Nakamichi PA-7II won't power on, limiter resistor blown - diyAudio
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Old 12th June 2015, 08:24 PM   #1
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Default Nakamichi PA-7II won't power on, limiter resistor blown

I've come across a non-functional Nakamichi PA-7II amp. It will not power on. I found that R504, the 20W resistor on the limiter PCB is blown. So I replaced it, and it immediately blew again. The thermal fuse in series with it is intact. Does anyone have any ideas as to what might be causing the resistor to blow?
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Old 12th June 2015, 09:50 PM   #2
gasgeek is offline gasgeek  United States
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Most likely the power transformer is shorted. R504 is acting as an inrush limiter until the relay kicks-in which is supplied by a secondary voltage from the transformer.
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Old 12th June 2015, 10:10 PM   #3
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Or a short circuit on a secondary winding.
Disconnect the secondaries and power it up with the 60W light bulb to replace the resistor.
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Old 13th June 2015, 01:07 AM   #4
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Wow, the power transformer would be difficult to replace I imagine. Can I just check for shorts on certain wires to/from the transformer?
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Old 13th June 2015, 06:56 PM   #5
wayne is offline wayne  United States
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Disconnect secondary from rectifiers as a test.
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