[Premium-Rx] WJ URR-74 (WJ-8718A) issue

[fintronics .]

Hi Karl and thanks very much for the reply and extremely useful information.
Unfortunately all my test gear is boxed in storage awaiting the completion
of my new hamshack/listening post/workshop. Fortunately I was able to find
a service manual online (BAMA?). I'm going to start with the simple for
now, checking the coax interconnects, card edge connections, etc.... I may
pull out the LO synth card and have a look.... I know on some of these
receivers, aging tantalum caps can cause problems...


On Sat, Feb 11, 2017 at 1:10 PM, sm0aom at telia.com <sm0aom at telia.com> wrote:

> Your two questions:
> The Nicad battery is for keeping the last settings of the front panel,
>
> Without it,the frequency will be a random setting whenever the receiver is
> turned on.
> It may be time-consuming to enter the frequency again as there is no
> keypad.
>
> The 20 kHz spurious response is a consequence of the frequency generation
> and mixing schemes in the receiver.
>
> There are two synthesisers in the receiver; one that provides the LO
> signal for the first mixer in 10 kHz steps generated by dividing a 40 kHz
> step signal by 4,
> and another for the second mixer that interpolates between the 10 kHz
> steps in 10 or 1 Hz steps.
>
> These synthesisers have a finite reference sideband suppression, so there
> are responses at every 10 kHz around the center frequency. In your case,it
> appears that a 20 kHz separated sideband is strong enough to create a
> response.
> The reason that the response disappears when the frequency is changed by
> 10 Hz is that at the limits of the second LO synthesiser tuning range, when
> the 10 kHz figure is changed the frequency of the first LO is changed by 10
> kHz, and the conditions for receiving the spurious responses are not
> fulfilled any longer.
>
> These forms of responses may point to an alignment or component ageing
> condition in the first LO synthesiser, when the reference sideband
> suppression has detoriated.
>
> It may also be a signal leakage condition between the first and second IF
> parts of the receiver.
>
> The proper way of investigating these kinds of problems is with a very
> clean signal generator and a spectrum analyser.
>
> 73/
> Karl-Arne
> SM0AOM
>
> ----Ursprungligt meddelande----
> Från : fintronicsusa at gmail.com
> Datum : 2017-02-11 - 17:17 (UTC)
> Till : premium-rx at mailman.qth.net
> Ämne : [Premium-Rx] WJ URR-74 (WJ-8718A) issue
>
> Reveived my  URR-74 last night.. what a beautiful receiver!. Just about
> mint condition, incredible internal construction... While inspecting the
> inside, I noticed one of those nicad battery modules soldered on to one of
> the plug-in PCB's. The 4 pins were green with corrosion as were the pads on
> the solder side of the board. Quite the pain in the butt to remove and I
> spent quite a bit of time cleaning up the mess on both sides of the board
> but now the battery module is removed and the board is cleaned up with no
> open or corroded traces.
>
> Since this receiver has no microprocessor, I'm wondering what the heck a
> battery backup/module would be used for? There are no memories, etc...
> Figured I'd power it up without a battery and see what happens.
>
> So on to powering it up....It didn't come with a power cord so I powered it
> up with a line cord/alligator clips to that 3 pin rear panel connector.
> Headphones, outside wire antenna... fired it up... It's working! ....
> Switches and pots are very dirty but I'm hearing signals, all modes, all
> filter positions working... but then.....
>
> I noticed the strangest thing while tuning across some SW and AM BCB
> signals. While tuned to an AM BCB station on 840khz, I noticed what appears
> to be an image of that signal exactly 20khz down from 840khz.... and here's
> where it gets strange... While tuned to the image signal at exactly 820khz,
> if the tuning is moved even 10hz above 820khz the image signal disappears!
> completely!.... but if tuned at or below the image at 820khz, the signal is
> there, as if only receiving one sideband of the AM signal... This happens
> on all AM signals regardless of band or frequency....
>
> What the heck?... could this be related to the missing battery? (doubtful),
> .... I did notice when I had the receiver open that some of the SMA coax
> interconnect cables were loose... ... maybe this is a problem with
> frequency data to the synth getting corrupted?.... don't know...
>
> Any ideas? where to start looking?.
>
> Thanks...
>
> Glenn
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