To: analogue@hyperreal.org,
From: "Bob K" shibuyamorning@verizon.net,
cc:
Subject: [AH] slider cleaning (was: scratchy sliders- clean or replace?)
Date: Tue, 25 May 2004 23:36:19 -0400
Regards to Andrew's question about cleaning sliders, I want to forward a
conversation that Kevin Lightner and I had last October regarding =
servicing
my Opus 3 sliders. I sent this email to the list many months ago but =
want
to do it again... mainly for archive purposes.
I asked Kevin's permission to post this to the list a while ago, and he
agreed to make our conversation public.
-Bob
..................
>Hi Kevin,
>
>Regarding replacing one slider and cleaning the rest, are you =
suggesting
>that I remove the sliders and actually run the pcb under a faucet to
>clean it? Won't water damage the circuitry? If I do run the board
>under a faucet, should I use a soft-bristled toothbrush of sorts as
>well?
>
>A few months ago I removed the cover and cleaned off the oxidized
>insulation, that had turned into black goo, with q-tips. Running the
>pcb under water will help?
>
>If I remove the sliders, are they easy to pop back into place?
>
>I hope you don't mind the many questions as I'm pretty sure you get
>loads of emails like this, but I just want to be sure I have all of my
>bases covered before I go into this project.
>
>Thanks for the advice so far.
Hi Bob,
Hope this doesn't come off sounding too self-absorbed, but it's not=20
easy to note what *I* do without using the *I* word often.... ;-)
I do wash boards, though I've a few precautions and practices well down.
For me, I use high pressure softened water and usually a good grease=20
cutting detergent.
I prefer SimpleGreen for this as it's biodegradeable and easily =
available.
Also De-SolvIt is great, but is oily and it itself must be removed=20
with simplegreen as well.
I don't allow things to soak too long, but 3-5 minutes immersion is=20
usually needed to dislodge old grease.
After a rinse, the boards are blown using compressed air and placed=20
in a forced air dryer.
A hair dryer (not too hot) will substitute fine. Allow them to sit=20
overnight before powering up.
Boards are often washed when originally made and soldering, both by=20
hand or machine, exposes a board to higher temperatures than any=20
water you'll handle, even boiling. The main thing is that water is=20
not left to dry and leave mineral deposits or react with metals to=20
oxidize (rust, aluminum oxide, lead oxide, etc). The only components=20
that have ever acted up, and rarely at that, are the larger foil=20
wound caps found in CV memory circuits such as key memory and sample=20
and holds. I replace them if so, but out of about 30-50 Odys that=20
have received this treatment, only 2 needed components replaced.=20
Those odds are well within my confidence range considering the=20
positive results otherwise.
One plus about this technique is that it removes coatings on the pcb=20
that can degrade audio and CV's.
It's quite common to have things more stable and of better fidelity=20
after a total cleaning.
Sample and hold circuits can droop simply from body oils on a board.
Imagine what 28 years of atmospheric junk can do when accumulated.
After washing, most sliders feel much better, but keep in mind that=20
immediately afterwards they are still wet inside and will still feel=20
lubricated. After drying, they will need new lube. I use GC=20
Electronics Luberex and apply it through a hypodermic syringe. It=20
helps to remove and disasemble one slider so as to give you an idea=20
what points require lube the most. Lube on the resistive element=20
generally won't hurt it or affect its operation, so you don't have to=20
be ultra careful. I will also use a drop or two of TriFlow Teflon=20
lube if they need to be a bit less frictional. It's all on a "as=20
needed" basis, so I'm hesitant to provide any blanket rules or offer=20
this as the bible of slider repairs. This is what has worked for me=20
and is proven over time.
The sliders are not terribly easy to remove nor to replace the shafts.
You must remove the entire slider in order to swap the shafts also.
I really don't know how to detail what's involved if you've never=20
done the operation before.
Like teaching guitar via email: I could take apart 20 sliders in the=20
time it took to write this email, but it took years of doing and with=20
many failures that taught valuable lessons. I would recommend some=20
smooth jawed flat pliers and whatever you feel comfortable with for=20
desoldering. If I didn't use power desolderers, my next choice would=20
be solderwick. The little bulb or piston solder suckers just don't=20
cut it for me. More pain than they're worth.
When I use or offer sliders for sale, they are made up of selected=20
parts from several sliders.
Often the tops are hand polished to get them smooth again and remove
scratches.
The inside wiper plate and contacts are polished using swabs and chrome
polish.
They're solvent cleaned and relubed, then assembled, checked for=20
proper tension and then bench tested using an audio generator and=20
scope. Lots of work for sure. The payoff for me (besides the money)=20
is getting an Arp to feel almost brand new. Many people have no idea=20
how nice they can usually turn out.
They've never played a new one.
Also, I very much recommend on any gear, a very close inspection=20
under bright light.
Solder connections, especially on larger pins and connections, or=20
leads of items that are subject to physical force are the most common=20
places. Pins that carry high current or experience higher=20
temperatures are subject to premature cracking as well.
I do this operation to *every* board of *every* unit that comes in=20
here. No exceptions.
It's that important. The pcb is the most important component and=20
makes the most connections.
So many repairs I and other techs do everyday is nothing more than=20
resoldering cracked pcb connections.
On some units, I won't even power them up until this is done. For=20
example, the display board of the Roland S-50 is sooo often filled=20
with cracked connections, it's assumed that's needed everytime. After=20
a while, one gets savvy where to look and what to touch up. My secret=20
weapon to not seeing any rework ;-)
Hope this helps!
--=20
Regards,
Kevin Lightner
http://www.synthfool.comBR>
-----Original Message-----
From: Enmach@aol.com [Enmach@aol.com]=20to:Enmach@aol.com]=20
Sent: Tuesday, May 25, 2004 11:21 PM
To: ahorton@vt.edu; analogue@hyperreal.org
Subject: Re: [AH] scratchy sliders- clean or replace?
If the defect can be diminished by repeatedly exercising the slider, =
chances
are that the problem can be cured with a thorough cleaning.
If the scratchiness shows no signs of abating after vigorous use (or =
gets
worse), there's the possibility that the part has become corroded and is =
in
need of replacing.
If I may be so nosey, who have you decided on for service? Your recent =
post
got a number of responses...
Pat=20
In a message dated 5/25/2004 11:01:27 PM Eastern Daylight Time,
ahorton@vt.edu writes:
=20
> My free System 100 that I'm about to put in the shop has the classic=20
> "scratchy
> sliders" - a few of the sliders, especially those that directly affect =
the
> sound (like filter cutoff) make staticky "scratching" sounds when =
moved.
>=20
> What's the deal with scratchy sliders- is it just a contact point that =
> needs
> to be cleaned, or is it a corrosion/defect that=20
> necessitates replacing the=20
> sliders?
>=20
> andrew