I made a mistake restoring a Model M

damorgue · 07 Mar 2014, 23:07

I have boltmodded a few Model M's now, but this time I screwed up. It had exceptionally oxidized connectors on the ribbon cables, even after rubbing them they were still quite dirty. I just so happened to have a bottle of acetone right in front of me on the desk which I use to clean stuff with. So I thought why not throw some of that on there. Well, let's be honest, I didn't really think it through.

Soooo, anyway:

(To be honest, it removed the dirt very efficiently.)

Now here is the question. What is the best way yo fix it? I am quite certain I will have to wipe it in between the traces since I might otherwise short a few of the traces with the smudged conductive stuff.

Conductive ink
I think this runs a great risk of just getting rubbed of in the connector which is sort of mechanically abrasive to a relatively weak conductive ink. The coating might not be very flexible either and break up unlike conductive ink used on for instance a hard PCB.

Conductive tape
If I use tape which is only conductive in the Z direction then I might be able to just put a strip over it all. 3M has a quite famous such tape. Since the ribbon cable is single sided, all I really need is a conductive tape with conductive adhesive and I can cut thin strips and tape them over the edge. This will provide some mechanical durability as the tape can't be torn of ass easily by the connector. I might need to replace it each time the cable is unplugged, but that shouldn't be commonplace anyway.

Something else?

Compgeke · 07 Mar 2014, 23:23

It might be possible to find a bad Model M membrane and then cut half the ribbon off it and half off yours then solder the half from the bad membrane onto your good membrane.

While it sounds a bit intimidating it's similar to fixing motherboard traces after battery corrosion. All it takes is a steady soldering hand.

damorgue · 07 Mar 2014, 23:28

Well, the traces don't appear to be very metallic unlike all other ribbon cables I have encountered. I don't think the solder would wet well to these, and I don't know how the temperature might affect the plastic either which is why I eliminated solder. Thanks for the suggestion though, I will keep it in mind.

Muirium · 08 Mar 2014, 00:39

Looks pretty damn tricky. Rather than hybridise membranes, I'd just swap it wholesale if you have a donor M.

Did IBM often fiddle with the trace layout? I find my (one and only) 122 key's 2KRO quite maddening, because the mods weren't given precedence in the membrane's design. Not nearly as much a problem, fortunately, on my other smaller Ms.

webwit · 08 Mar 2014, 00:43

This is the kind of part Unicomp might have lying around.

scottc · 08 Mar 2014, 00:48

I have a spare membrane that's cut near the top if you're interested. It's no good to me as it is, but maybe my crap membrane combined with your crap membrane could bring your Model M back to life?

7bit · 08 Mar 2014, 00:50

Hi damorgue!

I don't much understand what the problem is, but I've got 2 innards of Model Ms (one IBM and one Lexmark). Let me know what you need.

damorgue · 08 Mar 2014, 01:27

Thanks for the offers, but I was sort of hoping that I could salvage this with either conductive ink or conductive tape.

Do you all think it is really that bad and beyond repair?

Muirium · 08 Mar 2014, 01:31

Beyond simple, sure repair. It's a critical point to fail at, and not the most costly of parts you'd think.

matt3o · 08 Mar 2014, 11:50

since the upper part of the traces are all intact I would definitely give conductive tape a try. Be sure to clean the connector carefully to prevent shorts. If that doesn't work... well just find a donor.

damorgue · 09 Mar 2014, 12:04

That was exactly my thoughts matt3o. It can't be that hard to fix, but I have since then changed my mind a bit. Although conductive ink/tape would probably work and not require me to undo the bolt mod, it is somewhat expensive. After checking around a bit, I haven't found any cheap sources for conductive ink/tape, mainly because they can't be bought in tiny amounts.

How much would a replacement layer cost me? I think it is the topmost, the one with the widest ribbon cable.

wheybags · 09 Mar 2014, 13:14

You can get a new membrane from unicomp for like $10

damorgue · 14 Mar 2014, 08:24

7bit wrote:Hi damorgue!

I don't much understand what the problem is, but I've got 2 innards of Model Ms (one IBM and one Lexmark). Let me know what you need.

