Last measuring.
+-50v.......+54v.......-54v
5.6v........5.6v
Trigger out 12v........26v
+18v.........+14v
-18v ..........+0.5v
12v...........8.4v
Amplifier power on.
With headphones no protect mode
Without headphones protect mode
With original r245 33 ohm resistor.....
Mystery....
The sound on headphones is very low and distorted
+-50v.......+54v.......-54v
5.6v........5.6v
Trigger out 12v........26v
+18v.........+14v
-18v ..........+0.5v
12v...........8.4v
Amplifier power on.
With headphones no protect mode
Without headphones protect mode
With original r245 33 ohm resistor.....
Mystery....
The sound on headphones is very low and distorted
Last edited:
First, main power supply, BR402&BR403/P405B's output voltages must be equal and 50V. You have to solve that. After, then you can solve other problems. It has talked about before.
And there are dangerous voltage, be carefull.
And there are dangerous voltage, be carefull.
Now, I opened the NAD and I measured the P405B output voltage. Output voltage not 50V, it's 43.2 volts (43.0-43.5 volts, P101B connected or not, power amp. opened or not). 0.1,0.2v difference between polars.
(I remember that BR402&BR403 voltages different. So, when C352 is running main voltage (P405B) changing. When you reading schematic this may help you).
(I remember that BR402&BR403 voltages different. So, when C352 is running main voltage (P405B) changing. When you reading schematic this may help you).
1) the +54v, -54v are measured with the P102B not plug in, correct?
2) there is two 12v supply, one is independent regulator Q163 via J302.
3) the other 12v supply is R251, Q159, Q160, controlled by R254, R255.
to maintain steady 12v, the +18v must be ok, otherwise the -18v also won't appear.
4) which 12v became 26v, and which became 8.4v.
5) if 12v became 26v, the output transistor must be in trouble,
6) if 12v became 8.4v, the supply current before the output transistor must have a short that can not provide sufficient current to maintain 12v or the output transistors are in trouble.
7) headphone output is directly connect to amp out via a resistor, as the +-18v not normal, the input diff. stage would not work properly, you can only hear distorted sound.
******
don't just ask questions,
the amp is in front of you while members only know it by your description.
members need your clear description of you amp...otherwise we know nothing about it,
without helpful data about the amp, we can only guess that I don't want anymore.
*****
should you post a clear photo inside the amp.
how are the ac voltages measured.
*******
hope you fix it soon.
2) there is two 12v supply, one is independent regulator Q163 via J302.
3) the other 12v supply is R251, Q159, Q160, controlled by R254, R255.
to maintain steady 12v, the +18v must be ok, otherwise the -18v also won't appear.
4) which 12v became 26v, and which became 8.4v.
5) if 12v became 26v, the output transistor must be in trouble,
6) if 12v became 8.4v, the supply current before the output transistor must have a short that can not provide sufficient current to maintain 12v or the output transistors are in trouble.
7) headphone output is directly connect to amp out via a resistor, as the +-18v not normal, the input diff. stage would not work properly, you can only hear distorted sound.
******
don't just ask questions,
the amp is in front of you while members only know it by your description.
members need your clear description of you amp...otherwise we know nothing about it,
without helpful data about the amp, we can only guess that I don't want anymore.
*****
should you post a clear photo inside the amp.
how are the ac voltages measured.
*******
hope you fix it soon.
I replaced D119.
He was no bad but no zener, someone soldered the usual 4148.
And now +18v & +12v are ok.
All led on front panel are workings
It rest to solve'problem of -18v......
He was no bad but no zener, someone soldered the usual 4148.
And now +18v & +12v are ok.
All led on front panel are workings
It rest to solve'problem of -18v......
Last edited:
Zener, zener, zener 
(one more measurement; when amplifier running, P102B connected, voltage 52volts).
(one more measurement; when amplifier running, P102B connected, voltage 52volts).
I think you installed preamplificators? If so, after high voltage preamp. transistors may burn.