----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
To: <tentec@contesting.com>
Sent: Monday, September 21, 2009 5:05 PM
Subject: Re: [TenTec] Orion drops lock?
> 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.
>>
Yea...my Dad used to see the tightened screws in the cans during WW2 in the
signal corp.
Later, when I was about 8, he taught me the rudiments of aligning simple AM
broadcast radios.
These were simple 5 tube radios with the tube filiments in series, and no
transformers. So I also
learned not to reverse the plug in the wall and get zapped. Later, when I
knew enough, I changed those plugs
to 3 prong of course.
LOL...it was fun and I lived.
73
>> 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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