[DSP-10] U7 not locking up

[Luis Cupido]

Hi Doug,

This problem has been hapening to too many people now,
Your description is quite correct and also acording my observations.
My solution was using the only available inverter on the board
but for that I had to change the DSP code (to invert the signal)
If someone want to avoid  the dead-bug construction I can send the
DSP code.
Otherwise the 2 inverter solution is indeed the way to go.

I would bet this is the only problem Larry has.

Luis Cupido.
CT1DMK.


----- Original Message -----
From: "Doug Bade" <dbade@clecom.com>
To: <dsp-10@mailman.qth.net>
Sent: Friday, August 01, 2003 2:58 PM
Subject: Re: [DSP-10] U7 not locking up


>          I had a problem with bad loading and another user suggested (as
he
> had found) that the wave forms from the dsp were being severely rounded
off
> coming into the latch/registers. I too found this. His suggestion was to
> wire around the bypass caps temporarily and see if it got better... it
did.
> ( they are a large part of the problem) He then suggested using a buffer
to
> buffer the clock line (as I recall) and clean it up and more especially
> square the wave form up.. I speculate the sloping curvature of the leading
> edge was causing the latch/registers to lock up inconsistently and without
> proper data being ready ( because of variations in trigger thresholds)...
> It fixed my problem, and it has been fantastic on loading since then. I
> used a dead bug mounted chip on the radio side of the feedthru caps, and
> inverted twice and all was well..
>          In theory, as long as the data was ready first, it should not be
> an issue, but I beleive internal scrambling of the data was occurring
> because rise time was exceeded (inside the register chips) , and/or noise
> on the signal at threshold... again I am speculating, but I did observe it
> and it did correct it with the fix....
>
>          A scope showed a very curved leading edge on the clock signal
> coming through the feed thru's..
>
>          This may have nothing to do with your problem, but it indicates
to
> me the pulse quality is borderline after filtering through (at least some)
> feedthru's and might be one of those too close situations where tolerances
> push one way or the other....go or no go...
>
> Hope it helps some anyhow...
>
> Doug KB8GVQ
>
>
> At 06:56 PM 7/31/2003 -0700, you wrote:
> >Hi Mike,
> >
> >I rechecked all the corrections thru rev 4.5 and everything looks OK. The
> >voltage on U6-3 is 2.47V. I built my unit from a TAPR kit, no parts
> >substitutions. When I load the PLL diagnostic program I see data moving
on
> >U7-5&7 and pin 6 goes low for awhile. It appears that the wrong data is
> >being loaded. I just got another email from Chuck, WA6EXV, and he is
still
> >having the same problem. He tried changing the MC145170 but that did not
> >help. Any more ideas?
> >Thanks for the quick response.
> >73's Larry  K6HLH
>
>
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