AP2020 \ VX1200 Power Amplifier
AP2020 \ VX1200 Power Amplifier
( Dec 6 2001 )
Visual Inspection and Test Setup
(See Appendix A)
Line Current
The amp draws less than 1.0 ampere while idling.
Bias
Measure 3 mVdc between testpoints TP9 and TP10 (R83 and R85).
The acceptable range for bias is 1 to 5 mVdc. Repeat for Channel B.
Power LED
:The Power LED should be ON , PROTECT LED OFF.
DC Supply Voltage Levels (No Load)
4 Ohm
2 Ohm
VM+
+ 54.6 +
47.8
+/- 1.0 Vdc
V(LN) = 120 Vrms
.
VH+
- 96.6 -
84.9
+/- 1.0 Vdc
Regulated DC:
16.8 +/- 0.5 Vdc
DC Offset Voltage
: < 25 mVdc
RMS Noise Voltage
: < 1 mVrms
GND LIFT
: Switch in to lift ground. Oscilloscope waveform has 60 Hz HUM component.
POWER AMPLIFIER (Amplitude Response):
Vin = -10 dBV
20 Hz
- 0.9 dB
200 Hz
0.0 dB
2000 Hz 0.0 dB
20000 Hz
- 1.1 dB
BASS CUT
:
Output drops 7 dB at 20 Hz
Turn On Delay
:
The output is delayed for 4 seconds after the power switch is turned On.
Cooling System
(i) Measure DC Voltage at TP1 on the Power Supply board while driving ChA into 4 ohms.
Keep ChB Volume control to minimum. This will result in heating only Ch A.
Observe TP1 rising from 3.0 to 3.5 Vdc due to ChA Temperature Sensing.
The cooling fan starts running at low speed.
(ii) Turn ChA Level control to minimum and ChB to maximum to start heating ChB and cool ChA. Soon the voltage at
TP1 will start to rise at 100 mVdc every 10 seconds due to ChB heating up.
(iii) Apply a small burst of Freeze Mist to the temperature sensor in the ChB heatsink. This should cause the fan to
slow down and the voltage at TP1 to drop. We now know that both temperature sensors are functioning
independently.
(iv) Allow ChB to heat up until the amplifier goes into Thermal Protect ( ShutDown ). This should happen when TP1
reaches 5.6 Vdc . At this point the fan should be running at fill speed.
(v) Put a lid on the unit. Make sure it cools down and comes out of PROTECT.
Fan Noise
Make sure the fan is running quietly at all speeds of operation.
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