[Boatanchors] Relay Repair - Demagnetization Question

[mac]

A distinction has to be drawn here between vibrators  that fail in  
service and vibrators, military or otherwise, that fail to operate  
following long periods of non-use.  The latter problem as Robert  
points out is due to a chemical buildup on the contacts.  I am certain  
this is not limited to military units and is the type of problem most  
commonly encountered today.  This buildup is very hard and some  
significant mechanical burnishing effort is required to remove it.  I  
have never tried the 115vac/series lightbulb treatment that several  
claim to have used with positive results.  I 'm skeptical (given how  
hard the gunk is to scrape off mechanically) but plan to give it a  
shot one day.

Dennis D. W7QHO
Glendale, CA



On Feb 2, 2010, at 5:37 PM, Carl wrote:

> I wouldnt know about military vibrators as Ive no interest in them.  
> Nor do I know if they are constructed any different than civilian  
> versions.
>
> Automotive type whether used by hams, public safety, or whatever  
> often have the contacts stuck together and 6 or 12VDC often wont  
> budge them loose. Trying it too long is guaranteed to damage the  
> contacts.
>
> It only takes a little AC, no string of lamps or 120VAC involved; a  
> 6 or 12VAC filament transformer works fine. Ive been doing this  
> since the 60's when I started rebuilding vintage auto radios for  
> owners. Many hundreds also including the 38 Buick I finished 2 days  
> ago.
>
>
> Carl
> KM1H
>
>
>  ----- Original Message -----
>  From: WA5CAB at cs.com
>  To: km1h at jeremy.mv.com ; boatanchors at mailman.qth.net
>  Sent: Tuesday, February 02, 2010 5:04 PM
>  Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question
>
>
>  No.  At least not the military ones.  The problem with them, after  
> decades of inactivity, is that the contacts are covered with a non- 
> conducting layer of tungsten sulfide (or maybe supphate, I never  
> looked up the relavent valences) caused by sulfur outgassing from  
> the sponge rubber sleeve inside all the cans.  I've "fixed" hundreds  
> of them.  You can open up the can and burnish the contacts but it's  
> a lot less trouble to use an array of 120 volt 12 to 40 watt lamps  
> and the 120 VAC line to do the job.
>
>  This works on all of the military vibrators except for the VB-5,  
> which can only be fixed by opening the can.  Which always comes open  
> in little pieces of brittle aluminum and has to be replaced.
>
>  In a message dated 2/2/2010 2:21:57 PM Central Standard Time, km1h at jeremy.mv.com 
>  writes:
>
>    Automotive and other vibrators do not have coil problems. The  
> contacts are
>    "welded" together from basic chemical reaction after decades of  
> storage.
>    Applying 6-12VAC across the proper actuator contacts will get it  
> swinging
>    again.
>
>    Carl
>    KM1H
>
>
>
>  Robert & Susan Downs - Houston
>  wa5cab dot com (Web Store)
>  MVPA 9480
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