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NAD 3130 left channel dropping.... dropped
NAD 3130 left channel dropping.... dropped
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Old 21st November 2018, 03:26 AM   #1
sdineen is offline sdineen  United States
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Join Date: Oct 2018
Default NAD 3130 left channel dropping.... dropped

Hi - I have a 3130 I picked up recently that was awesome for about 3 weeks, but then noticed the Left channel going. What seems to be typical, is you can put balance all the way to the left, raise the volume, and suddenly you break through some oxidation or whatever it is and are back in luck. However, it continued to drop. Now I am down to NO left channel. Here is what I did/know:

Sprayed all switches and pots, turning the hell out of them. CRC contact cleaner (DeOxit is on the way) on all and especially on the vol/bal pot but to no avail.

Soldered the few joints that looked like they may need it.

Checked all fuses. Swapped all fuses. Licked all fuses (kidding on that one... unless you tell me to try it.)

Checked speaker "breakers" as this apparently has no relay, and they seemed good for continuity across, then ALSO jumpered with no change.

Checked via headphones and confirmed one channel out, so doesnt appear to be power output stage? I then disconnected amp/preamp connectors (which I already cleaned) and ran to another amp from preamp plugs. Same deal, missing the channel.

YES, tried every source connection, and A/B speakers, etc, etc. Also looked for any swollen caps/fried resistors, etc. I see two resistors that seem a little toast (R447, R448 100 ohm) but still read 100 ohms pin to pin.

I also half assed tried to get ohm readings on the vol/balance pot, and from what I could tell, I was getting consistent readings or would replace pot outright and quick. :-/ Any help would be extremely appreciated.... even if a "well... these caps are known to go bad sometimes". I got nothing left in me right now after the deoxit delivery.
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Old 21st November 2018, 06:45 AM   #2
Ian Finch is offline Ian Finch  Australia
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Join Date: Apr 2010
Location: Coffs Harbour, NSW
Divide and conquer, right?
So you tried the output from the preamp and that was also dead in the left channel? Well, doesn't that say that the problem has been narrowed down to preamp's left channel? Just check that the left power amplifier is actually OK by swapping the R.pre-to-L.pwr leads anyway.

The possible problems in the preamp are the few electrolytic capacitors and switches , like tone bypass and input selector switch. Follow the schematic through, ignoring the phono amp. for the time being and focus on the other, unboosted inputs, to make life easier. You can attach a probe to an input signal and trace the signal backwards from the power amp. to the input, if you get lost. Don't expect clean signal at all points though, as you may be overloading the amp and getting gross distortion at some stages.
Here's a source of the road map, if you don't already have one: NAD 3130 - Manual - Stereo Integrated Amplifier - HiFi Engine
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If only I had listened....
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Old 21st November 2018, 01:36 PM   #3
sdineen is offline sdineen  United States
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Join Date: Oct 2018
Default THANKS!

I will do so today Ian, and appreciate the Link!
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Old 22nd November 2018, 02:45 AM   #4
sdineen is offline sdineen  United States
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Join Date: Oct 2018
Default One item confirmed....

Regarding " you tried the output from the preamp and that was also dead in the left channel? Well, doesn't that say that the problem has been narrowed down to preamp's left channel? Just check that the left power amplifier is actually OK by swapping the R.pre-to-L.pwr leads anyway." this is confirmed, the right channel preamp feeds through and plays/powers the left channel when swapped! Thanks! Oh..... is there an easy way to jumper around the pot to confirm it is NOT the problem? my Deoxit has been delayed till Friday..... :-/ On to testing anything else I can (connections/resistors) now.

Last edited by sdineen; 22nd November 2018 at 02:52 AM.
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Old 22nd November 2018, 03:16 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by sdineen View Post
is there an easy way to jumper around the pot to confirm it is NOT the problem?
Don't try to bypass the pot, the high gain could damage your speakers, or even the amp.
Just be patient and use the good preamp channel in the meantime.
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Old 22nd November 2018, 09:54 AM   #6
jaycee is offline jaycee  United Kingdom
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Location: Norwich, UK
If you've found the fault is in the preamp, it is likely the muting FET Q303. You can bridge over that to see if the fault goes away
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Old 23rd November 2018, 12:42 AM   #7
sdineen is offline sdineen  United States
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Join Date: Oct 2018
Quote:
Originally Posted by jaycee View Post
If you've found the fault is in the preamp, it is likely the muting FET Q303. You can bridge over that to see if the fault goes away
Yep, you are 100% correct, and confirmed working bridging (after comparing continuity to working FET to jumper). THANK YOU JAYCEE!!
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Old 23rd November 2018, 05:12 AM   #8
sdineen is offline sdineen  United States
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Join Date: Oct 2018
Is it safe to assume that a straight replacement is the route to take? Another E8452 - J111 and no swap out of both to something else/other (aka that may not be as likely to fail)? JFET N-Channel Switch: Amazon.com: Industrial & Scientific

Last edited by sdineen; 23rd November 2018 at 05:23 AM.
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