117
AM/FM Stereo Tuner
After these preliminary tests have been successfully completed, a full alignment should be
done on the tuner as detailed in Section 7.
6.1
Troubleshooting
Some common types of troubles are listed below, a long with simple trouble-shooting procedures
that are often helpful in locating the source of difficulty.
5
6.1.1 Tuner Completely Inoperative
An inelegant, although effective approach to narrowing the scope of a troubleshooting project
involves a simple “disturbance” test. If a stage in the tuner is operating normally, a sound will
usually be heard in the output when the grid of an operating stage is touched by the metal part of a
voltmeter test lead. Start with the last stage in the tuner and work backward toward the RF input.
When the grid of each stage is contacted, a click or hum should be heard. Move from stage to
stage until no response can be heard when the grid of the stage is contacted. If a point is found
where no response is obtained, the defective stage has been identified and checking can be
concentrated there. Response all the way through the tuner but still with no signal reception may
be indicative of serious misalignment of either the IF stages or the tuning coils or capacitor.
Likewise, if response can be obtained throughout the receiver but no reception is possible, the
oscillator may be badly off frequency or not functioning.
If a signal generator is available, the same procedure can be observed by injecting an AM-
modulated signal at the points indicated previously at the appropriate frequency. For the FM
V59,
12AU7
1
125 V
2
15 V
3
23 V
4
6.3 V ac
Measured with respect to pin #9 (heater)
5
6.3 V ac
Measured with respect to pin #9 (heater)
6
125 V
7
15 V
8
25 V
9
6.3 V ac
Measured with respect to pin #4 of #5 (heater)
5. This section was adapted from: Heathkit: “Assembly and Operation of the Heathkit Broadcast Tuner Model BC-1A,” the Heath
Company, Benton Harbor, MI.
Table 6.3
Typical Operating Voltages (+dc unless noted)
Summary of Contents for AM/FM Stereo Tuner 2012
Page 1: ...WhitakerAudio AM FM StereoTuner User and Assembly Manual...
Page 11: ...11 AM FM Stereo Tuner Figure 1 1 Schematic diagram of the AM tuner section...
Page 17: ...17 AM FM Stereo Tuner Figure 1 2 Schematic diagram of the FM tuner section...
Page 34: ...34 WhitakerAudio Figure 3 1 Component layout for the AM tuner PWB...
Page 36: ...36 WhitakerAudio Figure 3 3 Component layout for the FM tuner PWB...
Page 69: ...69 AM FM Stereo Tuner Set the FM tuner board aside it will be used later b...
Page 101: ...101 AM FM Stereo Tuner Figure 5 11 Chassis view of the AM FM Stereo Tuner...
Page 159: ...159 AM FM Stereo Tuner...
Page 160: ...WhitakerAudio AM FM StereoTuner...
