Micro-Tech 600 Amplifier Service Manual
14
TEST 4: AC POWER DRAW
Spec:
100 Watts maximum quiescent.
Initial Conditions:
Controls per standard.
Procedure:
With no input signal and no load, measure
AC line wattage draw. If current draw is excessive,
check for high AC line voltage or high bias voltage.
TEST 5: COMMON MODE REJECTION
Spec at 100 Hz:
–70 dB.
Spec at 20 kHz:
–50 dB.
Initial Conditions:
Controls per standard.
Procedure:
No load. Inject a 0 dBu (.775VRMS) 100 Hz
sine wave into each channel, one channel at a time,
with inverting and non-inverting inputs shorted to-
gether. At the output measure less than –44 dBu
(4.9mVRMS). Inject a 0 dBu 20 kHz sine wave into
each channel, one channel at a time, with inverting and
non-inverting inputs shorted together. At the output
measure less than –24 dBu (49mVRMS). For Main
Modules with board numbers lower than D 7993-5
adjust N100 and N200 to calibrate CMR. For Main
Modules with board number D 7993-5 or greater
adjust R921 and R1021.
TEST 6: VOLTAGE GAIN
Spec 26dB Gain:
Gain of 20.0 ±3%.
Spec 0.775V Sensitivity:
±6%.
Spec 1.4V Sensitivity:
+12%/–6%.
Initial Conditions:
Controls per standard.
Procedure:
No load connected. Inject a 0.775 VAC 1
kHz sine wave with the Sensitivity Switch in the 26 dB
position. Measure 15.5 VAC ±0.5 VAC at the amplifier
output. Inject a 0.775 VAC 1 kHz sine wave with the
Sensitivity Switch in the 0.775V position. Measure 43.4
VAC ±2.6 VAC at the amplifier output. Inject a 1.4 VAC
1 kHz sine wave with the Sensitivity Switch in the 1.4V
position. Measure 43.4 VAC +5.2/–5.6 VAC at the
amplifier output. Return the Sensitivity Switch to the 26
dB position.
TEST 7: PHASE RESPONSE
Spec:
±10° from 10 Hz to 20 kHz at 1 Watt.
Initial Conditions:
Controls per standard, 8 ohm load on
each channel.
Procedure:
Inject a 1 kHz sine wave and adjust for 1
Watt output (2.8 VAC). Check input and output signals
against each other, input and output signals must be
within 10° of each other.
Electrical Checkout Procedures
TEST 8: LEVEL CONTROLS
Spec:
Level controlled by level controls.
Initial Conditions:
Controls per standard.
Procedure:
No Load. Inject a 1 kHz sine wave. With
level controls fully clockwise you should see full gain.
As controls are rotated counterclockwise, observe
similar gain reduction in each channel. When com-
plete, return level controls to fully clockwise position.
TEST 9: CURRENT LIMIT
Spec:
Current Limit at 20 Amps, ±2 Amps
Initial Conditions:
Controls per standard.
Procedure:
Load each channel to 1 Ohm. Inject a 1 kHz
differentiated (or 10% duty cycle) square wave. See
figure 4. Increase output level until current limit oc-
curs. Current limit should occur at 20 ±2 Amps (20
Vpk). Observe clean (no oscillations) current clipping.
In
Out
.047 uF
1K Ohm
Figure 4. Differentiator Circuit
TEST 10: SLEW RATE & 10 KHZ SQUARE WAVE
Spec:
13 - 15 V/µS.
Initial Conditions:
Controls per standard.
Procedure:
Load each channel to 8 ohms. Inject a 10
kHz square wave to obtain 52 volts peak-to-peak at
each output. Observe the slope of the square wave. It
should typically measure 13 to 15 V/µS. Also, the
square wave must not include overshoot, ringing, or
any type of oscillation.
TEST 11: CROSSTALK
Spec:
-60dB at 20 kHz.
Initial Conditions:
Controls per standard. Terminate
input of channel not driven with 600 ohms.
Procedure:
8 ohm load on each channel. Inject a 20 kHz
sine wave into the Channel 1 input and increase output
level to 33 VAC. Measure less than 33 mVAC at the
output of Channel 2. Inject a 20 kHz sine wave into the
Channel 2 input and increase output level to 33 VAC.
Measure less than 33 mVAC at the output of Channel
1.
