Troubleshooting NAD C350

[RobHance]

I am having a problem with my NAD C350. Upon power-up the green power light turns on and then fades to red as the protection circuit kicks in. I have inspected the boards and nothing looks obviously blown. All the fuses are good and the power supply is outputting its +/- 40 volts properly. I am not sure what to check next.

I have searched here and other places on the web and have read about many other people encountering similar issues but I have yet to read a solution to the problem. If anyone has a suggestion on what to check next it would be appreciated.

Thanks
Robert

 

[Chrisr3521]

heres the solution

 

[RobHance]

heres the solution

Thanks for the suggestion. I immediatly checked those resistors but it looks like the manufaturer already beat me to it. The two "resistors" were just jumpers anyway. I guess my unit was made after the original problem was found.

Thanks again, you got me very excited for about five minutes!

Robert

 

[Chrisr3521]

i'll have another dig around, i'm pretty sure there was another service bulliten for this amp, another thing to consider is that the output transistors have blown, you can check this by measuring voltage on the relay, high voltage (meaning almost always power supply voltage) means transistors have blown somewhere

 

[RobHance]

That would be great if there was antoher service bulletin. Thanks a lot for checking.

Sorry for the noob question but where is the relay?

Robert

 

[Chrisr3521]

hi, the service bulliten is not for your problem, however i have found somemore, have a good look around eveywhere under a bright light looking for burnt components if you find any i have service information relating to this, the relay should be a plastic rectangular box maybe an inch or so high.

 

[RobHance]

I just measured the relay voltage and it is reading 49V between pins 1 and 4 and also between 8 and 5 according to the pin designation of the specification sheet linked to below. The relay is rated for 24V so I am guessing this is bad. All the other pin combinations read 0V.

http://www.ziming.sh.cn/zm/relay/pdf/gonglvjidianqi/ftr-f1.pdf

I did not see any burnt components or burned places on the boards but I will keep checking.

 

[RobHance]

Update:

Something I did not mention earlier is that this problem is intermittent. That said, I noticed the power light had shifted back to green so I checked the relay voltage again and pins 1 and 4 read 24V while 8 and 5 still read 49V. Referring to your earlier post perhaps the output transistors are blown.

The green light didn't last long. Later in the day it switched back to red and both sides of the relay read 49V.

 

[RobHance]

The current status of the amp is if it is left turned on for a long time the red protection light goes off and the green light comes on, as if the amp does not work until it warms up. If this indicates that the output transisotrs are blown how do I go about checking them? Do I have to remove them from the board?

Thanks,
Robert

 

[Chrisr3521]

i, dont think its the output transistors, it could be the power supply caps, ive had this problem with one of the nad classic series before i think the c320, just have a close look at them look for swelling, leakage check there firmly conected to the circuit board. maybe post a picture if you can.

 

[RobHance]

I'll try to take a couple pictures when I get home tonight. I have not noticed swelling of the capacitors but there is some dark residue at the base of one and on the board around its base. I thought it was just excess glue from installation but maybe it's leakage.

Thanks again for the help. I'll post some pics later.

 

[Chrisr3521]

its most probably glue, but the one i repaired as i said had this fault, and when it arrived through the post the caps had completly come off the board!

 

[Stonecape]

I also have this problem.

For a long time the amplifier worked fine, then when turning on, I get the red light, then after 10-15 mins it turns green again. Now it never turns green.

What should I first check out?

Thanks.

 

[Chrisr3521]

it, could be but this is just a guess, that some caps have dried out due to heat from other components, most probably in the protection circuit. have a look around for a service manual, this should help you more

thanks
chris

 

[lewis71980]

I have a similar problem.
It was doing this for about a week. YouTube - Nad c350 clicking problem

Now today it won't even start. Video here. YouTube - NAD C350 Relay sound keeps clicking will not start up. I opened it up and C507 bulging blue 16v 1000uF C404 C403 Nad cd 293 purple 63v 2200uF x2 bulging.

Does anyone have a service manual I can take a look at, seems fiddly and so many screws holding the thing together.

It's provided 10 years of service so far!!

 

[Chrisr3521]

My advice, replace all caps apart from the big power supply one's with 105oc good quality capacitors. If you pm me your e-mail address and i'll send the manual over.

chris

 

[Loko27]

I have a similar problem too.
On my amp the white relay RL 501 have burned contact.
It's the relay that switch the main power supply on, white plastic with copper
contact.

I want to replace it with a stronger one
So if someone have the service manual it would be very appreciated and useful for the compatibility for new parts.