NAD 320 BEE - from one to next

[mauric]

Hello Members
I'am now a Week to work on my NAD 320 BEE amp, a replaced meny Caps, the
installed was ancient and broken, also the Relay was damaged. Now the amp
are the first time up (from his Protect mode), but the defective shafts continues.

and now I'm amazed, because I marked a coule day this resistor R068 3W as ok,
but now this four pieces are burned  , and only this, if messure the other
participants in the area around the "railway" this seem to be ok ?

please iam not a expert ... but I would bet that if I replace these 4 resistors the
next faulty will appair .... please how i can or.. please can somehow prevent
such domino effects like this?

The Power are running 48+ and - the Fuse are fine. the initial error was a amp
that don't come out from protect mode.

Thanks for discuss this
Regards
Mauri

[coromonadalix]

hifiengine has your service manual, registration is free  it will help you

[mauric]

Thx, Yes i'am Member since 3 years and 15 weeks ;-)

[Twoflower]

Is the meter actually in Resistor mode? I see a V and probably DC in the display...

[SpecialK]

When you say "resistor R068 3W as ok, but now this four pieces are burned "  do you mean:

1 - R068(not marked on schematic) broke into four pieces
2 - All four 0.068 ohm resistors are visibly burned up?
3 - All four 0.068 ohm resistors report as dead shorts?
4 - All four 0.068 ohm resistors report as open circuit on ohmeter?

I don't think you can measure a 0.068 ohm resistor without using a four wire multimeter.  Lead resistance would be greater than load resistance.

[Le_Bassiste]

Is the meter actually in Resistor mode? I see a V and probably DC in the display...

yup, seems to be the case
also, those resistors' fault mode is usually "open", but not "shorted"

[Le_Bassiste]

When you say "resistor R068 3W as ok, but now this four pieces are burned "  do you mean:

1 - R068(not marked on schematic) broke into four pieces
2 - All four 0.068 ohm resistors are visibly burned up?
3 - All four 0.068 ohm resistors report as dead shorts?
4 - All four 0.068 ohm resistors report as open circuit on ohmeter?

I don't think you can measure a 0.068 ohm resistor without using a four wire multimeter.  Lead resistance would be greater than load resistance.

actually, you can. just short the probe wires and take a note of the resistance. then, take your measurement on the R068 and subtract the resistance value that you have noted before.
any result greater than zero would tell you that the resistor is most likely ok.

[mauric]

Thanks for so meny Answer that i receive!!
Yes and sorry this was my Mistake!! if running the Multimeter in Resistance-mode i have a resistore value from 0.3-0.4Ohm

I mount everything in the case, Power on, put the Sinus to Chinc, No Sound appair, appair little brum on both speakers.
Knocking on the transistors with a hard object, but hum does not change.

the Amp are now still running, the temperature it's in my opinion not critical!
thanks for possible update or input!

[mauric]

I measured the following points earlier. I don't know exactly how to continue here. Please help
Still no sound, and little hum on both Speaker.

[SpecialK]

Check R445 and R446 as they are the sense for the protection circuit.

Also check D419 and D420 as they seem to be the in the feedback mechanism for the soft-clip circuit.

[mauric]

R445 and R446 check, are still Ok
D419 and D420 check, are still Ok

Sorry still measure..... but seems to ok.... 

Still no sound .....

[SpecialK]

Jumpers between pre-out and main-in?