[time-nuts] Wenzel Oscillator Repair
Joseph M Gwinn
gwinn at raytheon.com
Wed Jan 21 11:06:31 EST 2009
time-nuts-bounces at febo.com wrote on 01/20/2009 04:47:26 PM:
> Joseph M Gwinn skrev:
> > time-nuts-bounces at febo.com wrote on 01/20/2009 04:32:15 PM:
> >> Bruce Griffiths skrev:
> >>> The relatively low thermal conductivity of the steel can will help
> >>> considerably in avoiding thermal damage if the heat is
> >> applied to the joint.
> >>> If the can were copper it would be much more difficult to avoid
> > thermal
> >>> damage.
> >> When I needed to have a McCoy oscillator can opened my
> trusty good old
> >> friend Sten did the usual trick of pre-heating the can and then when
> >> applying heat to the solder the thermal difference is lower and hence
> > the
> >> heat-flow away from the joint. Didn't take much time and I think the
> >> oscillator is 100% intact.
> >> Pre-heating and hot air are his main tools for tricky
> soldering jobs. He
> >> has low fatality rate on problems like that. This is why we
> let him do
> >> that kind of stuff at work.
> > I imagine that Sten works *very* fast. I've found that when soldering
> > thermally sensitive things like small coil bobbins made of
> nylon that a
> > high temperature and relatively large iron is best - the
> terminals come up
> > to temperature almost instantly, and it's all over before theheat can
> > spread and melt the bobbin.
> > Hot air has the advantage over a flame that overtemperature
> is less likely
> > with hot air.
> Actually, the pre-heating takes a bit of time... but then it doesn't
> take much effort to push the solder over to melting and it took
> relatively little time. The pre-heating doesn't go all the way up there,
> so melting of plastics isn't really a problem.
> The pre-heating trick actually makes the big soldering iron rest most of
> the time...
> We have boards with so much ground/power grids that it is really a
> headache to do without pre-heating, which is similar to the iron case
> soldering problem.
> So, doing it this way makes it go fast.
I think we are talking about different things. For getting chips off a
big multilayer board, preheat plus hot air is a standard way to go, but we
are talking about how to unsolder a steel can with foam insulation within.
Slow heating to near soldering temperature is likely to yield a heap of
The point of the torch method is to heat the can's solder seam up *fast*,
so the solder melts before the foam.
More information about the time-nuts