A and T Labs
K6 Audio Power Amplifier Assembly Manual
2001 A and T Labs Inc.
AMK6a
14
Temporarily connect the shutdown input pin to +12 volts and verify that the output
voltages are turned off.
4.2 ALTERNATIVE INVERTER TESTING CHECKLIST (If an oscilloscope is
available)
After installing all components, except fuses, check component values and
orientations again carefully
Install fuse F2 only and check for the presence of +/- 12 (+/- .5) volts at the output of
regulator IC3 (Reg1) and D13 respectively
If an oscilloscope is available, a very useful test that is highly predictive of
operational success of the power supply is possible:
(Very Important !!: Be sure
your scope is operating ungrounded with respect to the AC power line for
these tests!)
Check the gate drive waveforms at the power transistors (from gate to source) with
fuse F2 installed and fuses F1 and F3 left out. This a/- 12 volt control voltage
without applying rectified line voltage to the power transistors. What you should see
is approximately 75Khz, somewhat rounded square waves, with the signals at Q1
and Q2 in phase, and those at Q3 and Q4 in phase, and both pairs 180 degrees out
of phase with each other.
If the appropriate signals are not found, backtrack to IC1, verifying the square wave
output and proper installation of T2.
Next, install F1 and verify the presence of 320 (+/- 5%) volts at the input to fuse F3.
Install fuse F3 and check for proper output voltage (as set by the S2 switch setting)
at the output terminals. This may be a little bit high if no load is applied.
Apply a resistive load to the output, (for example 5K, 5 Watt) and check that the
voltage stays at the value expected for the particular S2 switch setting. Calculate the
load according to V=IR or P=(V*V)/R, and choose loads that are within the power
range of the supply, and that can dissipate the power without burning up!
That should do it! If you get to this point successfully, then your power supply
should have no trouble running the amplifiers!
If you have trouble with these last tests, for example if the shutdown LED operates
(which will typically be in the form of a pulsating cycle with the LED operating, and
