[Boatanchors] Relay Repair - Demagnetization Question

[J. Forster]

Almost all the vibrators I've see have a different problem.

The contacts are coated with some kind of non-conductive film. These can
often be repaired by hooking them up as a buzzer to a higher than normal
voltage supply, through a load like a 100 W incandescent light bulb, then
giving the case a rap with screwdriver handle to get it atarted.

I think the film might be caused by the catalytic effect of the platinum
series metal in the contacts aiding a reaction of the organic vapors
outgassed from other internal parts.

-John

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


> 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
>
>
> ----- Original Message -----
> From: <WA5CAB at cs.com>
> To: <boatanchors at mailman.qth.net>
> Sent: Tuesday, February 02, 2010 2:23 PM
> Subject: Re: [Boatanchors] Relay Repair - Demagnetization Question
>
>
>> Although not technically hermetically sealed, plug-in vibrators (except
>> VB-16) are sealed well enough to have this problem.  According to my
>> experience, the MTBF of NOS units was 40-50 years.  I first noticed it
>> occurring with
>> WW-II vintage units in the late 80's.  By the mid 90's it was showing up
>> in
>> Korean War vintage units.  Today I assume any unused vibrator will not
>> work
>> initially out of the box.
>>
>> It has nothing to do, of course, with magnetics.
>>
>> In a message dated 2/2/2010 12:10:13 PM Central Standard Time,
>> jhhaynes at earthlink.net writes:
>>> When the use of hermetically-sealed relays first started, especially
>>> in the military, there was a surprising development of contact
>>> failures.
>>> After all, you'd think that a sealed relay couldn't get dirty contacts.
>>> It turned out that organic substances outgassing from the winding
>>> would, with the help of a little sparking, form an insulating goo on
>>> the relay contacts.  So for a while there was a doctrine that you
>>> don't use a sealed relay unless the situation absolutely requires it;
>>> that a simple dust cover is much better for contact reliability.
>>>
>>> There is an awful lot of lore about contacts and their problems and
>>> solutions.
>>>
>>
>> Robert Downs - Houston
>> wa5cab dot com (Web Store)
>> MVPA 9480
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