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AAVAudio Guest
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Posted: Mon Mar 26, 2012 8:45 pm Post subject: NAD 7240 Amplifier Idle current adjustment question/clarific |
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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 really 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,
AAVA |
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Tue Mar 27, 2012 12:20 am Post subject: |
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Schematic shows a jumper across resistors. To find out for sure, remove one resistor and check resistance reading at the solder "pads" with a DVM. A zero reading means there IS a jumper still there whether you see it or not. _________________ You're over there, I'm over here. |
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Justmanuals
Joined: 21 Aug 2004 Posts: 1948
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jts1957
Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away
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Posted: Tue Mar 27, 2012 12:45 am Post subject: |
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Guess you didn't read far enough, Paul?
AAVAudio wrote: | I have the service manual with schematics and block diagrams for anyone that'd like them. | _________________ You're over there, I'm over here. |
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Justmanuals
Joined: 21 Aug 2004 Posts: 1948
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