B&K 1076, Инструкция по эксплуатации

Страница: 31 / 64

output stage from the horizontal oscillator. This coupling capacitor
is frequently the cause of much difficulty in the horizontal output
circuit. If C-2 becomes leaky or shorted, a positive voltage will be
applied to the control grid of the horizontal output stage ,from the
plate circuit of the oscillator. If the leakage resistance of C-2 is low
enough, this could load down the horizontal oscillator circuit suffi­
ciently to prevent any horizontal output or high voltage from being
developed.
It is interesting to note, that if C-2 is leaky, with a. fairly low re­
sistance, applying the grid driving pulse to the horizontal output
stage from the Analyst may not cause the high voltage to reappear
since the shorted coupling capacitor may load down the Analyst
circuit as well. To see if this is so, uncouple one side of C-2 and
reapply the grid drive. If ·the high voltage now appears, capacitor
C-2 should be changed.
2. If you find that injecting the signal from the TV Analyst at the plate
of the horizontal output tube
does not
restore high voltage, then the
trouble lies somewhere in the circuit
beyond
the horizontal output
stage. NOTE: This is a
conclusive
test and it due
entirely
to the
fact that the TV Analyst can take the place of the horizontal output
amplifier.
The procedure to check out the output circuit with the instrument
is as follows:
The cap lead is lifted from the top of the horizontal output tube;
also the cap lead connecting to the high voltage rectifier is removed
from its tube. As an added precaution, the high voltage rectifier tube
is removed from its socket. The TV Analyst is then set to deliver a
horizontal plate driving pulse. The lead from the Plate Drive terminal
is connected to the cap lead that ordinarily goes to the horizontal
output amplifier. Next, the B & K high voltage indicator light is
attached directly to the
insulated
wire leading to the cap that con­
nects to the high voltage rectifier. (See Fig. 15). The instrument
and the television receiver are both turned on.
If the boost indicator light on the panel of the TV Analyst lights up,
as well as the high voltage indicator, high voltage is being developed,
boost B+ is present, and R.F. is being produced in the circuit. This
is the condition that would generally be obtained when the set is
working normally. In the present instance, the set is presumed to
be defective; therefore, if such an indication is obtained, but there is
no high voltage on the picture tube as indicated by lack of raster,
it is possible that capacitor C-6 in Fig. 16 may be shorted, or the
high voltage cable is not connected to the CRT. (We are assuming
that all the tubes in the circuit including the picture tube have
previously been checked before any testing with the instrument
is begun.)
Another possible cause of no raster when the hi voltage indicator
lights up is an open in the current limiting resistor R-4, preventing
any high voltage from appearing on the picture tube. Each of these
components can be checked individually to determine which is
defective.
If the boost indicator lights up when the horizontal plate drive is
applied to the transformer but the hi voltage indicator
does not
and
there is no high voltage, then we have a definite indication that the
trouble is in the transformer winding from point A to point B
in Fig. 16.
29