B&K 1076, Инструкция по эксплуатации

Страница: 32 / 64

NOTE: For the boost indicator to light up, R.F. pulses must be
present on the plate of the horizontal output tube. This, in tum,
means that boost B+ must be present, for without this additional
voltage, any R.F. pulses produced will be too weak to light up the
boost indicator. This makes the boost indicator doubly valuable be­
cause it provides a positive indication of whether the circuit is or
is not operating.
3. If neither the boost indicator or the high voltage indicator light up,
when the horizontal plate driving pulse is applied to the transformer,
we proceed in the following manner:
With a voltmeter, check the DC voltage at the plate of the hori­
zontal output tube. We know that boost B+ is absent and this test
is designed to reveal if any B+ is reaching the tube. If zero voltage
is measured at this point, then either the voltage is being shorted out
by boost filter capacitors C-3 and C-4 or the linearity coil L-1 is
open. Short out the linearity coil and test the circuit again. If
everything returns to normal, the linearity coil is open. If no change
occurs we can presume that the coil is OK.
Check capacitors C-3 and C-4 for any short or leakages. It should
be noted here that a failure of the boost B+ voltage being applied to
transformer terminal C will cause very little horizontal output signal
because the output tube does not have enough plate voltage. This
is because the boost B+ voltage is providing the power for the plate
of the horizontal output stage.
Returning to the damper circuit, if B+ voltage only is measured
on the boost B+ line, it indicates that no high pulse voltage is being
rectified and added to the B+ to develop a boost B+ voltage. There
is another boost circuit defect which can cause this and that occurs
when capacitor C-7 (Fig. 16) is shorted. For this condition, the B+
voltage will be applied from the plate of the damper tube to the
cathode; there will be no rectification in the damper tube and hence
no boost B+ voltage. This possibility can be checked by removing
the damper tube from its socket and nothing whether the B+ voltage
is still being measured at the cathode terminal of the damper tube
socket. If the answer is yes, C-7 is shorted and should be replaced.
However, if no voltage is present at the cathode of the damper tube
with the tube out of its socket, then C-7 is not shorted and the
damper tube can be returned to its socket.
The role played by the two special indicator lamps provided with
the TV Analyst demonstrates how useful they are in assisting the
technician isolate a defect in the horizontal output circuit. Once
their use becomes understood, they will be found to save many hours
of service work.
4. We shall now demonstrate how to locate quickly a defect in the
horizontal output system consisting of the transformer itself, the
horizontal yoke or any of the associated components attached to
these units. To check the horizontal yoke, it is only necessary to
disconnect the yoke from the circuit so that any shorting effect a
defective yoke might have on the rest of the circuit is removed. If
now, with the plate drive signal applied to the horizontal output
transformer, the boost indicator lights up as well as the hi voltage
indicator showing that high voltage is being produced, then the
defect in the set has been isolated to a shorted yoke. As a matter of
fact, a vertical white line will appear on the screen of the TV receiver
being tested, if the high voltage rectifier has been replaced in its
socket. However, if the yoke is not the defective component, there
will be no change in indications at this time.
30