Heathkit AA-1214 Assembly And Operation Manual page 49

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HEATHKIT
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49
AMPLIFIER SIGNAL INJECTION CHART
Refer to Figure 1-9 {fold-out from Page 44) for the following tests.
TEST IF YOU DO HEAR A MILD HUM
IF YOU DO NOT HEAR A MILD HUM
POINT OR CLICK FROM THE SPEAKER
OR CLICK FROM THE SPEAKER
TPl
Proceed to TP3 (left
l.
Check for poorly soldered or
(Left channel) channel) or TP4 unsoldered connections on
TP2
(right channel). the circuit board.
(Right channel)
2. Check transistors QlO5, QlO6
QlO7, QlO8, QlO9, QllO and
Qlll to make sure they are
not incorrectly installed or
interchanged.
3. Check diodes DlO2, DlO3, and
DlO4 to make sure they are
w
not installed backward or
interchanged.
4.
Check capacitors Cl31, Cl 32,
Cl37, Cl38, Cl41, and Cl42
to make sure they are not
incorrectly installed.
TP3
Proceed to TP5
l.
Check the shielded cables from
(Left channel) (left channel) or
the tone circuit board to the
TP6 (right channel)
amplifier circuit board to be
L..
sure the shield and inner
leads are not interchanged.
TP4 2. The inner lead and shield lead
(Right channel)
in the shielded cables from
the tone circuit board to the
amplifier circuit board may
be shorted together due to
melted insulation.
TP5 Proceed to TP7 (left
l.
Balance control or Volume
(Left channel)
channe 1) or TP8 control may be improperly
TP6
(right channel)
installed, poorly soldered,
(Right channel)
or faulty.
TP7
Proceed to TP9 (left
1.
Transistor Q2O1 may be
(Left channel) channel) or TPlO
incorrectly installed or
TP8
(right channel).
interchanged with another
(Right channel)
transistor .
2.
Poor connect i ons on the
Balance or Volume control .
l