Maintenance— Type M
One cause of dc imbalance is improper adjustment of
the VERT. POS. RANGE control. Check the adjustment by
performing step 3 in the Calibration procedure. Another
cause could be imbalance due to a defective tube. Substi
tute for V5364, V5374, and V5383. Repeat step 3 in the
Calibration procedure.
Other causes of imbalance are defective resistors, shorted
or leaky capacitors, or open peaking coils. To isolate the
cause of imbalance, a step-by-step procedure must be
employed.
The procedure for isolating the cause of imbalance is
accomplished by shorting together corresponding points on
opposite sides of the Output Amplifier, starting at the out
put and working back toward the input. For example, set
the oscilloscope time-base and triggering controls to obtain
a 0.1-millisec/cm free-running trace. Short test points 10
and 11 together. The voltages at these points will now be
equal and the trace will appear at or near the center of
the crt. The position of the trace is the vertical-system
electrical center. From this point, the shorting strap can
be moved back in successive steps to test points 8 and 9,
and
6
and 7.
In following this procedure, a point will be reached
where the trace cannot be made to appear when corres
ponding sides of the Output Amplifier are shorted to
gether. When this occurs, the defect has been isolated
to the stage in which these points are located. For ex
ample, if the trace appears when test points 8 and 9 are
shorted together but does not appear when points
6
and 7
are shorted together, an open peaking coil L5363 or L5373
is a possible cause of trouble.
There is a possibility that the loss of all traces may be
due to a defective heater circuit. This condition can be
determined by observing the tubes in the M Unit for heater
glow. If no glow is observed, it will most likely be due
to an open heater in one of the tubes. Other possibilities
are shorted capacitors C5390, C5392, C5394 and C5395.
2. Loss o f Trace, One Channel
During multi-trace operation, if the trace for one channel
cannot be positioned on the crt, it would indicate a dc
imbalance in the Input Amplifier of that channel. Since
the Input Amplifier is dc-coupled, a similar procedure to
that given for the previous symptom would apply here.
In addition, a good procedure to follow is to compare your
results with the other Input Amplifier channels. Transistors
and Nuvistors in a channel that is operating normally can
be interchanged with those in the inoperative channel as
part of the procedure given in steps b and c.
a. Short together test points 1 and 3. If the trace does
not appear, the trouble lies between the collectors
of Q5324/Q5334 and the control grids of V5364/
V5374. Check (for open diode) D5345, D5346, D5347,
or D5348.
b. If trace appears when shorting test points 1 and 3
together, short together the bases of Q5324 and
Q5334. If trace does not appear, check for trouble
in the Paraphase Amplifier stage Q5324 and Q5334,
including the POSITION control circuitry.
c. If trace appears when shorting the bases of the tran
sistors together but disappears when jumper is re
moved, check for trouble in the base circuits of Q5324
and Q5334.
3. In a b ility to Position Trace, One Channel
If the trace for one of the channels cannot be vertically
positioned with the appropriate POSITION control, some
defect that is rendering this control inoperative is indicated.
For example, check for an open POSITION control R5342.
4. Abnorm al Positioning Range, One Channel
If the POSITION control for one channel must be set to
an abnormal setting to position the trace on the screen,
check for a shorted diode D5345 or D5347.
5. Interacting POSITION Control, M ulti-trace Operation
If the POSITION control for one channel affects the
positioning of other channels, check for a shorted diode
D5346 or D5348.
Another symptom caused by the same trouble is that the
POSITION controls require a setting approximately 90°
from midrange to position the traces on the screen.
6. Loss o f Two Traces, A lternate Mode
During
four-trace operation
when
the ALTERNATE/
CHOPPED switch is set to ALTERNATE, if only two ab
normally wide traces appear, check the CHOPPED posi
tion. If four traces are displayed and they are also ab
normally wide, set the oscilloscope sweep rate so that you
can determine the chopping rate. If it is approximately
3 me, check for an open diode D6360.
7. Loss o f Three Traces, Alternate or Chopped Mode
During four-channel operation, if only one trace appears
for either setting of the ALTERNATE/CHOPPED switch, this
would indicate trouble in the Ring Counter, Switching
B.O., or Chopped Mode Blanking Amplifier. The trouble
can be further isolated by proceeding as follows:
a. Observe waveforms at test point 17.
b. If waveforms are normal, check voltages at test points
12 to 17 in the Ring Counter. Troubleshoot the circuit
where an abnormal reading is found.
Substitute
for the transistors in the Ring Counter.
c. If test point 17 waveforms are abnormal, replace
Q6350 and Q6364. If this does not restore normal
operation, then check D6352 and D6360.
d. If substitution of transistors and diodes does not re
store normal operation, proceed with voltage checks
at test points 18 and 19 to determine if these circuits
contain the trouble. If further isolation of the trouble
is necessary, detailed voltage and resistance checks
will have to be made.
8. Loss o f Three Traces, Alternate Mode
If only one trace appears when the ALTERNATE/
CHOPPED switch is set to ALTERNATE during four-trace
4-6
®
