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From: James Sweet on 2 Feb 2010 02:18
Wild_Bill wrote:
> The method I use for cleaning those conductive pads on button switches
> (keyboards, IR remote controls, etc) is very lightly scuffing them with
> a pen-type tool that has strands of glass fibers in it.
>
> It can be difficult to determine the "normal" resistance of these types
> of contacts, because typically, the resistance decreases as more
> pressure is applied to the button.
>
> The button pads that are shiney, somewhat glossy, are the ones that need
> scuffing, IME.
> I lightly scuff the conducive pads just enough to remove the shine,
> sometimes just a few passes across the pads.
>
> I can never be certain how long the scuffing treatment will last. Most
> times the problem is corrected for at least a couple of months to about
> a year, maybe longer.
>
> The tool I use was found in a camera department of a retail store years
> ago, as a battery contact cleaning tool. I've read numerous comments
> that the same type of tool is available at autobody shop supply places,
> as a scuffing tool for small chips in in painted surfaces on car bodies.
>
> I would also like to know if any conductive paint-type products work
> effectively, and are somewhat permanent.
>
> --
> Cheers,
> WB
> .............
>
> "DaveC" <invalid(a)invalid.net> wrote in message
> news:0001HW.C78BD8D601BE4002B08A39AF(a)news.eternal-september.org...
>> A little more info on my non-functioning button problem:
>>
>> I disassembled the front of the scope -- bezel, buttons, front panel
>> assembly.
>>
>> The elastomer button strip (the "rubber' buttons) have a conductive
>> backing
>> which presses down onto the menu flex circuit (flex pcb).
>>
>> The back of the button looks good (very light wear indications). The flex
>> circuit traces are not metal, which surprises me. It's made from pretty
>> fragile carbon-like traces.
>>
>> When I measure the continuity of the closed contacts of a button that
>> works,
>> I see approximately 200 ohms. Closed contacts of a button that doesn't
>> work,
>> I see 400 ohms (sometimes more).
>>
>> What resistance should I see at the contacts when the button is pressed?
>>
>> Can I clean these contacts with alcohol? Or...?
>>
>> Can the traces on the flex circuit be renewed (ie, silver-bearing paint)?
>>
>> Thanks.
>>
>



Don't scuff them! You don't want to remove material, the problem is skin
oils or oils from the rubber that leach out and reduce the conductivity.
All you have to do is clean it thoroughly and it will work like new and
be fine for years.
From: Wild_Bill on 2 Feb 2010 08:37
I used to think that cleaning the conducive pads would solve key or button
problems, but the provblems returned quickly, several days to a week.
I tried using some of he milder solvens like 90% isopropyl alcohol and
denatured alcohol on swab tips, and may have even tried lacquer thinner, as
that would generally be my next choice. The problems kept returning.

For items like the rubbery button material in IR remote controls, the stuff
does get dirty and ooze oils from the plastic, but that was easy enough to
clean off.
Then I noticed all the faulty buttons conductive pads had a glossy
appearance identical to the pattern they're pressed against, so I gently
scuffed them just enuough to remove the shiney pattern, and they worked
perfectly for much longer periods.

They get shiney again after hundreds of presses, and when the faulty ones
were examined, they looked exactly the same as they did before they were
scuffed.
Buttons that are rarely used on keyboards, for example, keep working while
the most frequently used key conductive pads develop the glossy pattern.
After a very light scuffing, they work fine.

As I mentioned before, the very light scuffing procedure may involve just a
few passes across the conducive pad area, nothing any more severe than a few
brush strokes.

I'd still like to know of any recommendations for an effective conductive
paint-type product, for some of my older gear that I'd like to keep using
for many more years.

The best key switching design I've seen was on a vintage (maybe mid-1960s)
deskop calculator with Nixie tubes. The keyboard had a reed swich under each
key, and the hard keys had a small magnet in them.. very nice assembly, and
I expect that it was very reliable.

--
Cheers,
WB
..............


"James Sweet" <jamesrsweet(a)gmail.com> wrote in message
news:hk8jis$3r7$2(a)news.eternal-september.org...
>
> Don't scuff them! You don't want to remove material, the problem is skin
> oils or oils from the rubber that leach out and reduce the conductivity.
> All you have to do is clean it thoroughly and it will work like new and be
> fine for years.

From: James Sweet on 2 Feb 2010 21:39
Wild_Bill wrote:
> I used to think that cleaning the conducive pads would solve key or
> button problems, but the provblems returned quickly, several days to a
> week.
> I tried using some of he milder solvens like 90% isopropyl alcohol and
> denatured alcohol on swab tips, and may have even tried lacquer thinner,
> as that would generally be my next choice. The problems kept returning.
>
> For items like the rubbery button material in IR remote controls, the
> stuff does get dirty and ooze oils from the plastic, but that was easy
> enough to clean off.
> Then I noticed all the faulty buttons conductive pads had a glossy
> appearance identical to the pattern they're pressed against, so I gently
> scuffed them just enuough to remove the shiney pattern, and they worked
> perfectly for much longer periods.
>
> They get shiney again after hundreds of presses, and when the faulty
> ones were examined, they looked exactly the same as they did before they
> were scuffed.
> Buttons that are rarely used on keyboards, for example, keep working
> while the most frequently used key conductive pads develop the glossy
> pattern.
> After a very light scuffing, they work fine.
>
> As I mentioned before, the very light scuffing procedure may involve
> just a few passes across the conducive pad area, nothing any more severe
> than a few brush strokes.
>
> I'd still like to know of any recommendations for an effective
> conductive paint-type product, for some of my older gear that I'd like
> to keep using for many more years.
>
> The best key switching design I've seen was on a vintage (maybe
> mid-1960s) deskop calculator with Nixie tubes. The keyboard had a reed
> swich under each key, and the hard keys had a small magnet in them..
> very nice assembly, and I expect that it was very reliable.
>
> --
> Cheers,
> WB
> .............
>
>


I suppose the surface could wear over time, I've just never seen it
myself. Certainly try just cleaning before doing anything more drastic
though, liquid dish soap and warm water works as well as anything I've
tried.
From: Andy Cuffe on 3 Feb 2010 12:21
On Sun, 31 Jan 2010 13:33:24 -0800, mike <spamme0(a)go.com> wrote:


>
>Don't forget the calibration problem. Unless you have the procedure,
>the software, the gpib controller, and the specific calibration
>equipment, you may still end up with a scope that doesn't work.

Assuming your scope does work, it might not be a bad idea to backup
the contents of the Dallas NVRAM module. It has an internal lithium
battery that is only rated to last about 10 years. Since many of
these scopes are approaching 20 years old, they could fail at any
time.

I was able to read the NVRAM from my TDS544 using an EPROM programmer.
Hopefully, when the battery does fail, I will be able to replace the
battery, and reprogram it from my backup. When I read it, I tied the
WP pin to the VCC pin so that there was no chance of corrupting it.

Andy Cuffe

acuffe(a)gmail.com
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