or the DEMOD jack 0503) and either is
selected by the PROBES switch S512 and
the signal is then processed through Ql9, a
phase splitter, VERTICAL switch S515, Pat-
tern Output Amplifier Q20 and from there
through a 15,750 Hz filter to SCOPE VERT
INPUT jack J504. Connect an audio oscil-
lator to either the DIRECT or the DEMOD
jack and, with the PROBES switch in the
corresponding position, observe the oscillo-
scope ouput. The condition of the pattern
amplifiers can then be determined.
1.2.l.5 MARKER DETECTORS AND AMPLIFIERS
The 44 MHz Detector Ql5 and the 10.7 MHz
Detector Ql6 as well as marker amplifiers
Ql7 and Ql8 are energized at all times.
Outputs are generated by these circuits
when the proper input signals are furnished
from the FUNCTION switch or from stages
activated by other front panel switches,
such as the marker switches.
12.l.6
VIDEO IF/RF ATTENUATOR Q306
12.2
12.2.1
12.2.2
12.2.3
All Model 415 outputs are supplied to the
output jack through the attenuator stage.
The gain of this stage is controlled by AT-
TENUATOR control R515.
USE OF MAINTENANCE INFORMATION IN
TROUBLESHOOTING
An example of the use of the troubleshoot-
ing information furnished will be outlined.
Assume that there is no video output with
the FUNCTION switch in the VIDEO posi-
tion, but outputs at all other FUNCTION
switch positions are normal. Refer to Figure
4.1 (Repeated).
Check that marker operation is normal.
Because of the post injection marker sys-
tem, markers will be available if Marker
Amplifier Ql7 and Ql8, 44 MHz Detector
Ql5, 44 MHz Sweep Oscillator Q201 and
Buffer Amplifier Q202 and the Marker Os-
cillators Q2 through Q 11 are operating
properly.
If output is available in the IF position of
the FUNCTION switch and if the CHROMA
switch is effective in providing the proper
signal for circuit alignment, Pix Oscillator
Q402 is operating properly, but may not
have de applied in the VIDEO function.
Check the d-c switching to the stages out-
lined here.
Notice in Figure 4.1 that the combined out-
puts of the 44 MHz sweep oscillator and the
pix oscillator are supplied through the
FUNCTION switch to Low Pass Filter and
Video Sweep Amplifier Q401, and that the
output of Q401 is fed through Attenuator
Q306 to the output jack. Because this stage
is used only in the VIDEO function,
it
should be investigated. Access to this stage
is obtained by removing the bottom cover
of the Model 415. The parts layout diagram
of Figure 12.5 and the voltage chart of Table
12.3 can be used for reference. The sche-
matic can be used to check cabling and d-c
12.2.4
12.2.5
12.3
switching if required.
The above troubleshooting information is
condensed in the troubleshooting chart of
Table 12.l. Under the TROUBLE column
locate "No Video Sweep Output." Opposite
this under POSSIBLE CAUSES are listed
Q401 (Video Sweep Amp), Q402 (Pix Osc),
X401 (Pix Osc Crystal), D403 (Mixer diode),
Q201 (44 MHz Sweep Osc) and Q202 (44
MHz Buffer Amp). As explained previously,
normal outputs in other FUNCTION Switch
positions as well as evidence of Markers
in the VIDEO position of the FUNCTION
switch eliminate all suspected stages ex-
cept Q401 and diode D403.
The switching information of Table 12.2
summarizes in chart form the information
of the functional block diagrams. Only the
stages affected by the FUNCTION switch
are indicated. The left hand column lists
the FUNCTION switch positions in order,
and the headings across the top list the
stages affected by the FUNCTION switch.
For each position of the FUNCTION switch
the corresponding condition of each stage
is given.
REPLACEMENT OF DEFECTIVE
COMPONENTS
All components shown in the parts layout
drawings of Figure 12.2 and Figure 12.3 are
accessible from the component side of the
P.C. boards by lifting the cover of the Model
415. For component replacement access to
the underside of the P .C. boards is obtained
by removing the bottom cover of the unit.
This is done by removing the four corner
screws which retain the rubber feet on the
unit as well as the four remaining screws.
two toward the front of the unit and two
toward the rear of the unit. Removal of the
bottom cover is also necessary to provide
access to the Pix Oscillator board of Figure
12.5. Once the bottom cover is removed the
component side of the Pix Oscillator board
is accessible. For replacement of compo-
nents the underside of the Pix Oscillator
board is accessible by removing the three
P.C. board mounting screws which hold the
Pix Oscillator board in place. The board
can then he turned to allow access to the
underside.
Component replacement on the sweep os-
cillator board of Figure 12.4 is performed
as follows. Inscribe or pencil a line on the
tuner carriage to indicate the position of the
pointer which is attached to the carriage by
means of a sheet metal screw. Loosen the
screw which retains the pointer and remove
the pointer. Unsolder resistor R516 at point
K as indicated in Figure 12.4. Unsolder the
lead of C505 which connects to TP-203 on
the sweep oscillator board as indicated in
Figure 12.4. Remove the five mounting
screws which hold the sweep oscillator
board in place. Gently slide the oscillator
board with the tuner attached straight back
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