NKI1480B DAX60 and DAX120 Amplifiers—Installation
Page 12 of 18 (Jul-98)
On the DAX12O: Connect the meter's negative lead to the amplifier common at
Connector "J1-13." As you locate each DC voltage on the schematic, note the
number of the nearest "J" terminal in that leg of the circuit and, if possible, take the
readings between such a “J” terminal and "J1-13."
Measuring AC Voltages
AC voltages are printed without boxes at various points on the schematic. When
measuring these voltages on the amplifier, use an AC meter with a one-megohm
impedance and proceed as follows:
Step 1. Place the amplifier on a suitable work surface. Disconnect the speakers 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).
DAX12O: 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 approximately 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 increase
the output from the 1-KHz signal source until you obtain the rated output voltage
from the DAX. 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 DAX12O: 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 possible, 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 DAX6O, Q501-Q504 on the DAX12O) 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.
