Hi Ken,
Thanks for your quick reply. The filter is shared and switched by either of
the 15M or 12M enable DC voltages. The 15M and 12M switching voltages are
"ORed" by diodes D33 and D34 near connector 86. As such, a bad contact to
either of the diodes would not make both bands fail. Therefore I believe that
it's something in the filter itself.
I will first reflow the solder to the BA482 switching diodes, D38 and D43, to
the filter, in the hope that the problem may be a cracked solder joint whose
resistance is sensitive to thermal expansion. However, because of the
repeatability of the fail going away after a short warm up, I'm beginning to
think that either BA482 might be marginal; the series on-resistance drops with
increasing temperature and may be too high at room ambient but ok to pass the
L.O. signal at elevated temperature.
Once I remove all the cables to the back of the rig and take it down from the
shelf I'll scope the L.O. signal to see how it compares with other bands. I
should still be able to see the L.O. signal in RX mode (but not in TX mode)
even with the LL driver/NB and FM boards removed. Then I'll check the
distribution of the switching voltages while pressing gently on components of
the filter.
I plan on calling TenTec this coming week to see what they think about this
problem, and order some BA482's at the same time.
73,
Jack K1VT
-------------- Original message from Ken Brown <ken.d.brown@hawaiiantel.net>:
--------------
> Hi Jack,
>
> I think in you post the method you intended to use will work out fine.
> That is taking plenty of pictures along the way. I did not take any
> pictures, and wish that I did take a few. Got though it okay though. No
> particular tricks to getting it out. Make sure the numbered labels are
> intact on the cables or connectors that plug into the board.
>
> I wonder if the bandpass filter is not working reliably because of
> something easier to fix, such as dirty contacts on the connectors that
> route the band select information from the logic board to the XTAL
> OSC/LO Mixer board? You might try checking the voltages on those lines
> to see if they are up to par when in the bands that are giving you
> trouble, or just clean and exercise all the connectors.
>
> Ken N6KB
>
>
> modeler@bellsouth.net wrote:
> > Ken,
> >
> > Do you have any tips for accessing and removing the XTAL OSC/LO Mixer
> > board? I need to reflow solder connections associated with the 15/12M
> > filter, or possibly replace BA482 diodes. Please see my recent post.
> >
> > Thanks.
> >
> > Jack K1VT
>
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