[Premium-Rx] WJ-8716 intermittent problem

[Mark Donaldson]

Tim,

My first guess would be a VCO in one of the
synthesizers is losing lock, take a look on the
synthesizer boards and see if the loop unlock LED is
indicating an unlocked condition when this is
happening. The synthesizers in the 8716 are not hard
to troubleshoot as long as you have a manual with
schematics, synthesizer replacement parts are still
available.

Mark Donaldson WA1QHQ

--- Tim Shoppa <shoppa at trailing-edge.com> wrote:

> After sitting on the shelf for a few months, I fired
> my WJ-8716
> back up again.
> 
> It worked fine for about 20 minutes, and then went
> into this weird
> situation where the symptom was: on all filters
> except for 16kHz,
> it sounded like a regenerative receiver with the
> gain set slightly
> too high. As signals went up and down it sounded
> like it was
> breaking out in self-oscillation. This happened in
> all modes
> and all bandwidths EXCEPT 16kHz.
> 
> But there was also this weird interaction with main
> tuning: it
> was most likely to obviously exhibit this symptom
> when tuned just below
> X.XX5 MHz. e.g. it would do it if I was listening to
> 5.924999 MHz
> but then largely (but not completely) go away if I
> went to 5.925 MHz.
> 
> After leaving it on a few days, this all went away.
> 
> Is this a known problem? If I look at the
> schematics, then the
> self-oscillation except on 16kHz bandwidth
> looks like it might have something to do with the
> IF strip. I see all these switching transistors to
> allow digital
> switching between the different IF bandwidths and I
> suppose it's
> possible that one of those might be leaky in a way
> allowing
> regeneration possibly through coupling in the
> digital control lines.
> 
> But then there's that weird interaction with main
> tuning,
> which takes me into the world of the synthesizer, a
> place I'd
> rather not go.
> 
> I suppose it's possible that it's the IF strip
> interacting with
> the synthesizer in some weird way, either feeding
> back into the
> synth's local oscillator outputs, or maybe even
> coupling in the
> power supply despite all those bypass caps.
> 
> Any advice or collective wisdom? Maybe I'll just be
> sure to use
> it a couple hours a day from now on, and not let it
> sit on the
> shelf!
> 
> Tim.
> 
> 
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