[Boatanchors] Relay Repair - Demagnetization Question

[J. Forster]

Dennis,

You're right on the distinction.

It certainly does work on stored unit failures. The high voltage punches
through the non-conducting layer and the overdrive burnishes the contacts
more than in normal operation.

I prefer the DC approach, because you can hear the thing start up and for
safety's sake. A current limiter is absolutely required, IMO, and a light
bulb works well.

Once a unit starts up, I run it for a minute or two to thouroughly clean
the contact areas.

-John

=================

> 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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