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From: DaveC on 1 Feb 2010 04:03
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.

From: Wild_Bill on 1 Feb 2010 05:01
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.
>

From: JW on 1 Feb 2010 05:12
On Sun, 31 Jan 2010 12:49:09 -0800 DaveC <invalid(a)invalid.net> wrote in
Message id: <0001HW.C78B2CC50195EC48B0B2D9AF(a)news.eternal-september.org>:

>> All my experience is with the 540, but I think you're wasting your time
>> trying to troubleshoot ANYTHING
>
>OK, I suspected that, but non-functional buttons seemed a symptom not related
>to caps issue. But I'll take your advice to heart and do *all* the caps.
>
>> until you replace ALL, AND I DO MEAN
>> EVERY SINGLE ONE on every board, the caps and CLEAN
>> CLEAN CLEAN and CLEAN again the circuit boards.
>
>Yeah, I plan to do that. Making a complete list right now.
>
>What techniques and chemicals did you use?

I use Simple Green with a good non-metallic brush, then follow up with 90%
isopropyl alcohol. For the rubber membrane contacts VERY gently clean with
alcohol and pat dry.

On scope ACQ boards that have been badly contaminated I run 'em through
the dishwasher rinse cycle first with no soap. I position them vertically
which allows the sprayer to gut under the chips themselves, as well as
allowing the contaminant to run off. Then I put it in front of a fan for
an hour or so, after which I do the cleaning mentioned above.
From: JW on 1 Feb 2010 05:19
On Sun, 31 Jan 2010 14:14:59 -0800 mike <spamme0(a)go.com> wrote in Message
id: <hk4vf4$jdr$1(a)news.eternal-september.org>:

>DaveC wrote:
>>> All my experience is with the 540, but I think you're wasting your time
>>> trying to troubleshoot ANYTHING
>>
>> OK, I suspected that, but non-functional buttons seemed a symptom not related
>> to caps issue. But I'll take your advice to heart and do *all* the caps.
>>
>>> until you replace ALL, AND I DO MEAN
>>> EVERY SINGLE ONE on every board, the caps and CLEAN
>>> CLEAN CLEAN and CLEAN again the circuit boards.
>>
>> Yeah, I plan to do that. Making a complete list right now.
>>
>> What techniques and chemicals did you use?
>>
>> Thanks for your reply.
>> Dave
>>
>On the subject of technique.
>You have significant risk of lifting pads when you remove the old caps.
>The solder will be corroded. You need to "tin" each joint to expose
>clean solder for heat transfer.
>To remove caps, use two soldering irons. One on each end but on opposite
>sides.
>Gentle pressure provides a twisting motion that rotates
>the cap off the pads. This is MUCH less stressful to the pads than
>trying to pull upward on the cap.

I've had 100% success just using a pair of wire cutters. I cut the caps
off where they dimple in at the bottom, then use a probe to remove the
remaining metal and plastic bit. After that, a soldering iron to remove
the remaining leads. When I cut the caps, I keep the blades parallel to
the leads to avoid any more stress than necessary.
From: Nico Coesel on 1 Feb 2010 11:57
DaveC <invalid(a)invalid.net> wrote:

>This scope has the famous "FAIL ++ Acq" error which points to the infamous
>failed (and leaking) SMD caps on the acquisition PCB.
>
>I'm moving on to troubleshoot another (unrelated, I think -- and hope) issue.

Tektronix has an excellent user forum covering these sort of repairs.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico(a)nctdevpuntnl (punt=.)
--------------------------------------------------------------
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