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Old 25th October 2011, 09:44 PM   #1
Dr Zeus is offline Dr Zeus  United States
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Default Alpine MRV-F300

Got this small 4 channel amp in for repair. Channel 4 had a blown short B688 which I've replaced with some spares I took from another Alpine. The opposite D718 is measuring OK, as is the output driver, a C2682. All outputs and PS fets are measuring A-OK atm.

When power and REM is applied, the amp pulses a small ammount of rail voltage then imidiately turns right off. The cycle continues about every 3 seconds.

KIA494:
Pin 1: 0.040 pulses 0.400
Pin 2: 0.886 pulses 1.179
Pin 3: 0.080 pulses 0.310
Pin 4: 4.97 pusles 2.7
Pin 5: 1.480 pulses 1.600
Pin 6: 3.665 pulses 3.915
Pin 7: 0 pulses 0.2
Pin 8: 13.7 pulses 13.5
Pin 9: 0.020 pulses 0.725
Pin 10: 0 pulses 0.625
Pin 11: 13.7 pulses 13.5
Pin 12: 13.7 pulses 13.5
Pin 13: 4.97 pulses 5.03
Pin 14: 4.97 pulses 5.03
Pin 15: 4.97 pulses 5.03
Pin 16: 0 pulses 0.092
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Old 25th October 2011, 09:46 PM   #2
Dr Zeus is offline Dr Zeus  United States
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AAAAAAAAAAANND I just found a broken trace under the board!

Will report shortly
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Old 25th October 2011, 09:56 PM   #3
Dr Zeus is offline Dr Zeus  United States
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Fixing the trace seems to have fixed the issue. What should the rail voltage of this amplifier be? Someone (not me I swear) likely adjusted the rail-v pot.
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