I am seeing an odd problem on one channel of a Mark Levinson 331 amplifier I am hoping someone can help me with. With no power cord connected but the large power supply capacitors charged from previous power applied to the amp, the output on one channel has 5.3 mV DC. With the power cord plugged in, but the unit completely off, there is 328 mV DC. Pressing the power button once, which puts the unit in standby, there is 1.7V DC. Pressing the power button again to place the amp in operate mode the unit shuts off. I presume this is due to the protection circuit sensing the high DC voltage on the output.
After removing all the power transistors, I performed a diode test on them and they all pass. Any ideas where I should look?
After removing all the power transistors, I performed a diode test on them and they all pass. Any ideas where I should look?
You've been left alone for 12 hours.
Downloading or purchasing a schematic diagram will be key. I typed levinson 331 in bing and got no obvious free responses, although this thread looks possible: PlayAgainAudio: Restoring Mark Levinson No. 331 Power Amp from Water Damage
Amps have circuits that turn output transistors on slightly, both the NPN and PNP, to limit crossover distortion. When these circuits get out of balance, DC on output can occur. Pot wipers can be bad, zener diodes/references in power supply voltages can be bad, electrolytic capacitors can be leakiing, tin or brass connectors can be oxidized and blocking low level signals.
Which of the above is the culprit will require some tests to find. Which will require a schematic diagram and parts layout on an amp this late in design.
Best of luck.
Downloading or purchasing a schematic diagram will be key. I typed levinson 331 in bing and got no obvious free responses, although this thread looks possible: PlayAgainAudio: Restoring Mark Levinson No. 331 Power Amp from Water Damage
Amps have circuits that turn output transistors on slightly, both the NPN and PNP, to limit crossover distortion. When these circuits get out of balance, DC on output can occur. Pot wipers can be bad, zener diodes/references in power supply voltages can be bad, electrolytic capacitors can be leakiing, tin or brass connectors can be oxidized and blocking low level signals.
Which of the above is the culprit will require some tests to find. Which will require a schematic diagram and parts layout on an amp this late in design.
Best of luck.
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