On Mon, 2009-09-21 at 13:16 -0400, Martin Ewing wrote:
> 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.
That's true, but by applying the heat and cold technique you can isolate
the most temperature sensitive capacitor or coil and that's most likely
in a VCO that needs a change in alignment. Turning the screw the wrong
way makes it worse, the right way solves the problem.
And if there is more than one phase locked loop, you can't tell from the
out of lock indicator which one it is. It could be one, it could be all
from loss of reference signal.
>
> 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.
I knew better because my dad had a radio service shop in a corner of the
living room when I was very little, but I did learn to align radios at
an early age to correct those who did tighten all the loose screws.
Tightening loose screws is not a bad restoration technique if they are
providing grounds, like shields and PC board mountings. I've fixed many
a radio by suggesting the board mounting screws be tightened. Including
several of my own. And that also applies to Collins S-line tube sockets
which were often used for circuit grounds.
>
> In these digital days, it seems strange if circuits are drifting like this.
There are still analog circuits in the VCO that the digital stuff locks
to frequency.
> 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.
And while I'm not the only one that thinks its a VCO problem going out
of lock, ALL ICs that heat can break internal connections when the
plastic expands faster than the bond wires, and the heat/cold technique
can identify those parts.
>
> 73 Martin AA6E
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