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Old 22nd September 2012, 12:27 PM   #1
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Default Nad 214 DC on output

Gooday,
I have Nad 214 power amp that developed scratching and hiss on one channel. I normally use 8 ohm speakers but I have hooked up 4 ohm speakers to test. The manual say's that the amp is 2 ohm stable , so there should not be a problem driving 4 ohm speakers. I haven't taken the cover off yet but I measured on the faulty channel between 25 - 202 mv DC. If I increase the volume then the music still plays fine, only when there is quiet passages you can hear the scratching. Does anybody have an idea what the problem could be ?

Regards
Jan
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Old 22nd September 2012, 12:47 PM   #2
pdul is offline pdul  Denmark
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It will be so much easier for someone here to give you a qualified answer, if you post a schematic of the mentioned amp
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Old 22nd September 2012, 02:00 PM   #3
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--- all Nad 214 will fail in the secondary power supply most electrolytics there are low quality and marginal when it comes to voltage and temperature
--- muting transistors in the input is something i disapprove and normally remove to all units
--- some other capacitors in various stages are also low quality probably worth looking at
---Given the chance you may upgrade the main power banks to something bigger since the pcb may accommodate more but only thin and tall as far as i remember
---Inspect IC 201 for soldering issues verify proper voltage there

---Input caps are also low quality .... some better and may be bigger cap there may be some improvement

---Tackle the protection relay to see for interrupt while in very low power mode if needed replace

---Inspect input plugs often there you have soldering issues especially if input plugs/cables are big or heavy

--Inspect the all unit for soldering issues

--last verify bias of the amplifier since the manufacturer of the amp ( depending on the serial number ) decided to decrease the bias on production to preserve some safety more while the designer on the service manual share some other opinion . Tune according to the schematic expect overall temperature to increase but just a bit .remember to warm up tune and verify more than once or twice if needed .


Offset may occurs if power supply of the first stages is not equal plus and minus .... there might be other reasons also

Kind regards
sakis
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Last edited by east electronics; 22nd September 2012 at 02:02 PM.
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Old 23rd September 2012, 08:46 AM   #4
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by pdul View Post
It will be so much easier for someone here to give you a qualified answer, if you post a schematic of the mentioned amp
NAD 214/216 service manual.

Wait until the text under the preview picture "This file is downloadable free of charge from the site... processing (please wait)" changes to "This file is downloadable free of charge from the site: Get Manual" and click on "Get Manual".

Last edited by jitter; 23rd September 2012 at 08:53 AM.
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Old 23rd September 2012, 10:49 AM   #5
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Thanks for the info you all and for the link to the manual ,
It seems this is only happening intermittently when the amp is getting hot. I'll be checking for dry joints and will check out Sakis suggestions during this week. I have downloaded the schematics but is having a story to attach it . On my way to game farm for the day, having a barbeque and some liquid refreshments, this is Africa after all !! Next week I'll jump into this problem Thank you all for helping and have a great day.
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Old 7th February 2013, 08:30 PM   #6
geolyd is offline geolyd  Denmark
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Quote:
Originally Posted by Vrystaat View Post
Thanks for the info you all and for the link to the manual ,
It seems this is only happening intermittently when the amp is getting hot. I'll be checking for dry joints and will check out Sakis suggestions during this week. I have downloaded the schematics but is having a story to attach it . On my way to game farm for the day, having a barbeque and some liquid refreshments, this is Africa after all !! Next week I'll jump into this problem Thank you all for helping and have a great day.
Hi Jan. any luck with your 214, mine has started having the same issues on the left channel, Thinking of ditching it or having it fixed and giving it to my sister next time I'm in Sefrica.
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Old 1st June 2013, 12:11 AM   #7
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Hallo to all,
And so it was, the terrible obnoxious DC offset was due to the caps. I have replaced all 40 off them. I have added two extra filter caps, I am a happy chappy. Had a looney bias pot but that was different story.
Thanks Sakis and the other wise people,the sound have improved a lot, What I can't understand is that this amp is not that old. 15 to 18 years maybe. It certainly depends on the quality of the original caps as well. Tomorrow I will have a few Ouzo's with the rugby. Thanks again Sakis ! I'm sure caps have to be reformed, it is the same as a battery, keep it charged, it has to go through it's cycles to keep it in form, but it takes a couple of day's. I do believe some electronic components needs time to settle.
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Jan
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Old 1st June 2013, 10:06 AM   #8
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you are welcome ... mind the ouzo and please verify bias after all changes
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SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
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