NAD 7240 PE "Idle current" adjustment procedure assistance/clarification

Discussion in 'The Projects Forum' started by MEB13, Mar 27, 2012.

  1. MEB13

    Thread Starter New Member

    Aug 16, 2011
    Yesterday, 05:05 PM
    Hello all,
    I'm currently working on the finishing touches to an NAD 7240 PE receiver and during the "Main Amplifier Alignment"
    procedures I've run into a problem during the "Idle current adjustment" procedure as described in the service manual.
    The problem is, well first maybe I should show what the manual describes as the procedure in question. It's pretty short so:

    B. Idle Current Adjustment. (A. was "Center Voltage Adjustment")

    1.Remove solder short across R-471 and R-472
    2.Connect DVM across R-471
    3.Turn on and adjust VR403 for a reading of 28mV +/- 2mVDC.
    4.Repeat using R-472, adjust VR 404.

    C. Final Adjustment
    1.Leave power on a minimum of 5 minutes.
    2. Repeat Center current (A) and Idle current (B) adjustments.
    3. When finished replace solder shorts across R-471 and R-472

    ...and that's that.
    The problem is:
    There are NO SOLDER SHORTS ACROSS R-471 and R-472!
    And no other shorting method that I can see that might accomplish the same thing. (A) the center current adjustment went just fine
    but now I'm stuck at (B) the Idle current adjustment because I have no idea what to do at this point.
    Should R-471/2 which were not shorted when I received the receiver, be shorted to accomplish the "Idle current adjustment?(..and shorted how?)
    And once this question is answered should the solder shorts be "replaced" as instructed in the last step (C-3) when they didn't exist in the first place?!!
    I'd really appreciate any input anyone has to give on this. This is weirding me out, seriously.
    The unit was blowing fuses left and right and I noticed that two of the output trans were shot.
    So I replaced all 4 and hooked it up to a "current limiter" and all seems quite well, to make a long story short.
    But these adjustments are holding me up and I can't just neglect them.
    So any help on this issue would be appreciated. I have the service manual with schematics and block diagrams for anyone that'd like them.
    Thanks to all,
  2. MEB13

    Thread Starter New Member

    Aug 16, 2011
    This is the rest of the schematic images (top left / top right)
    I also have pics of the pc board and the resistors in question if anyone would like them as well.
    I'm very grateful to anyone that can give me their opinion on this issue.