NC400 Problem

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zenpmd

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NC400 Problem
« on: 31 Jan 2015, 05:29 pm »
My amp has been working fine for months, but now its gone very weird. It just comes on for a 1 second, plays, then off for 2, on for 2 off for 2, on for 1 etc. Basically just cuts in and out. Sometimes stays on for 5 seconds. Any idea what the issue is? All connections seem fine

Julf

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Re: NC400 Problem
« Reply #1 on: 31 Jan 2015, 05:47 pm »
You say all connections are fine, but it does sound like either a short on the output, or possibly a DC offset on input.

jschwenker

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Re: NC400 Problem
« Reply #2 on: 31 Jan 2015, 06:05 pm »
As an nc400 owner-builder, I'm recalling that the manual has some detail in it about the internal on-off logic.  Seems like it spends a 2 second delay checking various lines for power, or "go" values from other areas and then it turns things on.  (when things are working right you hear that delay after flipping your power switch)  My guess is you might have one of those logic line connections that has gone unreliable.  If you're lucky it could be something as simple as getting in and de-mating/re-mating the connectors between power supply and amp units.  Good luck!

Cheers,  John

Julf

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Re: NC400 Problem
« Reply #3 on: 1 Feb 2015, 09:13 am »
As an nc400 owner-builder, I'm recalling that the manual has some detail in it about the internal on-off logic.  Seems like it spends a 2 second delay checking various lines for power, or "go" values from other areas and then it turns things on.  (when things are working right you hear that delay after flipping your power switch)  My guess is you might have one of those logic line connections that has gone unreliable.  If you're lucky it could be something as simple as getting in and de-mating/re-mating the connectors between power supply and amp units.  Good luck!

You are right about the delay. According to the flow chart there is a 0.5 second wait to sense DC offset, and a 2 second wait before checking the nAMPON signal, frequency and overcurrent. If nAMPON is floating, the amp never turns on.

If the amp turns on and off every 2 seconds, either the oscillating frequency is out of limits or there is an overcurrent condition (output shorted). Seems like a DC offset on the input would cause the amp to turn off (and stay off) after a 0.5 second delay.

zenpmd

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Re: NC400 Problem
« Reply #4 on: 1 Feb 2015, 09:29 am »
But what does all this mean to a stupid person like me :)

Julf

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Re: NC400 Problem
« Reply #5 on: 1 Feb 2015, 10:51 am »
But what does all this mean to a stupid person like me :)

That you most likely have a shorted output. Any chance of a stray strand of wire touching across the connectors or something?

zenpmd

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Re: NC400 Problem
« Reply #6 on: 1 Feb 2015, 11:45 am »
What is a shorted output?

Which wires in particular? Nothing has touched anything it shouldnt

zenpmd

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Re: NC400 Problem
« Reply #7 on: 1 Feb 2015, 11:48 am »
Very odd. Now I have gotten it playing for a couple of minutes and no problems....?

zenpmd

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Re: NC400 Problem
« Reply #8 on: 1 Feb 2015, 12:16 pm »
noq for like 30 mins....!

jtwrace

Re: NC400 Problem
« Reply #9 on: 1 Feb 2015, 01:02 pm »
First thing is to use a DMM and make sure the outputs are not shorting.  ALso, checking the dc offset wouldn't be a bad idea either.  Directions are here

Julf

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Re: NC400 Problem
« Reply #10 on: 1 Feb 2015, 01:12 pm »
What is a shorted output?

An unintentional direct connection between the output terminals.

Quote
Which wires in particular? Nothing has touched anything it shouldnt

Speaker output wires. Sometimes one single strand getting out of line and touching the other pole can be hard to spot.


Julf

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Re: NC400 Problem
« Reply #11 on: 1 Feb 2015, 01:14 pm »
First thing is to use a DMM and make sure the outputs are not shorting.  ALso, checking the dc offset wouldn't be a bad idea either.  Directions are here.

As long as you only *check* the dc offset. Do not touch the adjustments unless you really know what you are doing.


jtwrace

Re: NC400 Problem
« Reply #12 on: 1 Feb 2015, 01:18 pm »
As long as you only *check* the dc offset. Do not touch the adjustments unless you really know what you are doing.
It's not hard.  As I said, check it first and then adjust according to the directions I posted. 

zenpmd

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Re: NC400 Problem
« Reply #13 on: 2 Feb 2015, 07:24 am »
More symptoms today. After writing yesterday I had literally 8 hours of constant performance out of it. Perfect, no issues, no when turning on this morning its off and on... surely that means something? In addition, when playing but volume set down inaudible, the speaker omits a very very light periodic pop, one of a slightly higher pitch, the other of a slightly lower pitch..

Julf

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Re: NC400 Problem
« Reply #14 on: 2 Feb 2015, 07:52 am »
It's not hard.  As I said, check it first and then adjust according to the directions I posted.

I would still recommend only adjusting it if it really is outside of the specifications.

Julf

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Re: NC400 Problem
« Reply #15 on: 2 Feb 2015, 07:54 am »
More symptoms today. After writing yesterday I had literally 8 hours of constant performance out of it. Perfect, no issues, no when turning on this morning its off and on... surely that means something? In addition, when playing but volume set down inaudible, the speaker omits a very very light periodic pop, one of a slightly higher pitch, the other of a slightly lower pitch..

Can you borrow an oscilloscope and check the switching frequency? And definitely measure the DC offset.

zenpmd

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Re: NC400 Problem
« Reply #16 on: 2 Feb 2015, 12:02 pm »
I thought I should buy a fluke multimeter as they are supposed to be good - but they are expensive! Will a basic one like this be ok for my uses?

http://www.ebay.co.uk/itm/Fluke-101-Handheld-Digital-Multimeter-/331435959455

jtwrace

Re: NC400 Problem
« Reply #17 on: 2 Feb 2015, 12:53 pm »
I would still recommend only adjusting it if it really is outside of the specifications.
Once again, check first and adjust if needed. 

Julf

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Re: NC400 Problem
« Reply #18 on: 2 Feb 2015, 01:29 pm »
I thought I should buy a fluke multimeter as they are supposed to be good - but they are expensive! Will a basic one like this be ok for my uses?

http://www.ebay.co.uk/itm/Fluke-101-Handheld-Digital-Multimeter-/331435959455

Any $5 one is enough for basic stuff.

Julf

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Re: NC400 Problem
« Reply #19 on: 2 Feb 2015, 01:31 pm »
Once again, check first and adjust if needed.

And the "if needed" means "is out of spec". What I worry about is the usual OCD audiophile finding a 10 mV DC offset (well within specs) and trying to "optimize" it to 0, only to find that it is -15 mV the next day...