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Old 14th July 2006, 10:47 PM   #1
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Default NAD 705 Troubleshooting

All:

I just got a down-and-out NAD 705 receiver. The origanal owner had given up.

I'm new to this, thanks in advance for the advice.... I have to replace the lamps, that was easy enough to find. The protection circuit seems to work, unit powers up. I hear the output relays working. Once I figured out the input selector w/o help of the backlight lamps, I had a working receiver.

Problem: One channel is quieter than the other. I tested between A and B outputs, same result. Duh. I tested AUX and CD, same result. Now, I crossed the pre-outs and in and I got the quiet channel to switch sides. Hmmmm. That tells me I am looking for something messed up in the pre-amp. ????. What device in the preamp would cause all inputs to be quiet on one side? I can't see anything burned up or broken off hand. Not that I would expect, it works but has a gain screwed up or something. Any recommendations?

Thanks again. I AM looking for a good read on the subject....

Also, DC output on the amp channels read 20 mV and 40 mV. I have not tested putting another preamp OUT into the IN of the power amp section. I guess that would verify function of the power amps.

The various preamp level adjustments seem to be clean and functional. Moving them did not cause any level variations or indicate a problem.

jocko
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Old 14th July 2006, 10:51 PM   #2
anatech is offline anatech  Canada
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Hi Jocko,
On some of these units they use a soft clipping circuit. It can cause trouble easily.

Try a "Y" plug from the pre out into the power amp input so you have a true mono signal. Is there still a level difference?

-Chris

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Old 15th July 2006, 06:07 PM   #3
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schematic diagrams??? have you a af generator and oscilloscope?
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Old 15th July 2006, 06:19 PM   #4
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Default Re: NAD 705 Troubleshooting

Quote:
Originally posted by jocko_nc
I have not tested putting another preamp OUT into the IN of the power amp section. I guess that would verify function of the power amps.
Just take away bridge pins from pre-power plugs and connect phono cables in cross to verify if it's pre or powerstage level mismatch.
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Old 15th July 2006, 06:29 PM   #5
anatech is offline anatech  Canada
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Hi claudiomas,
Quote:
schematic diagrams??? have you a af generator and oscilloscope?
Who?
I have the equipment, but no schematic for this one or unit. I do remember the tough troubleshooting on a similar model.

-Chris
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Old 15th July 2006, 06:50 PM   #6
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Quote:
Originally posted by 4fun


Just take away bridge pins from pre-power plugs and connect phono cables in cross to verify if it's pre or powerstage level mismatch.
Sorry for my post, as i have not obviously not read your initial post carefully enough
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Old 15th July 2006, 08:23 PM   #7
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preamps means lots of switchs and pots . 1rst clean and lubricate thems 2 renew soldering mainly on hot and eavey components. then whith Y connector to both preamps inputs 630/1Khz 0db compare whit your oscilloscope to find the trouble .
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