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I1AINTENANCE
PREVENTIVE I1AINTENANCE
The M6108A Monitor Amplifier is designed
for long, trouble-free service.
However,
as with all high quality electIonic equip-
ment, a regular program of inspection
should be followed.
These points should
be covered:
1.
Check the power amplifier supply
voHalOe at the collector of Q5 or Q7.
On the power transistors, such as the
2N1l83 and 2N3614, the collectoI is con-
nected to the case.
2.
Check the speaker bus voltage,
which appears at the GO.llec;tors, OT'
cases of Q6 and Q8.
3.
Remove dust which collects on the
printed board or in the housing, with a
soft brush.
It is recommended that when the ampli-
fier is first placed in operation, that
D.C. voltages be measured with the sane
vol tmeter that will be used for
~~t!_nten
a;J.c;e and troubleshooting, and tha-c these
readings be recorded on the amplifier
schematic.
The speaker bus a.'1.d B- vol
t-
ages should be r€coIied with an without
signal.
SERVICING
When servicing the amplifier, the follow-
ing points should be observed:
1.
The condition of the power supply
can be most readily cheeked by measuring
the D.C. voltage between the chassis and
the case of output transistor Q8.
(One
of the tW) power transistors mounted on
the end of the chassis).
This voltage
will be much higher or lower than nor-
mal if trouble is pIesent jn the power
amplifier.
2.
Voltages may be checked with Q5,
Q6, Q7 and Q8 removed, provided that the
speaker load is disconnected.
3.
Circuit resistances should be meas-
ured only after removing the associated
transistor or transistors, to prevent
damage due to ohm-meter battery voltage.
4-.
Do not remove or insert transistors
with the power on.
5.
Do not probe the pI inted boaId with
a metal probe with the power on.
6.
Circuit voltages are reversed from
standard vacuum tube practice, as is the
polarity of all electrolytic capacitors.
7"
The location of the positive end of'
each electI'olytic capacitor is indicated
by the white dot maIked on top of the
circuit board.
8.
When replacing either Q7 or Q8,
and before turning on the power, check
with an ohm-meter between transistor
case ani chassis to make certain that a
short circuit does not exist.
Note that
insulating washers aI'e placed under the
transistors to provide inSulation.
PRINTED CHASSIS COMPONENT REPLACEMENT
1.
CHECKING COMPONENTS
The components should be carefully check-
ed by measuring circuit voltages and res'-
istances bei'oI'e attempting to remove one
of the leads from the printed chassis.
Extreme care must be exercised in remov-
ing the lead to prevent damage to the
board or conductoI's.
This operation
-5-
should not be considered unless it is the
only way the component can be checked.
If one lead must be removed without dam-
abe to the component, apply a well clean-
ed and tin.Tled 25 to 60 watt iIon to the
fillet adjacent to the lead.
With small
long nose pliers
OT
thin screwdriver, pry
the folded portion of the
le~'~
in line
C~
.
,
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