[Premium-Rx] WJ-8615D Issues.

Wed Aug 7 16:53:35 EDT 2013

David,

Is it the original fan?
B1 Blower Fan 1 180507-1 14632 Comair Rotron

Is the fan filter installed?
TYPE 796638-1 FAN FILTER ASSEMBLY

Best Regards,
Steve

----- Original Message ----- 
From: "David Schofield" <davesc50 at tiscali.co.uk>
To: <Premium-Rx at mailman.qth.net>
Sent: Wednesday, August 07, 2013 1:40 PM
Subject: Re: [Premium-Rx] WJ-8615D Issues.

> Hi Again,
>
> For anyone interested in the "solution" to the SSB hum issue, I discovered 
> the following;
>
> The hum was due to ac ripple being superimposed on the 10.7Mhz reference 
> signal to the SSB converter.
> It looks like my replacement PSU isn't quite as smooth as the original one 
> used by WJ.
> An extra 4700uF across the +15v rail removed about 85% of the problem, the 
> remaining hum however has kept me guessing....
> The only "cure" I have found so far is to disconnect the fan.
> Somehow the noise on the supply rail is being induced by the fan, in fact 
> if I physically slow the fan down, the pitch of the hum changes....
> I have tried all sorts of things to filter it out, but can not remove it 
> 100%
> As the noise is only very faint now, and was only ever audible on SSB, I 
> have come up with a compromise solution.
> I am hardly ever going to use this Rx on HF, or SSB, so have utilised an 
> existing unused hole on the rear of the unit designed for the ac mians 
> voltage selector switch, (unused as both the original switch mode PSU 
> fitted by WJ, and my supply are both dual voltage), and installed a fan on 
> / off switch.
> This means that I can switch off the cooling fan if I want to listen to 
> crystal clear SSB, and leave it running for the remainder of the time.
> Whilst this is not an ideal solution, it works OK for me, is fully 
> reversible, and I don't see it causing any major cooling problems, as the 
> Rx is not rack mounted and has large rubber feet fitted to the base 
> allowing for plenty of air flow.
> The PSU I used is also nearly double the rating of the original one and 
> runs a lot cooler.
>
> I'm still open to suggestions, if anyone out there knows how to prevent 
> induced noise from a fan getying back into a power supply. I have tried 
> ferrite beads, filter caps Etc, but can't clear it up.
> I suspect that the problem still lies with my replacement power supply as 
> opposed to the receiver design, but as I never had it working with the 
> original supply, cant prove or disprove this.
>
> Anyway, it works fine now.
> Thanks to everyone who replied to the original mail with lots of usefull 
> info as well.
>
> Cheers,
> Dave. S.David Schofield <davesc50 at tiscali.co.uk> wrote:Hi All,
>
> I've just acquired a WJ-8615D which to the most part is working very well 
> indeed.
> When it first arrived the PSU had failed spectacularly, and after a couple 
> of atempts at rebuilding it I decided it was beyond salvation....
> To that end I brought a more up to date, better spec'd PSU and made up a 
> set of adaptor leads, and a plate to fit the new module so an original 
> unit could be fitted should I ever find one, or actually succesfully fix 
> the original.
>
> The receiver is now functioning well, apart from the fact that the SSB 
> demodulator has a loud hum of approx 50Hz superimposed on the output.
> Before I start to investigate this, I was wondering if their are any known 
> issues that can cause this. I suspect a bad earth, or possibly a failed 
> decoupling capacitor on the SSB module. The new PSU seems to be performing 
> 100% ok, so I think this is a secondary fault.
> SSB seems to be working OK underneath the hum, so it would be nice to get 
> it working 100% ok.
>
> The other thing is that this unit is fitted with the optional oreselector, 
> which appears to be making it pretty deaf, although it does seem to be 
> doing it"s job and improving intermodulation Etc. especially on HF.
> If I bypass the preselector the gain is far better, but full of harmonics 
> Etc, is this normal for these receivers?
> If it is I can live with it, I have plenty of other "hotter" receivers, 
> and would rather have reduced gain than spurious images, but though I'd 
> ask in case their are any known issues in this area either.
>
> Thanks in advance,
> Dave. S.
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