I did a stupid thing... (Nad C320 red light) - diyAudio
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Old 21st July 2011, 08:46 PM   #1
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Unhappy I did a stupid thing... (Nad C320 red light)

I was reading the Nad c320 service manual and decided to do the alighment procedure. Everything was going well until i shorted TP2 and R242 with the pin of my dmm....a spark came out the resistor, and now the led of the amp stays red instead going to green, plus the heatsinks of the drivers are getting really hot. I havent got any background in electronics, i m just doing really basic stuff: changing capacitors and resistors etc. I included a link to the service manual. If somebody has any insight on how to repair this little amp i would be grateful


nad_c-320_sm_[ET].pdf - 4.0 MB
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Old 21st July 2011, 09:53 PM   #2
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Take it to a repair place, as you likely caused most of the transistors on the board for that channel to blow.

Outputs are guranteed to be gone, same with the drivers.
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Old 21st July 2011, 10:21 PM   #3
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Replacing all semiconductor which you think it might have affected is a good start.
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Old 21st July 2011, 10:26 PM   #4
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Thanks for your input guys. For the past 6 months i was upgrading the parts of this amp and was very pleased so far...changed electrolytics to Black gate and Elna cerafine,ceramics to silver mica, carbon resistors to metal film, polyester caps to mkp1837. The amp was totally transformed. Anyway, next time i'll be more careful. Good thing i have spares of the output transistors, but i think it would be hard to find replacements for sd669/sb649. Are there any suitable replacements for these?

Last edited by skouliki; 21st July 2011 at 10:48 PM.
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Old 21st July 2011, 10:54 PM   #5
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BD139/140
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Old 21st July 2011, 11:16 PM   #6
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Confuscious he say if it its working leave well alone !

Done it myself, dropped my jewellers screwdriver while tweaking a pot.
Should have bought a plastic tweeker !
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Last edited by nigelwright7557; 21st July 2011 at 11:23 PM.
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Old 21st July 2011, 11:22 PM   #7
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Quote:
Originally Posted by nigelwright7557 View Post
Confuscious he say it its working leave well alone !

Done it myself, dropped my jewellers screwdriver while tweaking a pot.
Should have bought a plastic tweeker !
So true! And i have to add that only 3 hours of sleep after the night shift seriously impairs decision making and stability of hands.

Last edited by skouliki; 21st July 2011 at 11:42 PM.
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Old 22nd July 2011, 08:22 AM   #8
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Default Protection circuit was damaged....Q21 gone... and others may be dead too

You must send it to a skilled repairman if you do not feel yourself good to to that.

After night shift we are good for the bed only.

regards,

Carlos
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Old 22nd July 2011, 08:53 AM   #9
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Hi there,
Second source SB649/SD669, manufactured by Hi-Sincerity Microelectronics Corp of Taiwan, are available from eBay seller audiowind-2005.

They are marked as HSB649A and HSD669A, hFE grade C, and as far as I can tell from basic measuring apparatus meet the spec. The datasheet is available from the Hi-Sincerity website.

No connection, just a customer.

Hope this helps.

Regards

Angus
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Old 21st August 2011, 12:09 AM   #10
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Today i finally managed to replace the output transistors and the drivers but the amp still refuses to go out of protection mode.... any thoughts?
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