Recommendations re Nakamichi IA-2 maintenance - diyAudio
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Old 10th January 2015, 08:27 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, 08:33 AM   #2
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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, 03:51 AM   #3
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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, 07:06 AM   #4
Mooly is offline 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, 12:25 PM   #5
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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, 12:32 PM   #6
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OK, good luck
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Old 4th April 2016, 07:57 AM   #7
ftpols is offline ftpols  Japan
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Smile Recommendations re Nakamichi IA-2 maintenance

The passives in my amp are 25 years old. But none of the caps (mostly Nichicon) are bulging or leaking - photos attached. The amp sounds fine.

I was thinking about preventative maintenance but don't have the time to replace the scores of transistors. And I excluded the phono PCB because I don't use it. Apart from replacing the other electrolytic caps are there any other parts that I should be focusing on, for example, the MOSFETS?

Also, I noticed that the heat sink never gets warm and wondered how effective are the TIM sheets between the MOSFETS and heat sink. I wonder if 3M 8810-2X36 Thermal Interface Material I have would be better.
Amazon.com: 3M 8810 Thermally Conductive Double-Sided Bonding Tape, 0.010" Thick, 2" Wide x 36 yards, 1 Roll: Industrial & Scientific

Many thanks for your recommendations, especially regarding manufacturers and part #s.
Attached Images
File Type: jpg Power Amp PCB.JPG (138.3 KB, 158 views)
File Type: jpg Phono PCB.JPG (133.4 KB, 152 views)
File Type: jpg Power Supply PCB(1).JPG (134.0 KB, 87 views)
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Old 4th April 2016, 08:20 AM   #8
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The only components that will need replacing are those that deteriorate. The only components that will consistently deteriorate (whether you hear or see it or not) are electrolytic capacitors. After 25 years, replace them - replace them all methodically, one channel at a time so you always have a working reference amplifier in case of problems.

Replacing other components without good reason, such as you may find in other brand amplifiers that have a reputation for early failure, would just be window-dressing.
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Old 4th April 2016, 08:58 AM   #9
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Is it faulty? If not leave it alone. Components chosen by the manufacturer are of excellent quality and last year after year after year. Semiconductors fail from time to time and until then, leave as it is. The conductive insulator pads used exceed the 3m stuff that you have your eye on.
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Old 4th April 2016, 09:44 AM   #10
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Hi, Ian.

Many thanks for your kind support. Further questions if you don't mind.
1. Would I need to change those two big beasts in the fuzzy photo of the Power Supply PCB?
2. Any recommendations re swapping the Power Supply and Power Amp electrolytics from Nichicon->Panasonic?
3. Re my comments about the heat sink not getting warm, the interfacing MOSFETS should be OK?

Have a nice day in Coffs Harbour.
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