in the bridged mono mode. The increased current could
overheat the amplifier.
OPERATION
The
pilot lamp in the power switch will glow whenever
power is applied to the SEl20. If it does not light, check for
a blown AC line fuse.
The SE 120 is equipped with a unique protection system
that constantly monitors the temperature of the output
devices and takes corrective action to prevent damage to
the amplifier as a result of excessive overheating. Under
most conditions, the SE120 heatsinks will dissipate the
heat required to maintain safe operating temperatures, and
the unit will play continuously. If the amplifier is driven at
high volumes into speakers with an impedance of less than
8 ohms, and/or there is inadequate ventilation, the heatsinks
could heat to a level that would cause the protection
circuitry to shut off the amplifier for a short time (normally
less than 15 seconds) to prevent damage. The SE120 will
return to normal operation, and if the overheating condition
is still present, the cycle will repeat. In this case, check the
surroundings of the unit to insure sufficient air flow around
the heatsinks and through the vent holes. Otherwise, check
the load impedance connected to the outputs to see if it is
far below 8 Ohms.
FUSES:
The SE120 is supplied with a 5 Ampere Slo-Blo AC line
fuse and four power supply fuses. If one of these fails, it is
usually indicative of a fault which will require professional
service.
Bias current adjustment for the SE 120 needs to be
performed in the following manner:
1. No signal applied to the input, no load on the output of
the amplifier.
2. Line voltage to the amplifier should be set at the
nominal value for the area.
3. Adjust one channel at a time.
4. With the unit off, remove either the + or - rail fuse
5
in the right channel. Insert the ammeter across the
fuse holder. Make sure that the ammeter is set at
its highest current scale.
Turn the unit on and, after the unit has warmed up
for approximately one minute, adjust the ammeter
reading for lOOmA. Turn the unit off. AlIow the
unit to discharge before removing the ammeter and
replacing the fuse.
6. Repeat steps 4 and 5 for the left channel.
TRANSISTOR VOLTAGE VALUES-
DC
volts
with respect to circuit ground,
no signal applied.
NAME
Emitter
Base
co lle ctor
Ql
-.755
-.130
51.5
Q2
-.756
-.159
51.7
Q3
52.3
51.7
51.5
Q4
52.3
51.8
51.8
Q5
51.4
50.9
-12.90
Q6
52.1
51.5
50.5
Q7
51.0
50.4
1.294
Q8
-1.157
-.532
1.314
Q9
-51.4
-50.7
-1.151
QlO
-.578
-1.153
-53.5
Qll
.711
1.303
53.5
Q14
-.737
-.126
51.5
Ql5
-.755
-.130
51.5
Ql6
-.756
-.159
51-7
Q17
52.3
51.7
51.5
Ql8
52.3
51.8
51.5
Ql9
51.4
50.9
-12.90
Q20
52.1
51.5
50.5
Q21
51 .0
50.4
1.294
Q22
-1.157
-.532
1.314
Q23
-51.4
-50.7
-1.151
Q24
-.578
-1 .I53
-53.5
Q27
-.518
-.088
-53.8
Q28
-.737
-.126
51.5
Q12
Ql3
Q25
Q26
Source
Gate
Drain
.778
.087
53.8
-.518
-.088
-53.8
.778
.087
53.8
-.518
-.088
-53.8
IC VOLTAGE VALUES
IC
PIN #
1.
-48.9
2.
-52.2
3.
-49.7
4.
-53.9
6.
-52.1
7.
-48.7
8.
-38.5
-DCV -54.0
+DCV 54.0
4-
