Repairing a 35-yo #Marantz PM-55 amplifier. I wish all electronic devices were as easy to service. There is a removable plate on the bottom of the enclosure for direct access to the track side of the main PCB. This is a nice addition, probably increasing manufacturing costs but making my life much easier.
The service manual is detailed with expected idle voltages at almost any point of the circuit. There was a numbering error on the schematics on the automute IC pins but this is a minor detail.
[#]electronics #fix #audio #repair
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It looks like the problem was just some dried solder joints around the voltage amplifier IC, as poking the pins with the meter probe suddenly disengaged the speaker proctection. The STK3062 is known to run very hot despite the heatsink, so maybe it accelerated the joint aging. I reworked the joints but I need more tests to confirm everything is O.K. now.
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