[time-nuts] Wenzel Oscillator Repair

Joseph M Gwinn gwinn at raytheon.com
Wed Jan 21 11:06:31 EST 2009


Magnus,


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 
goo. 

The point of the torch method is to heat the can's solder seam up *fast*, 
so the solder melts before the foam.

Joe




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