NAD C320 not turning ON

[jmascreen]

My NAD C320 integrated amp stopped working today. There are now output to speakers, it does "power Up" but in seconds it turns Red from green. Although all other lights working as expected but there is no sound coming from speakers. I have disconnected all inputs and speaker cables as well.

Any input or pointers to resolve this is problem is highly appreciated,

 

[GeorgeO]

On the face of it , there could be a problem with the power supply, worth taking it to the local NAS dealer or a even better, a competent local techie and tracing where the power supply has stopped.

 

[jmascreen]

Thanks George.
I had kept it disconnected from yesterday night till today evening and tried to connect it again, and it worked around 5 minutes and again turned red. Very strange situation..

Well does anyone know a good technician in PUNE who can fix it?

 

[zeds]

On the face of it , there could be a problem with the power supply, worth taking it to the local NAS dealer or a even better, a competent local techie and tracing where the power supply has stopped.

are you sure?

 

[thampi]

i think its relay is switching off itself.must be a short circuit or a faulty relay

 

[jmascreen]

i think its relay is switching off itself.must be a short circuit or a faulty relay

How do i check it?

 

[GeorgeO]

You need to get a reasonably competent person to trace the electrical path using a DMM.

 

[reubensm]

Hi, the problem you are facing is one that commonly effects the C320, C320 BEE, and all other NAD amps in the C-xxx series and C-xxx BEE series. When a NAD amp plays for some time and switches to stand by, its got to be capacitor failure somewhere or its got to be a thermal shut down. If you amp never turns on and remains in stand by then it could be power supply filter capacitor failure, output transistor failure causing short circuit, relay failure, etc.

In your case, since the amp sings for some time (briefly) and then shuts off, I am sure there is a capacitor somewhere (probably used across the power rails in the preamp and poweramp sections for filtering) has given way and is causing a short circuit.

In the past my brother has fixed this issue on a C320BEE, after some checking, he found a resistor blown (it had blacked out). He replaced the resistor, the amp worked ok for some time, before the resistor over heated and blew again. He then did some further investigations and noted that a capacitor in the preamp stage was shorting. On replacing this capacitor, and the resistor, the resistor stopped heating up and the amp worked perfectly well ever since. If I remember correctly, the capacitor was C68 in the preamp section and the resistor was R45 (not sure if I recall these correctly). Please refer to the c320bee schematics to locate these and then refer to the C320 schematics to find the same components. Incidentally my brother owns the C320 himself and services it by himself.

If you are not very familiar with amplifier circuitry and servicing. Suggest you hand over the amp for repairs, to a qualified technician.

 

[jmascreen]

Thanks all for the suggestion, I will get this fixed from a qualified technician..
Need to find one in PUNE..

 

[ojiangenp]

You need to get a reasonably competent person to trace the electrical path using a DMM.

 

[Robert Bose]

I feel the problem is DC in the output to speakers
Most amps have a protection circuit which disables the speakers
thru a relay contact, if there is more than 50-100 mv DC on the output
to speakers, to protect your speakers
there would be an offset trim pot, and also a bias current trim pot
during the 5 minutes it works before it shuts down, connect a
multimeter across the speaker + Ve and -Ve output, without ant speaker
or input connected and measure the DC millivolt out,
if it is more than 50-100 mv ( Normally 20 mv ) the offset adjustment
may need trimming, I dont think power Transistor or Power Supply filter
may have shorted as this would result in fuse blowing
and then it wont turn on even for few minutes after switch on, listen for
click sound of relay activation after switch on

Robert Bose

 

[omishra]

I opened this Amp in front of OP. It has all PS caps leaked. Big ones (2 X 15000F,50V) are making noise from inside when shaken, for sure aluminum can has dried from inside. Others caps are swollen. Its relay is working and supply lines are around prescribed limit. Initial output offset is 25mV and bias current is okay.
It seems due to impure PS, bias changes and it heats up after some time. This causes thermal shutdown after some time. Parts are purchased by owner from element 14 and pending arrival.

