Most common faulty part in old electronic gear

[olds...@tubes.com]

Regarding this kind of switch:

http://www.parts-express.com/data/default/images/catalog/240/060-908_HR_0.jpg

When it comes to working on old electronic gear from the 1950s thru 70s
or 80s I keep reading the most common fault are the old paper/wax
capacitors and electrolytics.

While there is truth to this in some cases, I have found a part that
fails about 90% of the time on these old devices. They are these old
slide switches (shown above). I just picked up an old Sencor Substitutor
box from the 50s or 60s. The caps and resistors are not looking to be
bad, but all three of the slide switches are junk. Even after sliding
them back and forth 100 or more times, they are erratic at best, or dont
work at all. (I am awaiting a can of Deoxit from an online order, since
I can not buy it locally). I have my doubts that even this stuff will
fix these switches.

Do they make more reliable replacements for this type of switch that
will fit the same holes? Heck, even in the 70's when they were only a
few years old, these switches were troublesome.

I never understood the reason for gold plated speaker terminals, but
these switches should be gold plated, or something done to them, since
they were always faulty.

[Jeff Liebermann]

On Thu, 09 Mar 2017 01:58:01 -0600, olds...@tubes.com wrote:

>Regarding this kind of switch:
>http://www.parts-express.com/data/default/images/catalog/240/060-908_HR_0.jpg

>I have found a part that
>fails about 90% of the time on these old devices. They are these old
>slide switches (shown above).

See the 4 little tabs holding the switch together? Bend them straight
and the slide switch will come apart. Be sure to catch the contacts,
springs, and balls before they disappear into the carpet. Clean out
all the gunk and goo that accumulates in such switches. If the
contacts are pitted or damaged, get a new switch. Reassemble.

However, there's some debate as to how to lube these switches and with
what manner of lube. I used to use contact cleaner (mostly solvents
and some residual oil) but found that the slide switches didn't last
more than a year or two before they again needed "cleaning". So, I
switched to using grease, which was probably the original lube. I
should use dielectric grease, but found that almost anything will
work.

>I just picked up an old Sencor Substitutor
>box from the 50s or 60s. The caps and resistors are not looking to be
>bad, but all three of the slide switches are junk. Even after sliding
>them back and forth 100 or more times, they are erratic at best, or dont
>work at all. (I am awaiting a can of Deoxit from an online order, since
>I can not buy it locally). I have my doubts that even this stuff will
>fix these switches.

What you might find when you disassemble the switches is a tar like
goo covering the contacts. This is a mixture of the original lube,
dust, dirt, filth, corrosion, and possibly the remains of the last
attack by contact cleaner. The worst I've seen is drywall dust. The
switch contacts ride on top of the tar and don't make a connection.
There are also contacts that have holes blown into them by arcing or
moving the switch with current going through the switch. I would not
expect that on a substitution box.

Incidentally, I have fair collection of RF attenuator boxes that use
slide switches. something like this:
<https://wb6amt.com/96db-attenuator-kit/>
The switches need to be very clean for the device to perform properly.
The difficult part is determining which switch is failing because all
the switches are in series. I will confess to using contact cleaner
on these because taking disassembling the switches is rather
difficult.

>Do they make more reliable replacements for this type of switch that
>will fit the same holes? Heck, even in the 70's when they were only a
>few years old, these switches were troublesome.

Sure. Reputable manufactory, correct contact material, and some kind
of seal will help. Start here:
<http://www.ckswitches.com/product-selection/slide/>

>I never understood the reason for gold plated speaker terminals, but
>these switches should be gold plated, or something done to them, since
>they were always faulty.

Gold plating should be used for dry loads (i.e. no DC component). If
you want DC, use silver. For and RF attenuator or a capacitor
substitution box, I would use gold. For a resistor or inductor box,
silver.
<http://www.digikey.com/Site/Global/Layouts/DownloadPdf.ashx?pdfUrl=A80C3BB324E14E7E80F19776A15429E4>
There are also gold and silver alloys to improve things:
<http://www.contactechnologies.com/Contact-Technologies-Materials.htm>


--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Boris Mohar]

On Thu, 09 Mar 2017 01:58:01 -0600, olds...@tubes.com wrote:

>Regarding this kind of switch:
>
>http://www.parts-express.com/data/default/images/catalog/240/060-908_HR_0.jpg
>

http://www.ckswitches.com/product-selection/slide/


Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place



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[Jon Elson]

olds...@tubes.com wrote:


> While there is truth to this in some cases, I have found a part that
> fails about 90% of the time on these old devices. They are these old
> slide switches

Oh, yes! Those old stamped metal slide switches with the phenolic wafer
with the contacts in it were quite awful, and had a short life before they
started getting flaky contacts. It might be partly the open nature of the
switch, lets lots of air get to the contacts. I just repaced some pretty
decent PCB mounted push-push switches that were a definite cut above the
cheap ones, but still had a sliding contact spring. But, air and maybe loss
of lube had caused the contacts to deteriorate. Exercising the switches
just made them worse. This was on 36-year old scientific equipment.

Jon

[pf...@aol.com]

A lot of this has to do with location and storage. I have a lot of Dynaco audio stuff - and David Hafler was notorious for using low-bid/surplus/salvage and "seconds" stuff - that are generally pretty much fine as they have never seen damp, a garage, or unconditioned space in their 38 - 57 year histories. I have a number of vintage radios (TransOceanics) that are up to 30 years older that are also pretty good - as Zenith went at least one step up in initial quality. These switches get flushed before first use in any case.

But rotary and pot switches are a different story. Those I have had to learn to restore and/or rebuild. A PITA, but there are usually only a few bits inside to go bad.

As to caps - unless they are potted or PIO caps, I do not even bother - they get replaced out-of-hand. It is not a matter of "if" but "when".

Enjoy!

Peter Wieck
Melrose Park, PA

[pf...@aol.com]

And:

There are kits out there for restorers:

http://www.wisconsinpartsdatabase.com/WISCONSIN/Machine-Parts/Replace/New/Qty-rs-radiospares-maka-switch-rotary-wafer-switch-kits.pl