Does anyone know if there are any differences is placement of rivet holes in different versions of the Model M?

cookie · 14 Mar 2014, 11:43

you could apply conductive paint and restore the connectors that way.
Maybe you could also mix superglue with dust from sanding metal parts, but first try conductivity on a test surface

E TwentyNine · 14 Mar 2014, 15:39

wheybags wrote:You can get a new membrane from unicomp for like $10

Note this is a complete membrane set, both layers and the dividing layer. If you're already done the bolt mod, and you're in the US so shipping is like $5, it's the best solution. Put it together, button it up, never worry about it again.

damorgue · 14 Mar 2014, 17:04

Yeah, I had it all screwed up together when I decided to clean the contacts. I am in EU, but I'll check with Unicomp if they can help. I could probably arrange a proxy if they want to be annoying.

7bit has offered innards but they will probably be expensive to ship with the plate, and a lot of work for him just to remove it for me.

phosphorglow · 15 Mar 2014, 02:32

I have to agree with using the conductive tape.

Also, it's nice to know acetone will strip away the traces. Did it start to eat the mylar?

Also also, pencil eraser and then isopropyl alcohol for future reference.

E TwentyNine · 15 Mar 2014, 02:45

It doesn't need to be the expensive copper tape. Aluminum foil tape, the kind used for some ductwork (no, not duct tape) is way cheaper and will get the job done. I know this because I've done it for a broken trace in a similar situation and while it's a little thicker, the connector where the membrane plugs in has plenty of give.

Of course I did order a membrane from Unicomp but I was too impatient in the meantime...

bitslasher · 15 Mar 2014, 06:48

As wheybags said earlier, you can easily get one for $10, new from the factory!

http://pckeyboard.com/page/Misc/MEM

damorgue · 15 Mar 2014, 17:23

damorgue wrote:
7bit wrote:Hi damorgue!

I don't much understand what the problem is, but I've got 2 innards of Model Ms (one IBM and one Lexmark). Let me know what you need.
Does anyone know if there are any differences is placement of rivet holes in different versions of the Model M?

This remains unanswered. If it doesn't fit the plate I will have to drill new holes in the plate as well as barrel frame. I can't think of a reason why they would have changed the positions of the rivets but they might have for some reason.

Unicomp wants some 24USD to ship it to Europe. They want 6USD to ship to the US. I wonder if a proxy could ship it for less than 18USD or if Unicomp might take a special request.

E TwentyNine wrote:It doesn't need to be the expensive copper tape. Aluminum foil tape, the kind used for some ductwork (no, not duct tape) is way cheaper and will get the job done. I know this because I've done it for a broken trace in a similar situation and while it's a little thicker, the connector where the membrane plugs in has plenty of give.

Of course I did order a membrane from Unicomp but I was too impatient in the meantime...

Do you perchance have an eBay link or 3M serial number for it? I have searched eBay but only the expensive ones explicitly mention conductive surface and conductive adhesive.

phosphorglow · 15 Mar 2014, 19:56

damorgue wrote: Do you perchance have an eBay link or 3M serial number for it? I have searched eBay but only the expensive ones explicitly mention conductive surface and conductive adhesive.

I've got a roll sitting here. It says:
3M 3340 III/13
UL181A-P
UL181B-FX
COLD WEATHER

phosphorglow · 15 Mar 2014, 19:58

(also works well as a heat shield if you ever do any BGA reflow work.)

phosphorglow · 15 Mar 2014, 20:04

Just tested the adhesive side with my ohm meter. Doesn't conduct very well unless you wipe it off with some acetone or scratch it off. If you use it, you'll have to come up with a creative method of affixing it to the traces. Perhaps folding it over?

phosphorglow · 15 Mar 2014, 20:08

OOOOH! IDEA!

The ribbons are longer than needed, so you might be able to chop off the ruined end and remove the conformal coating.

Only problem is removing the coating... ;P

damorgue · 17 Mar 2014, 15:21

Yeah, when they add conductive adhesive there is a jump in price it seems. There ought to be some cheapo Chinese manufacturer of it though if one can find itt.

phosphorglow wrote:OOOOH! IDEA!

The ribbons are longer than needed, so you might be able to chop off the ruined end and remove the conformal coating.

Only problem is removing the coating... ;P

I had this idea early on but I didn't think there was enough left. I guess I could insert it and check if it makes contact at least. It is free to try so I probably should give it a go before I go to other methods.

daedalus · 18 Mar 2014, 11:26

I've fixed this sort of stuff before using a silver conductive gel pen. However, if there isn't enough exposed trace, you may end up having to 'draw' a new trace on top of the ribbon all the way back to the membrane.

jeff · 18 Mar 2014, 21:02

I may advise "loctite 3863 circuit+", it's designed to repair car rear window defrosting system but is efficient for that kind of job.