"David Farber" wrote in message
...
This NAD 2240PE had nine bad transistors replaced on one channel and I was
wondering if anyone had knowledge of the bias test points. This set does
not
seem to use the normal 5 watt emitter resistors to check the bias current.
It's operating fine as is but I'd like to see if it's within spec.

Thanks for your reply.

--
David Farber
David Farber's Service Center
L.A., CA


I don't have any specific knowledge of this particular amp's bias set up,
but usually, if I find myself in that situation, I look for some way of
measuring a comparison voltage with the channel that wasn't worked on, which
is, as you say, usually the voltage across the emitter resistors, if it has
them. I've also often found that there are bridged out test points, where
you can break in with an ammeter to measure the idle current, which is rule
of thumb typically 20mA. If all else fails, the temperature that the output
transistors run at on the rebuilt channel, compared to those on the other
channel, is usually a pretty good guide as to how evenly the two channels
are running with respect to one another. This should be checked with the amp
just idling. If the rebuilt channel gets hotter than the ok channel quite
quickly, then the chances are that the bias is set too high. If the rebuilt
channel is still stone cold after 15 mins, and the ok channel is just warm,
then the bias is too low. As a final check, sometimes you can see the
crossover distortion on a sine wave, when the bias is set wrong.

Arfa