On Mon, Sep 21, 2009 at 12:16 PM, Dr. Gerald N. Johnson <geraldj@weather.net
> wrote:
> On Sun, 2009-09-20 at 14:39 -0400, Martin Ewing wrote:
> > Right, but is there a do it yourself prescription, short of digging in
> with
> > the probes and actually trying to *understand* things? (Awful thought!)
> I
> > could/will ask TT, but I wonder if anyone has done it out there. (Shame
> > that there is no repair manual.)
> >
> > I can't make the condition appear on command, so that complicates
> matters.
> > It's intermittent. Experience (more than I have with the Orion) would
> > probably help...
>
> Often an intermittent can be forced by applying alternate heating and
> cooling. A hair dryer or hot air gun supplies heat and a spray can
> product like Freeze-Mist or even the dry air lens cleaners provide cold
> from the rapid expansion of a compressed gas. Start with a large area,
> and if that triggers the problem, then cut the area in half, until the
> part is located. That's called a binary chop when writing a computer
> program for searching. Half the area previously searched.
>
> Then maybe you will find (the circuits are available) that you have hit
> on a temperature sensitive capacitor part of a VCO and all you need to
> do is to turn the slug in a coil ten degrees in or out to get it back in
> range. With the controlled failure induced by heating and cooling, you
> can soon find which way is an improvement. It is possible to overheat
> circuit boards with some hot air guns, like those made for paint
> removal. You don't want that much heat. The $12 hair dryer can be
> enough.
> >
> > 73 Martin AA6E
> >
> 73, Jerry, K0CQ
>
Thanks, Jerry, all good suggestions.
There can't be that many PLL's in the synthesizer chain, so finding the
circuit probably is not a big problem. The reason I'd hesitate to do trial
and error is that you could just as easily make things worse as fix them
without having some guidance on which screw to turn and which test point to
watch.
I am reminded of the would-be jr. tech who thought he'd help out his dad by
tightening down all the screws in those funny IF transformer cans. I name no
names.
In these digital days, it seems strange if circuits are drifting like this.
I wouldn't be the first to note that some of the Orion boards run rather
hot, and a cooling fan might have helped prevent some of these issues.
73 Martin AA6E
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