Nakamichi PA-7EII Problems... - diyAudio
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Old 3rd March 2015, 10:38 PM   #1
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Default Nakamichi PA-7EII Problems...

Hey guys,

A friends got his hands on a hand-me-down Nak set, incl tuner, preamp and a PA-7EII. Problem is, when he got it, all it did was blow line fuses So anyway, he's asked me to try help him get it going.

First thing I noticed was that it appeared that the spark killer on the limiter board was bust, so replaced that with discrete resistor and cap. Still wouldn't budge, and I noticed that the primary wasn't being engaged at startup and continued to blow fuses.

Tried shorting across the soft-start relay terms and the lights came on for half a second and then the fuse blew again. Replaced the relay with a new solid-state dude, but the same thing happened, so I ruled out the relay and put the stock unit back as I figured it was ok.

Checked out the ballast resistor and that seemed blown. Replaced it and started it up again and the new alu-jacketed ballast resistor blew into a couple of pieces with a huge bang, but the lights came on just before.

So I'm kind of at a loose end from here on. It seems that something has made this amp intent on blowing the 2R2 ballast resistor for the soft-start.

Any help/ideas would be appreciated! And by the way, I've checked every answer to this on the net and haven;t yet found a probable solution.

Cheers!
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Old Yesterday, 01:11 AM   #2
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You need to hook it up to a dim bulb tester before you permanently damage something and turn it into a boat anchor. The DBT will at least keep the fuses from blowing and allow you to begin troubleshooting where the problem is at.

If it were me I'd disconnect the amplifier channels from the PS and then with it connected to the DBT power it on. The DBT should glow brightly for a second and then dim. You may have a dead rectifier or e-cap and this test will identify where the problem is at.
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Old Yesterday, 08:36 AM   #3
djk is offline djk
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You need to check the outputs for shorts, and the rectifiers and main filter caps as well.
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