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Drive jack to the plate lead connection on the horizontal output
transformer. Be sure the hi voltage indicator lamp is connected to
the plate cap lead going to the hi voltage rectifier and that this lead
is removed from the plate cap of the tube. Apply power to the re
ceiver and observe the B+ boost indicator lamp on the front of the
TV Analyst and the hi voltage indicator.
If both the B+ boost indicator and the hi voltage indicator lamps
come on, they indicate the presence of boost voltage in the flyback
system and hi level R.F. pulses in the hi voltage lead. Both of these
indications tell us that the flyback system is now operating properly.
The trouble must be in �ither the high voltage rectifier circuit or the
output tube circuit. To eliminate the hi voltage circuit, reconnect the
plate cap of the hi voltage rectifier tube, apply power to the receiver,
and again observe the boost indicator and the hi voltage indicator.
If both are lit this indicates that the high voltage rectifier circuit is
O.K. We must still check whether the high voltage dropping re
sistor R-4 is open, preventing the high voltage from getting to the
picture tube. If R-4 is O.K., then this proves conclusively that the
trouble must be in the horizontal output tube circuit. It could be
the screen resistor R-1, or by pass condenser C-1, or the cathode bias
resistor R-3. (See Fig. 16)
,r@
H.V.INDICATOR
FROM
C-2
HORIZ� t-----t-t
osc.
R-2
R-3
R-1
C-7
½C-3
Figure 16--A horizontal output section using an isolation type of output transformer
Screen voltage is applied to the horizontal output tube through the
screen dropping resistor R-1. There is also a bypass capacitor C-1
between the screen grid and ground. If resistor R-1 increases in value,
the screen voltage will decrease, there will be less drive to the hori
zontal output transformer, and the picture width will decrease. If
R-1 opens up, there will be no drive and no high voltage. Generally,
if R-1 is open it will be found that capacitor C-1 has shorted and
the excessive current drain has caused R-1 to burn out. In this case,
both C-1 and R-1 should be replaced. As a matter of prudence,
whenever R-1 has been found to increase in value substantially, it is
good practice to change capacitor C-1 because it frequently 'is the
cause of such resistance change.
In the grid circuit of the horizontal output stage, grid leak resistor
R-2 and coupling capacitor C-2 bring the signal to the horizontal
28
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Содержание 1076
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