 

[reubensm]

I opened this Amp in front of OP. It has all PS caps leaked. Big ones (2 X 15000F,50V) are making noise from inside when shaken, for sure aluminum can has dried from inside. Others caps are swollen. Its relay is working and supply lines are around prescribed limit. Initial output offset is 25mV and bias current is okay.
It seems due to impure PS, bias changes and it heats up after some time. This causes thermal shutdown after some time. Parts are purchased by owner from element 14 and pending arrival.

Great going, good thing about NAD amps is that they are the easiest to fix :yahoo:

 

[jmascreen]

I opened this Amp in front of OP. It has all PS caps leaked. Big ones (2 X 15000F,50V) are making noise from inside when shaken, for sure aluminum can has dried from inside. Others caps are swollen. Its relay is working and supply lines are around prescribed limit. Initial output offset is 25mV and bias current is okay.
It seems due to impure PS, bias changes and it heats up after some time. This causes thermal shutdown after some time. Parts are purchased by owner from element 14 and pending arrival.

Thanks OM.
Here is the culprits

 

[jmascreen]

Where do I get the voltage ratings for primary and secondary for toroidal transformer?

 

[jmascreen]

Where do I get the voltage ratings for primary and secondary for toroidal transformer?

Any help if someone can measure it for me will be really appreciated


Sent from my Moto G (4) using Tapatalk

 

[jmascreen]

Updates

After a failed attempt with local technician who had troubleshoot it as failed toro transformer and got it rewound to a specific value (I got it rewound from Toro Trans Pune, who did an amazing job). The technician assured that he had fixed the issue and returned the amp. At my home it played again for 30 minutes and went back to protection mode, and the tech fellow had started giving statements like it could be issues with my speakers or other associated devices. So I thought to skip this fellow and move on and put the Amp in R.I.P status.

After two years around last Diwali I was planning a trip to Kerala, so just thought to get this repaired over there. Since I don’t have any idea about technician and don’t want to take a chance I dropped a PM to FM reubensm for reference for any good fellows. And to my surprise he reverted that he can fix my NAD 320 issue, so I have dropped the amplifier at Reuben’s place at Thiruvananthapuram.

Despite having a hectic schedule, Reuben used to find time to check the amp, found all the failed components and replaced it. He also kept me updated status each day like a day scrum. Rather than doing a simple fixes to solve the issue, he had restored the amp to original NAD specifications by replacing non matching components where some components were working abruptly.

After the restore job and rigorous testing, amp was returned me last week. I have connected it to my previous chain and started listening CD after CD. After each CD passed the sound has become really amazing and very musical also found a day and night difference comparing how it worked earlier and now

Before ending the post, I would like to thank FM Reubensm for all the efforts he put in to restore the NAD C320 as original it can be.
And can’t be ended without thanking FM omishra for all the help and guidance provided.

My joy has kept on increasing songs after songs​

 

[reubensm]

Actually I would like to thank FM Jmascreen for giving me an opportunity to repair his amplifier. It was really a fun experience, especially with troubleshooting. I had a number of projects at hand and somehow managed to find the time to complete the task, which took over 2 months.

Edit: The art of amplifier repair can be better explained with the definitions of repair vs restoration. If the amp is new and untouched, repairs will solve most problems, however if the amp is older, worked on previously or modified, restoration is the only complete end solution. This also reminds me of an old saying - the harder the effort, the sweeter the fruit

Wish you many many years of enjoyable listening on your lovely NAD C320

 

[efernand1]

Excellent experience shared and hats off to Reubensm who went the extra mile in resolving FM challenge....a true example of collaboration and trust!

 

[jmascreen]

Just wanted to add some details about the changes incorporated.

changed couple of thyristor, Relay & Op amp in protection circuit along with some caps which were not matching to factory specifications @reubensm please add if I missed anything so if someone searches for similar issue can refer.

Coming to output sound quality the NAD is driving very easily driving my 8 ohms 84db TL Speakers which F5T found hard to drive. Never felt this tight bass when I was using it @2014. The best is how the music flows.

Come February this will be my main system.