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 Post subject: NAD 7240PE AM freq range
PostPosted: Dec Thu 14, 2017 5:16 pm 
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Joined: Dec Thu 14, 2017 5:08 pm
Posts: 5
Location: Toronto, ON
Hi,

I have the Canadian model (NA model) of the NAD 7240PE. I recently took it out of storage and tried to tune into 1690kHZ, but the upper limit it can tune to is 1610kHz. I thought the upper 1610khz was limit was for the UK/European models and 1710kHz was for NA models. I checked the owner's manual and it mentions nothing about what the AM freq range is. I also looked at the service manual, but that was no help either.

When I used this receiver back in the day, I only used the FM, so I never really bothered to check AM.

Is there an undocumented way to have the receiver extend the AM range? If not, I get the impression that NAD offered only one AM frequency for both N.A. and UK/Europe.

Regards and thanks,
Gus


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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Fri 15, 2017 1:23 am 
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Joined: Dec Wed 16, 2015 10:31 pm
Posts: 203
Location: Toronto ON
Hi Gus, and welcome to the forum.

It was only fairly recently (early 90's) that the AM band was extended from 1610 to 1700 kHz, and your receiver dates back to the mid-80's.
If the tuner were analog, it would probably be possible to extend the range with some careful alignment - it might cause the dial to be a bit off, but not too badly. It would also depend on how much extra 'play' there was at the top of the dial. However, with the band limits 'hard coded' into the circuitry, I would not be too hopeful that there is any way to extend the frequency range.
Perhaps if you were willing to sacrifice from 530 to 630 (and remember that everything is 100kHz off), it may be possible to 'skew' the tuning downward, but without seeing the service manual, I'm not even sure that is a possibility.

Joe


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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Fri 15, 2017 2:18 am 
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Joined: Dec Thu 14, 2017 5:08 pm
Posts: 5
Location: Toronto, ON
Joe,

Thanks for taking the time to reply to my question. Yes, I was afraid that would be the case.
Nevertheless, I extracted from the service manual the AM alignment instructions and tuner alignment points in a pdf file.
If you have an opportunity, please review and let me know if it is possible and potential drawbacks (if any).

If there is some other portion of the service manual that you want me to upload, just let me know.

Btw, hello from Mississauga.

Regards,
Gus


Attachments:
7240PE_AM_adjust.pdf [222.91 KiB]
Downloaded 40 times


Last edited by dieselgg on Dec Fri 15, 2017 2:31 am, edited 1 time in total.
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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Fri 15, 2017 2:27 am 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 7138
Location: Ohio 45177
I see it has VC2 to adjust the synth. frequency. Probably just adjusts the crystal reference frequency. That would be a very small range of adjustment, presumably. So it appears that you are stuck within the design parameters. The alignment is for the tuning Voltage, which presumably uses that Voltage to tune the RF tuning diodes, thus maintaining sensitivity across the band.


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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Fri 15, 2017 2:35 am 
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Joined: Dec Thu 14, 2017 5:08 pm
Posts: 5
Location: Toronto, ON
Thanks for your feedback Joe.

A friend of mine has the 7225PE model and he can tune into 1690. I guess he bought his sometime in the 90s as you had indicated.

Regards and thanks,
Gus


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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Sat 16, 2017 3:54 am 
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Joined: Dec Wed 16, 2015 10:31 pm
Posts: 203
Location: Toronto ON
Although the AM receiver IC and associated components are certainly capable of tuning to the extended range, the controller IC as I feared has its limits 'hard-coded'.

Joe


Attachments:
page13.jpg
page13.jpg [ 55.44 KiB | Viewed 970 times ]
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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Fri 22, 2017 1:31 am 
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Joined: Dec Thu 14, 2017 5:08 pm
Posts: 5
Location: Toronto, ON
Joe,

How did you manage to come across the information that you provided in the attachment. No where in the service manual does it document the AM frequency band range based on the country.

You must have connections ... :)

Regards and thanks,
Gus


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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Dec Sat 23, 2017 5:31 am 
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Joined: Dec Wed 16, 2015 10:31 pm
Posts: 203
Location: Toronto ON
Gus,

That chart is from the data sheet for the IC that controls the tuner. I downloaded the schematic and noticed it had the TC9173 controller IC, so in trying to determine if it could be programmed for extended coverage I found the data sheet and extracted that info.
I got connections alright...

Merry Christmas!!

Joe


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 Post subject: Re: NAD 7240PE AM freq range
PostPosted: Jan Sat 27, 2018 6:16 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1421
Location: Cambridge MN USA
The Q of those early varactors was particularly poor on those expanded band frequencies. Got a Panasonic made radio from a 91 Nissan Pathfinder and strong, nearby stations just below 1600 would easily bleed over stations above 1600.

Scott Todd


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