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Old 10th January 2015, 09:27 AM   #1
ftpols is offline ftpols  Japan
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Default NAKAMICHI IA-2 AMP HELP

Hi,

I just purchased a used Nakamichi IA-2 amp. Nice piece of gear but there is a very loud hum from LH channel when switched to Phono and there is no signal source. (All other selection are silent.)

Also, the trouble and strife says the reproduction is metallic...

Could somebody kindly advise about troubleshooting?

Many thanks!

Ftpols
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Old 10th January 2015, 09:33 AM   #2
Mooly is online now Mooly  United Kingdom
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To evaluate the phono input you must apply shorting plugs. If the input is floating then hum/noise pickup is normal although both channels would usually be similar. Short the inputs and see if the hum remains. If it is faulty then you will need a circuit diagram to see what is going on. It sounds an odd fault (if it is faulty) and could even be something like broken or cracked print somewhere (transit damage).
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Old 11th January 2015, 04:51 AM   #3
ftpols is offline ftpols  Japan
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Default NAKAMICHI IA-2 AMP HELP + SERVICE MANUAL

Quote:
Originally Posted by Mooly View Post
To evaluate the phono input you must apply shorting plugs. If the input is floating then hum/noise pickup is normal although both channels would usually be similar. Short the inputs and see if the hum remains. If it is faulty then you will need a circuit diagram to see what is going on. It sounds an odd fault (if it is faulty) and could even be something like broken or cracked print somewhere (transit damage).
Many thanks for your kind advice, Mooly.

I connected the shorting plugs and a cable from the GND terminal to grounded mains socket. I also sprayed Electrolube in the MM/MC phono selector switch and operated it 20 times.

With the phono MM/MC selector switched to MM, there is a whisper of white noise/pink noise from the left channel at full volume. When the phono selector is switched to MC, however, white noise/pink noise is very prominent on left channel at low volume.
Otherwise the amp is fine. It's years since I used an MC tone arm and turntable, so I guess it's no big deal.

Unfortunately, I can't upload the service manual because the file size is excessive.

TX.
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Old 11th January 2015, 08:06 AM   #4
Mooly is online now Mooly  United Kingdom
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So the hum has gone under these conditions. It should be silent (for hum) with just the shorting plugs and no separate wire.

White/pink noise will be "electronic" in nature with differences between channels caused primarily by differing semiconductors L vs R. There should not be any great difference though... first thought is to check whether the MM/MC switch really is functional and changing the gain on the channel that stays quietest. A large increase in noise is normal in the MC position.
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Old 13th January 2015, 01:25 PM   #5
ftpols is offline ftpols  Japan
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Default NAKAMICHI IA-2 AMP HELP + SERVICE MANUAL

Quote:
Originally Posted by Mooly View Post
So the hum has gone under these conditions. It should be silent (for hum) with just the shorting plugs and no separate wire.

White/pink noise will be "electronic" in nature with differences between channels caused primarily by differing semiconductors L vs R. There should not be any great difference though... first thought is to check whether the MM/MC switch really is functional and changing the gain on the channel that stays quietest. A large increase in noise is normal in the MC position.
Many thanks again, Mooly.

I will check the MM/MC switch next weekend.

Best regards,
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Old 13th January 2015, 01:32 PM   #6
Mooly is online now Mooly  United Kingdom
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OK, good luck
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