Maintenance— Type M
Substituting an M or CA Unit is suggested because either
of these units aids in isolating such troubles as loss of sync
or improper chopped-mode blanking to either the oscillo
scope or the plug-in unit.
2. Visual Operation Check
A good procedure to follow when the trouble has been
isolated to the M Unit is to make a careful visual check
of the unit as described earlier.
If no trouble is visible, apply an input signal to all four
channels and observe the crt for proper waveshapes. Oper
ate the front-panel controls to see what affect they have
on the waveforms. The normal or abnormal operation of
each control will indicate the type of trouble that exists.
Once the symptoms can be observed, the faulty circuit
containing the trouble can
u s u a l l y
be isolated more readily.
Troubleshooting Procedures
This portion of the manual contains a suggested trouble
shooting technique, hints, and symptoms. The symptoms
contain troubleshooting procedures and probable causes
of the symptom.
Troubleshooting Technique.
When circuit troubleshoot
ing, a satisfactory technique is as follows:
(a) First, signal trace by using a calibrated oscilloscope
of proper bandwidth to assure accurate displays and
measurements. For example, when signal tracing through
the Channel Switching Circuit to locate the cause of im
proper electronic switching of channels, use a test oscillo
scope having calibrated time base settings and a band
width of 5 megacycles or more. Consider the loading
effect, if any, of the probe, and be certain the probe is
properly compensated.
(b) When an improper waveform is isolated to a stage,
substitute for the tube or transistor (whichever is employed}
in the defective stage. If this does not restore the proper
waveform, proceed to check the diodes (if used in the
stage), check voltages and, if necessary, make resistance
checks until the exact cause of the trouble is found. Re
sistance checks in transistorized stages are easier to make
when the transistors are removed from their sockets. When
measuring resistances in circuits employing diodes, consider
the polarity of the meter leads.
(c) If you have replaced a defective component and sub
stituted for tubes or transistors, return the good tubes
or transistors to their sockets. Such a procedure, if followed,
results in less recalibration of the M Unit upon completion
of the servicing.
Troubleshooting Hints.
The following hints are included
to aid you in avoiding certain pitfalls, and to speed up
tube and diode selection. Transistors, if they meet manu
facturer’s specifications, do not require selection. If you
are substituting any of the tubes or diodes mentioned in
the hints when troubleshooting or calibrating the M Unit,
use the associated information to make selection easier.
CAUTION
Do not substitute tubes or Nuvistors when the M
Unit is operating, as this w ill open the filam ent
series circuit.
Some o f the regulated voltages
along the series circuit w ill rise, causing serious
damage to the unit.
(a) When replacing V5383, choose a tube that has good
dc balance between halves. To do this, connect a shorting
strap between test points 8 and 9 and note the amount of
deflection from the vertical-system electrical center. Choose
a tube which causes the trace to shift no more than 2 cm
from the electrical center.
(b) When replacing V5364 or V5374, choose a tube that is
closely dc balanced to the other. To do this, connect a
shorting strap between test points
6
and 7. Try to bring
the trace back to the screen by rotating the VERT. POS.
RANGE control. If the trace does not return, reverse the
tubes and try again. If reversing the tubes does make the
trace appear, try another tube or pair of tubes and re
peat the procedure. Remember that V5383 must have good
dc balance before you can select V5364 and/or V5374
for proper dc balance.
(c) Nuvistors require selection to find one that will give
the DC BAL. control range of adjustment. To select V5323,
monitor the voltage at pin 8 of V5323. Choose a Nuvistor
which produces a meter reading of 1.25 to 1.75 volts. Then,
refer to steps 7 and 8 in the Calibration section of the
manual to check the Nuvistor for excessive grid current
and microphonics.
(d) Diodes D5345, D5347, D5346, and D5348 should be
checked for matched pairs (D5345 and D5347; D5346 and
D5348). A matched pair will insure that the flat top por
tions of the chopped-mode four-trace waveform will be
as flat as possible. To match diodes, measure the forward
and reverse resistances of each replacement diode. Find
a pair that has similar resistance measurements.
Symptoms.
The symptoms that follow are those that
could happen when certain troubles occur. Since it is im
possible to list every kind of symptom that could happen,
those that are included here provide the basis or guide for
analyzing others not described.
Procedures for isolating “ trouble" to improperly adjusted
front-panel controls are not included. See the Operating
Instructions (Section 2) if you are in doubt about proper
control settings.
1. Loss o f A ll Traces
For the traces to be visible on the crt, the dc output
voltage at test points 10 and 11 must be essentially
equal— that is, within a fraction of a volt. As little as a
0.2-volt difference between these two points may position
the beam above or below the range of visibility.
The dc output voltages depend on the dc balance of the
Output Amplifier. Since the Output Amplifier is dc-coupled
throughout, a condition anywhere between input and output
that unbalances the output voltage more than 0.2 volt may
cause a loss of all traces.
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