NAD C370 power-on problem

[windfall123]

I am having problems with power-on cycle on my NAD C370 amp. The delay between power-on and deactivation of protection (the moment when the amp unmutes sound and amber LED turns green) increased to 3-5 minutes. After that, amp seems to be working fine. The problem does not affect the sound.

My questions are:

1. Where can I get schematics for protection circuitry? I saw power amp schematics on this board, but it did not include protection curcuits.

2. Any recommendations on where to look for problem first? I must admit I am not very experienced in DIY electronics, but I have basic skills and know how to use multimeter. I feel I would be able to repair the amp... if only I knew what exactly is wrong with it.

Thanks in advance for any help.

Andrei

[derguteton]

look at this

http://www.diyaudio.com/forums/showthread/t-97892.html

...and search for it at: http://fileshare.eshop.bg

you will find a schem "with" the protection circuit.


greetings from Berlin Michael

[cyteen]

A bit late but may help someone:

[windfall123]

Thanks for the post, this is very helpful!

Andrei

[Telnet100]

Hello!
As I do work for a NAD Dealer, this might help:

Your problem is probably due to The Electrolytic Capacitors on the Speaker Protect Board - (you are in the right place)!

These Electros get overheated by heat from the Zener diode, which is mounted at the top of the Pcb, and they then dry up, losing their value.
My fix: To replace all these electros, and remove the Zener Diode from the front/top of the Pcb, then resolder it back onto the back/
bottom of the board, so letting it's heat go elsewhere.
(make sure of it's correct polarity).
In our Opinion, this is a VERY bad design point of the C370, as it
has the effect of a built-in 'time bomb', and the Amp will eventually fail no go. I can't see why NAD would have done this.
I have now repaired several the same, and this works really well.
Hope this helps You!
Regards, Telnet.

[windfall123]

Hi Telnet -

Thanks for the tip, I have been able to repair the amp successfully. You were right on point - the problem was caused by fried capacitors on protection board. Replacing caps C783, C784, C785 worked like charm.

Andrei

[jwh]

Thanks to all above. Have just replaced the 3 capacitors described, which has cured my C370 start up delay problem. I didn't move the Zener, should have really, but it was at least 12mm above the capacitors.

I was disappointed that when I rang the local Nad dealer, they said they could cure the problem, which they had not heard of and they didn't have any service manuals or schematics. Estmated repair cost, £80-£100!!

Thanks again.

John

[turbonezze]

Hello, I have the same problem with my NAD c370, but I must be blind becuse I can't find the Speaker Protection Board in my reciver. Can anybody please help me where to find it.