I have a NAD C740 stereo receiver (https://www.hifiengine.com/manual_library/nad/c740.shtml) that worked fine for many years, and is now non-functional. I'm trying to figure out what is wrong, in the hopes that I can fix it. I'm a beginner when it comes to repairing audio equipment, but I know basic electronics and can solder etc.
This receiver has an on/off power button on the front panel. The usual behaviour is that powering on using this button puts the receiver in a standby mode (indicated with a green LED), after which selecting a function (e.g., AUX, CD, FM, etc.) fully turns on the receiver into that function.
However, after a week or so of intermittent function in which the receiver would power on normally and then "shut itself down" as it were, it now won't power on at all. The on/off button does not light the LED and pressing the function buttons does nothing.
My first thoughts were that this could be a relay or capacitor issue. But I've opened up the cover, and nothing is obviously amiss (no bulging capacitors or anything).
The service manual for this receiver has some block diagrams and schematics, but no test points or anything like that.
As a first pass, would it be worthwhile just to replace all the large electrolytic capacitors with new ones ("name brand"?) of the same (or higher) voltage rating and higher capacitance? How likely is this to be a cap issue vs. a relay issue?
Any advice would be appreciated. Thank you in advance.
This receiver has an on/off power button on the front panel. The usual behaviour is that powering on using this button puts the receiver in a standby mode (indicated with a green LED), after which selecting a function (e.g., AUX, CD, FM, etc.) fully turns on the receiver into that function.
However, after a week or so of intermittent function in which the receiver would power on normally and then "shut itself down" as it were, it now won't power on at all. The on/off button does not light the LED and pressing the function buttons does nothing.
My first thoughts were that this could be a relay or capacitor issue. But I've opened up the cover, and nothing is obviously amiss (no bulging capacitors or anything).
The service manual for this receiver has some block diagrams and schematics, but no test points or anything like that.
As a first pass, would it be worthwhile just to replace all the large electrolytic capacitors with new ones ("name brand"?) of the same (or higher) voltage rating and higher capacitance? How likely is this to be a cap issue vs. a relay issue?
Any advice would be appreciated. Thank you in advance.
Hey Joe_Q I have repaired a NAD C 320 which might be similiar to the C740. I found one 2300uf cap which was dried up but the 7805 it supported still worked. The 38vdc needs to be regulated down to 18vdc. Look for a 33ohm fusable resistor in that circuit. The 18vdc is for the preamp circuits and is not turned on until you select an input channel. I am guessing that capacitors are not a root cause of failure.