Sega SC-3000 Keyboard Repair / CW2605 Keypad Repair kit

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Sega SC-3000 Keyboard Repair / CW2605 Keypad Repair kit

Postby honestbob on Thu Sep 12, 2013 10:56 am

Hi All

Sorry if I've posted these before, but I took a quick look and I don't think I have. Here's a little repair job I did over Winter which might be useful for other old 8-bit micros (or your TV remote control).

The original Sega SC-3000 has a rubber keyboard, and to be honest they were terribly unreliable even when new back in 1984. I think the correct term is 'chiclet'. Basically it has a circuit board with big pads where the two halves of the circuit are seperated for each key, and underneath each of the rubber keys there is a conductive rubber pad. When you press a key, the conductive rubber pad contacts the PCB underneath, and closes the circuit. I believe several other 8-bit micros used a similar keyboard design, and you will still find a lot of TV remotes and cell phones using this design too.

The problem is that over time, the rubber pads on the underside of the keys gradually lose their conductivity (or their coating, if the rubber was only coated rather than doped). I forget exactly, but you will probably find a brand new conductive rubber contact has something like about 50 to 200 ohms resistance. But over time that may climb to several thousand ohms. Then your keyboard becomes very unreliable.

There are lots of ways to fix these keyboards. You can try cleaning the pads, you can glue little cut-out circles of tin foil to them etc. But there are good permanent fixes available.

I repaired mine with a Circuitworks CW2605 Rubber Keypad Repair kit (I bought my CW2605 kit off eBay).

http://www.chemtronics.com/products/pro ... &m=2&id=32

It worked really well. The kit says it has enough to repair 50 keys, but I did two full SC-3000 keyboards with it and I probably had enough silver epoxy for a third keyboard. Just use a *very* thin coat on each key, and remember you only have a max of about 2-3 days to use the product once you mix part A and part B, so that is its only real drawback. I tried leaving it 24 hours after mixing before doing the second keyboard and the mixture was still usable, although definitely a bit firmer than the day before. (I also gently cleaned down the PCB contacts with isopropyl alcohol and a cotton bud).

This is a professional repair product which is supposedly tested to 500,000 keypresses, so it should not flake off over time. Unfortunately it is a bit expensive to import for a one-off repair job, so I suggest you wait until you have several keyboards to repair before getting it.

Note - I also tried doing one of the keys using a conductive silver pen. That seemed to work quite well too, so that could be a viable alternative. I don't know how flake resistant that is by comparison though, and the conductive silver pen didn't spread quite as neatly over the contact as the CircuitWorks kit did.

In any case, all the keys work brilliantly now. You just need a light touch to activate them. See photos below.

Does anyone else have any favourite repair techniques for this style of keyboard?

Cheers

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Re: Sega SC-3000 Keyboard Repair / CW2605 Keypad Repair kit

Postby tezza on Thu Sep 12, 2013 12:15 pm

That's a great repair tip. Thanks for posting.
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Re: Sega SC-3000 Keyboard Repair / CW2605 Keypad Repair kit

Postby Omcsesz on Sat Apr 15, 2017 11:20 pm

The webpage of the product has been changed.
https://www.chemtronics.com/p-713-circu ... r-kit.aspx
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