Charles Wm. Edwards wrote:
I was listening to the unit one night when all of a sudden the sound cut
out. The front panel LEDs still work. After opening the unit I found all
four line in fuses blown. (2) 4 amp and (5) amp fuses. Bought new fuses
and installed thinking a surge in the incoming house power could have
been the cause. As soon as I turned the unit on the new fuses instantly
blew. Can anyone give me an idea as to what could be happening. Thanks.




Hello,


These fuses (all of which are 'T' type) are on the power amp
transformer rails. It is almost certain that either a pair of output
transistors, 'power envelope' transistors, or more have blown. Usually
only one channel fails. If an output is bad, I'd suggest replacing both
outputs, the driver transistors and the bias transistor at the same
time, and use original devices, though a 2SD669 is a good sub for the
bias device.

If the 'power envelope' transistors have failed, use the BD911 and
BD912 transistors that NAD used on later production, NOT the 2SA... and
2SC... ones the early units had. Bias and offset adjustments must be
made after repair, or it will soon fail again.

Regards,
Tim Schwartz
Bristol Electronics