[sdiy] Chroma Polaris Switches - Follow up Report

[Glen]

At 07:19 AM 7/29/04 , Tony Clark wrote:

>   What I did to mine was to cut the ribbon cable where the crack 
>occured.  Then use a sharp knife to scrape off the protective layer 
>covering the traces.  If done correctly, you can actually solder directly 
>to these traces.  if this is too difficult, you can utilize a conductive 
>epoxy to attach normal wires to these points.

I think I've found a better way. Here's what I've done to mine so far:

Cut off the cracked piece of the membrane ribbon cable, just as you did.

I also trimmed off some of the clear plastic which is layered loosely over
the ribbon cable, to relieve some stress on the conductive ribbon.

Instead of scraping off the green insulating coating with a knife, I
removed it by wiping it off with a paper towel soaked with PEC-12 (a
Photographic Emulsion Cleaner). Although PEC-12 is designed to clean
stubborn smudges and deposits from photographic film, it really smells
suspiciously like some automotive paint thinner my dad used to use. (He
used to do auto-body repair for a living.) If you use the right type of
paint thinner, that should probably work also. Be careful, because not all
paint thinners would give the same results. Some types might melt the
plastic substrate, or perhaps remove the conductive traces. All I can say
for sure is, PEC-12 does an *EXCELLENT* job--even if it was never intended
for this.  :)

I removed the ribbon connectors from the PCB, and extended them with pieces
of "normal" ribbon cable. (The good ribbon cable, not this membrane stuff.)
So, I had the connectors reattached at the ends of ribbon cable "extension
cables".

After I had prepped the membrane ribbons, and extended the connectors, I
simply reassembled everything. I made sure that the membrane ribbons were
laying flat, with no physical stress exerted on them. The extended
connectors were perfect for allowing this.

The end result of the membrane restoration procedure was a total
success--at least as far as the membranes themselves is concerned. I did
find out that one connector needs replacement. Three pins are not making
proper connection. This results in 7 of the switches not responding from
the front panel. Fortunately, I can control these functions remotely, from
a MIDI knob box. At least I'm not deprived of actually using any of the
capability of the synth--(as long as I use the knob box.) If I had a new
connector laying around, I'd replace the current one, but I don't have a
new connector. It isn't a big deal to me, as long as I can control the
missing functions remotely.

I tried soldering to a scrap piece of ribbon, as Tony suggested, but I do
not recommend this idea. Any time I had solder hot enough to melt, it was
also hot enough to melt the plastic membrane, warping it badly, and melting
off the conductive trace as well. If Tony can actually solder to this
plastic surface, I'd like to know more about his technique. I would
recommend the average person to NOT use solder. At the very least,
experiment on one of the scraps you cut off the membrane ribbon first. 

I would be much more inclined to try the conductive epoxy method, but I
would certainly experiment on a scrap piece of ribbon first. Before I even
tried the epoxy, I would suggest simply extending the original connectors,
as I did. That might be all you need to do.

As for scraping off the insulating coating with a knife, this is also
risky. It can work, but it's too easy to scrape off too much, and scrape
away your conductive traces along with the insulating paint that covers
them. I can very highly recommend using a paper towel wetted with PEC-12 to
remove the insulating paint. This leaves the conductive traces totally
intact, and simply removes the insulating paint.

Like I said, PEC-12 is probably similar to some type of paint thinner, but
I don't know what type. If you want to fix a Polaris, and want to play it
safe, just buy some PEC-12 from a professional photographic supply company,
such as Calumet Photographic. (That's where I bought my PEC-12.)

  http://www.calumetphoto.com

----------------------------------------------------------

At this point, I have a Polaris that functions well enough for my needs
(with the aforementioned knob box helping out occasionally, when creating
new patches.)

However, I'm still going to be working on some sort of system to replace
the membranes with something better. At least I have bought myself some
time with this latest repair.

I want to thank Tony for encouraging me to try fixing the membranes. I had
done this sort of thing in the past, but I'm getting tired of doing it. I
guess my frustration with the whole membrane concept was making me want to
give up too easily.


thanks again,
Glen Berry