Hi all,
I am trying to repair a NAD C352 amp. The symptoms are that it powers on to an orange standby LED, and when you try to power it up, the relay on the power board clicks but nothing else happened.
I originally thought it was due to dead caps on the power board (they're notorious for this) but I later also determined that there is a shorted diode on the power board in the rectifier circuit, and also that the transformer itself is completely dead. I have determined this by measuring continuity on the primary and there's nothing. Completely open. And when you power it up, no voltage whatsoever on the secondaries.
I am trying to see if I can find a suitable replacement transformer but I am struggling to work out what voltage I need.
Can anyone have a look through the service manual and help me out?
https://elektrotanya.com/nad_c352_sch.pdf/download.html
Many thanks!
I am trying to repair a NAD C352 amp. The symptoms are that it powers on to an orange standby LED, and when you try to power it up, the relay on the power board clicks but nothing else happened.
I originally thought it was due to dead caps on the power board (they're notorious for this) but I later also determined that there is a shorted diode on the power board in the rectifier circuit, and also that the transformer itself is completely dead. I have determined this by measuring continuity on the primary and there's nothing. Completely open. And when you power it up, no voltage whatsoever on the secondaries.
I am trying to see if I can find a suitable replacement transformer but I am struggling to work out what voltage I need.
Can anyone have a look through the service manual and help me out?
https://elektrotanya.com/nad_c352_sch.pdf/download.html
Many thanks!
I think this is one of the NAD's with a standby transformer, which needs to activate for power to be supplied to them main transformer.
Check the caps, C401 etc and IC401 and BR401 to make sure you are getting the 5v that triggers everything else, including the real of the main transformer
Check the caps, C401 etc and IC401 and BR401 to make sure you are getting the 5v that triggers everything else, including the real of the main transformer
Most likely the transformer has a thermal fuse embedded in the winding and that has failed open circuit.
I doubt you will find one. The transformer has windings with tapping's to give the 'normal' supply to the amp along with the additional higher voltage supply that gets switched into circuit when needed.
The diagram is confusing and little information is present but I suspect the supplies are -/+37 volts (normal) and -/+50 volts (high) which would equate to a transformer with a winding of 35-26-0-26-35 volt AC.
I'll just add that these switched rail designs so beloved of NAD are often a problem. You likely could just run it on a normal supply and forget the higher rail feature. I doubt it would have any impact on the subjective maximum levels the amp could deliver given that mostly we listen to just a watt or two.
-/+37 volts dc is good for a 50 to 60 wrms amp.
-/+37 volts dc is good for a 50 to 60 wrms amp.
Interesting. How does that work exactly? Does the power supply do the switching?
Do we think a 2x50V transformer would work on its own as @Mooly said above?
Thanks everyone. It'd certainly be great to get the amp up and running again even if it's not quite to factory spec.
That's not what I'm saying 🙂
If you actually used a 2x 50 volt transformer you would end up with 50*1.4 = -/+70 volt rails. The rectified DC value is approx 1.4X the AC value.
The only clues I can see on the diagrams are these. The 50 volt marking I would assume is the 'high' level. The 37 volt value sounds more like the 'low or normal' rail value.
Th high voltage supply is superimposed over the low supply when the amp output reaches higher levels.
From a different amp but showing hgow it works.
Sorry I was more referring to you saying a normal power supply would work 🙂
Are you able to suggest a transformer that would work? 2x26-30v ish V?
Are you able to suggest a transformer that would work? 2x26-30v ish V?
I think it would work. Also remember transformer specs are at max secondary current and voltages rise at light loading as a 25-0-25 seems most suitable.
Thanks Mooly. Appreciate your help. I'll come back to this thread if I decide to grab another transformer and give it a go versus just chucking it back on eBay.
In terms of wiring it in, would I connect the 25v secondaries to both the normal and the "higher power" inputs to the power supply from the toroidal?
In terms of wiring it in, would I connect the 25v secondaries to both the normal and the "higher power" inputs to the power supply from the toroidal?
