenith Y504B - Page 20

67 KC Trap Adjustment injected at the output of the ratio detector. To reduce
possible extraneous signals coming through the ratio
1. Connect the stereo generator RF leads to the G detector, short the ratio detector primary with a jump-
and F FM antenna terminals and set the pilot e r lead. The wave forms and their magnitudes may
carrier control to zero. vary slightly from chassis to chassis, however, they
2. Move L + R and L - R switches to OFF position. are quite indietive of what will be seen when signal
3. Move 67KC generator switch from OFF position up tracing the multiplex circuitry.
to 67KC.
4. Connect the V.T.V.M. (AC scale) and/or scope 67KC Signal Tracinq
to terminal #5 Test Point “ M ” of T10 19KC am 
plifier transformer, and chassis ground. 1. Turn generator pilot carrier amplitude control to
5. Adjust 67KC trap for minimum output. zero.
6. Move 67KC generator switch to OFF position. 2. Move L+R and L-R switches to OFF position.
3. Move 67KC generator switch from OFF position
19KC Sub Carrier Amplifier, Doubler and Mute U p to 67KC. Sequentially connect an oscilloscope
Adjustments to the input and output of the 67KC trap. The
67KC signal at the output of the trap if it is prop-
1. Turn generator pilot carrier amplitude control to erly nulled, will be much smaller than at the in-
10% position. put. The voltage ratio should be approximately 20
2. Connect the V.T.V.M. (DC scale) and/or scope to to 1 input to output.
the junction of the two frequency doubling diodes
and chassis.
3. Place the stereo-monaural switch in stereo posi 
tion and short Test Point #T to GND, 19KC Signal Tracing
4. Adjust T10 19KC amplifier transformer and Til
doubler transformer for maximum output. Simul- 1. Move the 67KC generator switch to OFF.
taneously adjust the mute control so the voltage 2. Rotate the generator 19KC pilot carrier amplitude
at the junction of the two frequency doubling control to 10% position.
diodes never exceeds -.2 volt during this opera- 3. Sequentially connect your scope to the base of
tion. The voltage must be kept at this minimum composite amplifier, base of 19KC amplifier and
for proper alignment. collector of 19KC amplifier. The amplitude of the
5. Remove GND from Test Point #T. 19KC signal should greatly increase as you pro-
6. Turn generator pilot carrier amplitude control to cOed along the 19KC chain.
5% position.
7. Slowly rotate the mute control to a point where
the stereo indicator lights up. Doubler 0|)d Subcotrier Si g na | Tracing
To determine if the doubler is functioning, place
Separation Adjustments your scope at the junction of the two diodes and you
will see 38KC DC pulses. Placing the scope at the
1. Place stereo monaural switch in Stereo position. collector of the subcarrier amplifier, you should see a
2. Turn generator pilot carrier amplitude control to 38KC sine wave which will indicate that the sub-
10% position. carrier amplifier and associated ringing circuitry is
3. Moye L-R and L+R generator switches from OFF functioning properly.
position up to L-R and L+R positions.
4. Connect a V.T.V.M. (AC scale) and/or scope to
the L audio output, after the 38KC filter. e
5. Adjust T12 38KC detector transformer for maxi- Multiplex Detector Signal Tracing
mum voltage at L output. The magnitude of this , . , .
signal should be much greater than that at the R J- Leave the 19KC amplitude control at 10%.
output. The voltage at the L output should be 2. Move the L - R generator switch from OFF position
approximately 10 times or greater than at the R position. You should see equal amplitude
1000 cycle sine waves at both L and R outputs.
p ’ 3. Move the L+R switch from OFF up to L+R and
look at the L audio output, and measure the mag 
nitude of the 1000 cycle sine wave. If the multi-
TROUBLE-SHOOTING plex detector and preceeding circuitry are aligned
properly, the magnitude of the wave form at L
Should a problem arise in aligning the FM multiplex should be greater than at R.
portion of the receiver and the technician does not
know whether the difficulty lies in the RF, IF, lim- If all the waves are similar in form and magnitude to
iter and ratio detector portions of the receiver, or those indicated, then it can be assumed that the mul-
whether the difficulty lies in the multiplex portion, tiplex portion of the receiver is functioning properly
the multiplex generator can be used as an excellent and the problem lies ahead of this in the FM receiver,
signal tracing device to determine if the multiplex If any of the wave forms are missing at a latter point
section of the receiver is functioning properly. The but are apparent at a previous point, then something
composite output of the multiplex generator can be is amiss in the circuitry between the two test points.
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