Micro-Tech 600 Amplifier Service Manual
15
Electrical Checkout Procedures
TEST 12: OUTPUT POWER
Spec at 8 Ohm Stereo:
>= 235W at 0.1% THD.
Spec at 4 Ohm Stereo:
>= 340W at 0.1% THD.
Spec at 2 Ohm Stereo:
>= 410W at 0.1% THD.
International 8 Ohm Stereo:
>=220W at 0.1% THD.
International 4 Ohm Stereo:
>=275W at 0.1% THD.
International 2 Ohm Stereo:
>=300W at 0.1% THD.
Initial Conditions:
Controls per standard.
Procedure:
Load each channel to 8 ohms. Inject a 1 kHz
sine wave and measure at least 43.36 VAC at the
output of each channel. Load each channel to 4 ohms.
Inject a 1 kHz sine wave and measure at least 36.88
VAC. Load each channel to 2 ohms. Inject a 1 kHz sine
wave and measure at least 28.64 VAC. All power
measurements must be at less than 0.1% THD.
TEST 13: REACTIVE LOADS
Spec:
No oscillations. Safe with all types of loads.
Initial Conditions:
Controls per standard.
Procedure Capacitive:
Load each channel to 8 ohms in
parallel with 2 µF. Inject a 20 kHz sine wave with 33
VAC output for 10 seconds.
Procedure Inductive:
Load each channel to 8 ohms in
parallel with 159 µHenries. Inject a 1 kHz sine wave
with 15 VAC output for 10 seconds.
Procedure Torture:
Load each channel with the primary
(red and black leads) of a DC-300A transformer (D
5781-6). Inject a 15 Hz sine wave at sufficient output
level to cause 3 to 5 flyback pulses, for 10 seconds.
Procedure Short:
Inject a 60 Hz sine wave at 15 VAC
output. After establishing signal, short the output for
10 seconds.
TEST 14: ODEP LIMITING
Spec:
No oscillation on ODEP Limiting wave form;
either channel controls limiting in Parallel Mono Mode.
Initial Conditions:
Controls per standard; rag or other
obstruction blocking fan so that it does not turn.
Procedure:
Load the amplifier to 2 ohms on each
channel. Inject a 60 Hz sine wave and adjust for 15
Vrms at the output. After a few minutes observe a wave
form similar to Figure 5. Remove the input signal from
both channels and allow the amplifier to cool for a few
minutes. Switch the amplifier to Parallel Mono and
remove the load from Channel 1. Inject the signal into
Channel 1 and observe that ODEP limiting occurs at
the output of both channels. Remove the load from
Channel 2, and install the load on Channel 1. Again,
observe that both channels limit. Return all amplifier
controls to standard initial conditions. Remove the fan
obstruction.
TEST 15: LF PROTECTION
Spec:
Amplifier mutes for low frequency.
Initial Conditions:
Controls per standard.
Procedure:
No load. Inject a 0.5 Hz 6 volt peak-to-peak
square wave, or a 2 Hz 6VAC sine wave into each
channel and verify that each channel cycles into mute.
TEST 16: SIGNAL TO NOISE RATIO
Spec:
100 dB below rated 8 ohm power 20 Hz to 20
kHz. 105 dB A-Weighted.
Initial Conditions:
Controls per standard. Short inputs.
Procedure:
Load each channel to 8 ohms. Measure
less than 434 µV at the output of each channel (20 Hz-
20 kHz bandpass filter).
TEST 17: TURN ON TRANSIENTS
Spec:
No dangerous transients.
Initial Conditions:
Controls per standard.
Procedure:
From an off condition, turn on the amplifier
and monitor the output noise at the time of turn on.
Note: Turn on noise may increase significantly if the
amplifier is cycled off and on.
Figure 5. ODEP Limiting Wave Form
