The Mighty NEC A-10II Integrated

[pashka]

That seemed excessive, but mine does run VERY hot, so I run two cooling fans over the vents above the heatsink.

Wow , mine runs all time little warm . sometimes i keep amp on 24/7 better sound .
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Other vintage unomaly :
"Phono Selector" MM & MC .
I can play records only on MM Selector , its fine on MM , but on MC no high range , its playing like without tweeters , signal cuted somewhere around 6Khz .


And other interesting things , I check a lot of websites must Japan about recap , restore NEC A-10II and funded nobody touch, replays large capacitors (x8 ).

 

[pashka]

Thanks for those links. I've stumbled upon them before, and read about the relays and the power switch light. Mine is out also, and when I measured the 46 volts, I scratched my head and said, "that's strange, but whatever - I can live with it being out." LOL It would be nice to get it working again, though.

I wanted to replace the thermal grease on all the outputs just for routine maintenance, but to get to them, you have to remove about three dozen screws - including the transformers. That seemed excessive, but mine does run VERY hot, so I run two cooling fans over the vents above the heatsink.

Try to adjust the voltage as stated in service manual Maybe this will help.
Next grab info from japan website translate by google.

 

[Hifirob2]

Interesting information - thanks. My DC offset is so low as to not worry me. I doubt mine needs any alignment adjustment - that would affect sound quality, and mine sounds great. The heat I get is due to the design of the heatsink. NEC specifically designed the heatsink with closed cells on the bottom and all four sides (only the top is open) - so as to eliminate any possible vibration. This was in accordance with everything else on the A-10II that was designed to reduce any possible vibrations (the extra bracing, thick bottom plate, and even the special alloy feet) to achieve the best sound quality. NEC also did this with a few of it's CD players in the mid 80s. Whether all this design slant resulted in better sound is up for debate, but take a look at the heatsink design. It's completely closed - there is no way for normal air convection to help keep it cool. The inside chambers of the heatink become an oven. If it was a normal "finned" design, it would probably do it's job just fine. But I need the help of a fan to draw more air up through the bottom to help dissipate all that heat. Otherwise, the outputs would slowly cook themselves to death - which is (from what I've read online) what happens on these amps from time to time. People blame the transistors themselves - saying they weren't designed for such high voltages. That just isn't true. These same outputs are used in the MCS 3872 integrated amp (also made by NEC - in 1985). In that amp, the voltages are much higher - as the amp is rated at 110 watts per channel. That amp has a normal heatsink, and is very stable - no overheating issues at all. The data sheet for these outputs states says they can be safely used in amps up to 120 watts per channel, so when used in a 60 wpc amp, they perform just fine - as long as they stay cool. Cooling fans are a very inexpensive insurance policy to keep this amp running for many years.

 

[pashka]

I have ID , just get quiet fans for laptop , and plays under NEC .
I have one for my mac mini , too noise .
Need check market for quiet one .

 

[pashka]

Hifirob2, do you recap yours NEC ?

 

[Hifirob2]

No, I haven't replaced any caps - everything is original. Most of the caps (including the 8 big ones) are audio grade, and replacing those will get VERY expensive.

I wouldn't place a fan under the amp - there may not be room for proper circulation - unless you raise the amp up a few inches maybe. It may also deposit a lot of lint and dust directly onto the transistors (since they face the bottom) - making them run even hotter. I use this fan:

http://www.ebay.com/itm/Microsoft-X...050613?hash=item4b0138db75:g:dJ0AAOSwJcZWgZAy

It's from an old Microsoft Xbox 360. It 'hovers' above the vents over the heatsink so any vibrations from the fan don't enter the amp. It's designed to run on 12 volts DC, but I run it at around 4-6 volts, so that it is very quiet. Works perfectly.

 

[pashka]

I know how to solder, but do not understand wiring diagrams what can be problem if somebody цан ме help .

With a high voltage on the light bulb I have not yet figured out, and I do not have enough knowledge. As far as I understand from the Japanese site must be replaced two transistors TR161 TR162 FET(2SK105)



I enclose a scheme of what they want in the settings I did not understand.



Is voltage on bulb can be normal , if Im replays 2 transistors TR161 TR162 ???




If need more info , i have it .



Listening at low volume.

 

[Hifirob2]

From what I can tell, TR161 & TR162 are located on the phono EQ board, and should have nothing to do with the power light voltage. The transistors in the lamp circuit are TR301 & TR302, along with several resistors. The high voltage on the lamp is normal as far as I can tell. My A-7 lamp also uses full rail voltage. I'm sure there is some LED conversion that could fix it, but I haven't looked into it.

Why are you listening at low volume?

 

[pashka]

Why are you listening at low volume?

I like it when the volume does not exceed the volume of the human voice, sometimes I power up and listening a large volume but usually listen moderately.

