NAD312 Problem SOLVED
I've modified this thread now that i've found out what's the problem with my NAD. I hope this help others.
i've just bought a Nad 312 with the objective of repairing it.
The problem that was discribed to me was that 'the green light powers up but there's no sound'.
The 4Amp fuses that protect the unregulated part of the power supply were blown. I've found 630mA fuses there and i wonder who put his hands on the amp before me....
I've replaced the fuses and powered the amp. the fuses were ok but i fount around -30V DC on both exits of the amp. After some investigations i've checked that the power supply voltages were all ok.
Checked that the pre section of the amp was working fine also. The problem is with the power section.
Checked that no capacitors were shorted and the joints were all ok.
The voltages on the driver and output transistors were completely crazy with -28v on the bases of the transistors. So what seems to be the problem?
Well NAD (and other manufacturers) use some special resistors in key-parts of their amps. These resistors are recognizable by theys blue-greyish color. These are called fusible resistors and they act as regular resistors but when the current through them is too intense they eat up and eventualy blow. They're covered in a special paint that's non flamable so that this won't cause problems.
That's what happens when the amps are driven too hard or when a power surge happens.
In my amp a resistor of 68ohm was open in the positive supply part. Without that to compensate the negative part of the simmetrical power supply the negative took over the power amp ence the negative output.
Some NAD amps are very prone to this because the fusible resistors were not mounted elevated in the board but close to it so they don't dissipate the eat and eventualy they burn up after some time. If your amp stops working check them out before buying new transistors for your amp.
ADVICE: Never change the fusible resistors with regular ones. they're there to protect the amp and if something goes wrong regular resistors may catch fire instead of breaking the circuit!!!!
I've modified this thread now that i've found out what's the problem with my NAD. I hope this help others.
i've just bought a Nad 312 with the objective of repairing it.
The problem that was discribed to me was that 'the green light powers up but there's no sound'.
The 4Amp fuses that protect the unregulated part of the power supply were blown. I've found 630mA fuses there and i wonder who put his hands on the amp before me....
I've replaced the fuses and powered the amp. the fuses were ok but i fount around -30V DC on both exits of the amp. After some investigations i've checked that the power supply voltages were all ok.
Checked that the pre section of the amp was working fine also. The problem is with the power section.
Checked that no capacitors were shorted and the joints were all ok.
The voltages on the driver and output transistors were completely crazy with -28v on the bases of the transistors. So what seems to be the problem?
Well NAD (and other manufacturers) use some special resistors in key-parts of their amps. These resistors are recognizable by theys blue-greyish color. These are called fusible resistors and they act as regular resistors but when the current through them is too intense they eat up and eventualy blow. They're covered in a special paint that's non flamable so that this won't cause problems.
That's what happens when the amps are driven too hard or when a power surge happens.
In my amp a resistor of 68ohm was open in the positive supply part. Without that to compensate the negative part of the simmetrical power supply the negative took over the power amp ence the negative output.
Some NAD amps are very prone to this because the fusible resistors were not mounted elevated in the board but close to it so they don't dissipate the eat and eventualy they burn up after some time. If your amp stops working check them out before buying new transistors for your amp.
ADVICE: Never change the fusible resistors with regular ones. they're there to protect the amp and if something goes wrong regular resistors may catch fire instead of breaking the circuit!!!!
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Hello All,
I've got problems to my NAD312 amplifier.
I felt that the sound of 2 channels are not the same level.
The amplifier have the U-bridge at backside (pre-out to Main). I am using 1 Khz sine tone generate to Aux and measured the level from pre-out are same to left and right . Then i think pre-out stage is ok.
From the power stage: can someone help me:
What is the correct bias to the R455 (1 Ohm) on the schema?
I measured (the amplifier using 0.1R , not 1R as show on schema), and Left channel is 0.3mVdc, Right channel is 0.6mVdc.
thanks for alls
I've got problems to my NAD312 amplifier.
I felt that the sound of 2 channels are not the same level.
The amplifier have the U-bridge at backside (pre-out to Main). I am using 1 Khz sine tone generate to Aux and measured the level from pre-out are same to left and right . Then i think pre-out stage is ok.
From the power stage: can someone help me:
What is the correct bias to the R455 (1 Ohm) on the schema?
I measured (the amplifier using 0.1R , not 1R as show on schema), and Left channel is 0.3mVdc, Right channel is 0.6mVdc.
thanks for alls