Step 1.
Place the amplifier on a suitable work surface. Disconnect the speak-
ers and replace them with a suitable resistive load:
DAX6O: The load should have at least a 60-watt power rating and a value of
10.4 ohms across the 25-volt output (or 83.3 ohms across the 70.7-volt
output).
DAX120: The load should have at least a 120-watt power rating and a value of
5.2 ohms across the 25-volt output or (41.6 ohms across the 70.7-volt
output).
Step 2. Disconnect any input device and connect a one-kilohertz signal source
in its place. The source should be able to provide an amplitude of approxi-
mately 300 millivolts. Leave its output level turned down.
Step 3. Plug the amplifier into a 120-VAC, 60-HZ source. Turn the input-level
control fully clockwise, for maximum gain.
Step 4. Connect the test leads across the 25-V or 70.7-V outputs. Slowly in-
crease the output from the l-KHz signal source until you obtain the rated
output voltage from the DAK. Check the input level required to obtain the
rated output: a reading of 300 millivolts or less is an indication that the
amplifier gain is functioning properly.
Step 5. On the DAX6O: Connect the meter's negative lead to the amplifier common
at Connector "T-14." As you locate each AC voltage on the schematic, note
the number of the nearest "T" terminal in that leg of the circuit and, if
possible,
take the readings between such a "T" terminal and "T-14."
On the DAX120: Connect the meter's negative lead to the amplifier common at
Connector "J1-13."
As you locate each AC voltage on the schematic, note the
number of the nearest "J" terminal in that leg of the circuit and, if possi-
ble, take the readings between such a "J" terminal and "J1-13."
Locating the Driver and Power Transistors
On both amplifiers, driver transistors Q505 and Q506 are screwed to the
"L" bracket that is fastened to the large heat sink from inside the chassis.
The power transistors (Q507-Q508 on the DAX60, Q5Ol-Q504 on the DAX120) are
fastened directly to the large heat sink from the outside (to access them,
remove the protective cover). The transistors are numbered in ascending order,
with the lowest number at the bottom.
Removing and Replacing Transistors
Transistors are inherently long-lived devices that normally should not
need replacement. If, however,
systematic troubleshooting indicates a problem,
observe these precautions when removing and replacing transistors:
(1) Transistors can be damaged by excessive heat,
so use a small soldering
iron when removing or replacing a transistor with solder connections.
(2) Transistors come with a wide variety of cases and leads. To avoid a cost-
ly mistake, make a careful sketch of the lead connections before removing
a transistor from a printed circuit board or tie points.
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