Hi Gary,
Thanks! I'll check the switching diodes first as the easiest thing to
remedy before engaging your kind offer of trying a spare board. The
temporary 0.01 uF capacitor across the bandpass filter reminds me of a
similar technique I used to diagnose a bad switching diode set in an old
Kenwood TS-820. Worked great; highly recommended as a diagnostic tool to
anyone reading this email later on who has a similar problem.
73
Phil W1PJE
On Sun, Dec 30, 2018 at 2:46 PM MadScientist <dukeshifi@comcast.net> wrote:
> More likely than alignment as an issue, would be the switching diodes for
> 12 meters, or, again, bad soldering of the circuitry around those diodes
> and associated coils.
>
> You can check the continuity of the tuned coils in-circuit since the
> shunting paths are say to account for.
>
> Also, try connecting a 0.01 uF capacitor across the entire bandpass filter
> (Cathode of D21 to Cathode of D22 will accomplish this) and see if receive
> level reaches near-expectation level. This will prove that you are looking
> in the right place.
>
> Do not transmit under this condition1
>
> Gary
>
> > On Dec 29, 2018, at 2:40 PM, Phil Erickson <phil.erickson@gmail.com>
> wrote:
> >
> > Hi all,
> >
> > More investigation has narrowed the problem to the BPF/front end board
> > 81593. We'll use 15 and 10 meters as our "working normally" and 12
> meters
> > as "working abnormally" for this discussion:
> >
> > - LO input from the XO-LO board at connector 26 is at exactly the right
> > appropriate frequency for a 9 MHz IF, and nearly constant voltage for
> > 15/12/10 meters. That eliminates the XO-LO board as the problem
> (relief!).
> > - TX input at connector 27 is also nearly identical on 15/12/10 meters.
> > - However, the output at connector 24, which goes off to the low level
> > driver board, is not the same for all three.
> >
> > Using a 1 Mohm input impedance on a Tek 2465A scope:
> >
> > 15, 10 meters: in TUNE mode, signal increases with PWR knob up to
> > about +/- 2V at three dots up from minimum (10:30 am clock position) and
> > then essentially saturates
> > 12 meters: in TUNE mode, signal increases with PWR knob but only up to
> > about +/- 0.12V at three dots up from minimum and then essentially
> saturates
> >
> > Not sure why the signal is saturating at the 10:30 am position as I
> would
> > have figured it would go up as I turned PWR up further. (It does go up
> to
> > a clean 90 watts or so on 15 and 12 meters when everything is hooked back
> > together.) No matter; the problem is clearly in low output at 12 meters
> > from 81593.
> >
> > Since 81593 has individual BPFs for each band that are used for both TX
> > and RX, my guess is that the BPF is off frequency for 12 meters which
> would
> > explain why I have a relatively deaf receiver by 20 dB on that band as
> well
> > as low TX output.
> >
> > Now the next question to this group: does anyone have the alignment
> > procedure for a 81593 BPF/front end board? The manual does not describe
> > one. I am also very careful about adjusting slugs as like many of you,
> > I've had inductor cores snap in two with too much pressure, so I want to
> do
> > the minimal amount of tweaking to fix the problem and not do too much
> > "golden screwdriver" wiggling back and forth. Knowing what to inject and
> > where to inject it would be great. (I have HP signal generators and the
> > like available.)
> >
> > This list is really terrific - and thanks to Gary W0DVN and Pete in
> > particular!
> >
> > 73
> > Phil W1PJE
> > _______________________________________________
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>
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--
----
Phil Erickson
phil.erickson@gmail.com
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