Regarding the voltage on the bulb. I do not think that 46 volts is normal voltage for 9 Volt bulb. LEDs burn out very quickly and to the same resistance heated onboard switching speakers.

On a photo of a Japanese web site with a clumsy translation of Google I never could understand that he replays that he restore the voltage at 9 volt.
My english is also bad


This is diagram speakers switch board and "Protector Circuit " Two board connecting P303 --> P609

 

[Hifirob2]

I don't think it's an LED, as green LEDs use a voltage somewhere around 2.0 - 3.8 volts. It's a filament type bulb (similar to the ones used in the previous generation of NEC gear (including the A820, T-6, T-651, and K525) that runs at a higher voltage. These small, filament type lights burn out quick - LEDs last for many years.

Did you measure the voltage after the resistor (R324)? It is a 47 ohm 1/2 watt resistor that comes between the B+ voltage and the light bulb. Is that where you are getting 9 volts?

 

[pashka]

I

Did you measure the voltage after the resistor (R324)? It is a 47 ohm 1/2 watt resistor that comes between the B+ voltage and the light bulb. Is that where you are getting 9 volts?

Thanks Hifirob2 ,
While I do not have time to measure the resistance . I measured the voltage at the contacts of the bulb without the schematic information. As soon as the time to disassemble and measure, I will answer here.

 

[Hifirob2]

No need to do it quickly - unless you are going to be in there fixing something else. It's just curious that there may be so much voltage going to a light - and I'm in no hurry to replace mine, because it takes so long to disassemble. So many screws....

 

[SoundsAlike]

No, I haven't replaced any caps - everything is original. Most of the caps (including the 8 big ones) are audio grade, and replacing those will get VERY expensive.

I wouldn't place a fan under the amp - there may not be room for proper circulation - unless you raise the amp up a few inches maybe. It may also deposit a lot of lint and dust directly onto the transistors (since they face the bottom) - making them run even hotter. I use this fan:

http://www.ebay.com/itm/Microsoft-X...050613?hash=item4b0138db75:g:dJ0AAOSwJcZWgZAy

It's from an old Microsoft Xbox 360. It 'hovers' above the vents over the heatsink so any vibrations from the fan don't enter the amp. It's designed to run on 12 volts DC, but I run it at around 4-6 volts, so that it is very quiet. Works perfectly.

Have you ever measured the temperature? MY A-7II gets up to 140F degrees. My Apple iMac gets up to 150F degrees under high processor loads. My tech friend and some informed posts on audiokarma, indicate that 140-150 is well within an acceptable or expected temperature range for circuits.

 

[Hifirob2]

Have you ever measured the temperature? MY A-7II gets up to 140F degrees. My Apple iMac gets up to 150F degrees under high processor loads. My tech friend and some informed posts on audiokarma, indicate that 140-150 is well within an acceptable or expected temperature range for circuits.

I haven't measured the real temp., I just know it puts out more heat than I'm comfortable with. This amp is known for running very hot, so a cooling fan makes me feel like I'm not risking any damage to it. That, along with the poor heatsink design, and this amp is begging for a cooling fan. Better safe than sorry.

 

[pashka]

Hm. My NEC is warm , not hot . On the top of amp when I touch feel warm much less then my mac . My Mac Mini is really hot , I can keep hand on mac , but I feel is look like hot coffee cup then you can keep it and drinks .
Then I got this Nec fitrst one clean all inside and check all contacts everywhere , it was looking good, no burning places .


I have question !


My NEC sounding unbelievable sweet and massive and so on , but after 2-3 hours , maybe 4hrs
Is it normal for this class AMP ? OR I NEED TO DO SOMETHING LIKE RESTORE , RECAP ... ?????????


Thanks . Paul

 

[Hifirob2]

If you are saying that the amp sounds better after a few hours of play, then that's pretty normal. I leave mine on for hours at a time just for that reason. I have other NEC amps that behave similarly, and have read where other owners think it sounds better after some "warm up" time. Maybe it's the caps sounding better after time, or maybe it's our ears "adjusting" to the sound quality.

If the sound deteriorates after a couple of hours or so, with distorted bass or loss of bass, then caps in the power supply are probably dried up, and need to be replaced. That's a common issue with this amp's matching tuner, the T-6.

 

[pashka]

Thanks Hifirob2 .
So mine is OK.

 

[pashka]

Is some body need wiring diagram, service manual for NEC A-10II , I have it .

 

[Bostown]

Is some body need wiring diagram, service manual for NEC A-10II , I have it .

Ive got an A-10 II that works but definitely needs TLC. , great unit, and clearly not something you see everyday. Ill eventually get around to servicing it and the NEC M-50 monos ive been hoarding.

 

[arnold_a1968]

Hello, just got my A-10ii and power lamp is busted, any idea where to get lamp replacement?