johnhoef
Well-Known Member
Hello, everyone,
I just scanned through all the threads concerning this NAD C356BEE, and see very little about repairs. This must be quite a reliable amp! Well, this one I am working on does indeed, have a problem. Thought I might start a discussion about this particular problem I am having, concerning a rather unusual design in the power supply. Referring to page 17 of the service manual, the upper right corner is the "SUPPLY CIR", as it is labeled. This circuit provides the plus and minus 26 voltages, the plus and minus 18 voltages, and the plus 12 volts. An unusual design utilizing a device called an adjustable shunt regulator, part number AZ431. This is the first time I have seen this device. With no explanations in the manual, I am left to figure out how this power supply works. My first thought is - why this design, when a simple three terminal IC regulator would work just fine? Like the regulators that they use to develop the plus and minus 18 volts. So, the malfunction is within the circuit that uses Q41, Q43, and this IC301 which is the AZ431. R413 was burned, so I replaced that. Figuring the AZ431 would have been stressed, I decided to replace it as well. My local supplier did not stock these, but he did have an ECG999M. This is an 8 pin DIP style IC. Not exactly what I had in mind to use, but it was quite cheap, so I decided to use it. It took some creative wiring to get it in the circuit, but got it done. Still the supply does not work. As I bring up the variac, the output of this circuit goes past 26 volts. Have any of you looked at this circuit before? Any thoughts?
I just scanned through all the threads concerning this NAD C356BEE, and see very little about repairs. This must be quite a reliable amp! Well, this one I am working on does indeed, have a problem. Thought I might start a discussion about this particular problem I am having, concerning a rather unusual design in the power supply. Referring to page 17 of the service manual, the upper right corner is the "SUPPLY CIR", as it is labeled. This circuit provides the plus and minus 26 voltages, the plus and minus 18 voltages, and the plus 12 volts. An unusual design utilizing a device called an adjustable shunt regulator, part number AZ431. This is the first time I have seen this device. With no explanations in the manual, I am left to figure out how this power supply works. My first thought is - why this design, when a simple three terminal IC regulator would work just fine? Like the regulators that they use to develop the plus and minus 18 volts. So, the malfunction is within the circuit that uses Q41, Q43, and this IC301 which is the AZ431. R413 was burned, so I replaced that. Figuring the AZ431 would have been stressed, I decided to replace it as well. My local supplier did not stock these, but he did have an ECG999M. This is an 8 pin DIP style IC. Not exactly what I had in mind to use, but it was quite cheap, so I decided to use it. It took some creative wiring to get it in the circuit, but got it done. Still the supply does not work. As I bring up the variac, the output of this circuit goes past 26 volts. Have any of you looked at this circuit before? Any thoughts?
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