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1200XL Keyboard Issues


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I recently added a nice looking 1200XL to my collection. Unfortunately, the keyboard doesn't seem to work.

 

I testing it with just the BASIC cartridge installed. I then tested it with a couple of game cartridges (Galaxian, Jungle Hunt). I then tested with no cartridge, attempting to press the HELP key to enter the self-test mode.

 

The only keys/function keys that appear to work are the "2" and the "Tab". Both of these keys work with BASIC installed. No other keys or function keys appear to work.

 

I did disconnect the keyboard connector and the LED connector and reseat them.

 

Any suggestions before I take it apart further.

 

Regards,

Bill

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Follow the Retrobits text and you will be OK.

 

Currently, I use Bare Paint, a conductive, water-based coating. I also run 1/32" map tape between the fingers so I don't get shorts.

 

You don't want the paint too smooth. Peel off the map tape after the paint dries some.

 

You can remove the key frame and press keys with your fingers, if you want to see POKEY respond. Just press one finger across the connector and another on a key.

 

Bob

 

All 1200XL keyboards fail like this, for the most part.

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I've done a few of these now and I am unconvinced that the problem in most cases is the carbon trace contact array that is shown in Figure 3 and 4 of the Retrobits article.

 

In the last two machines I have restored, I have unpeeled the mylar key matrix from the circuit board, but not enough to break the contact array, and then essentially re-seated it by using electrical tape on the edges to get as tight a fit as I can. My best guess is that the key contact points on the mylar wear out, but in a highly focused area. The tiny adjustment made by un-peelign and re-seating the mylar moves the point of contact just enough to allow the keyboard to work again.

 

Has anyone else experienced this?

Edited by oracle_jedi
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I removed the mylar, clean the board with windex. I then cleaned the suspect area with Goo-gone and then windex. I taped the suspect area with scotch tape. Once all the screws were reinserted and tightened (especially the two on either side of the suspect area), it seems to work fine.

 

I ordered the silver paint and will probably apply that as well next week.

 

Thanks for the help.

 

Now on to fixing the sio port and the monitor output.

 

Bill

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I was always impressed with the look and feel of the 1200XL keyboard, and it seemed to be quite robust. Never realized that underneath it was just mylar and flexible circuit traces. But it does make sense considering the very reasonable pricing compared to the 800 that preceeded it. However good thing there is a fix, since I would imagine these things are getting rather scarce (how many 1200XLs were built?).

 

BTW; you did a great, or should I say fantastic job with that repair tutorial Bob.

Edited by mytekcontrols
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Bob's is the definitive solution to a universal, inevitable problem. Every 1200XL keyboard I saw had the issue, and Bob's fix, followed to the letter, solved the issue every time. One thing I found useful is a couple of bits of electrician tape of the back side of the Mylar where the plastic lip between the two retaining screws presses it into place. The tape increases compression a bit and makes for good contact.

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I have had some success with just repositioning the mylar on the PCB or cleaning the contacts or adding pressure to the connector with tape. But, none of these 'fixes' will work consistently or permanently, in my experience. Clean the gold contacts with 98% alcohol and paint the connector fingers.

 

Bare paint seems to be superior to silver paint.

 

Bob

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Bob, I think the conductive paint I've been using (in a little phial, requiring much shaking before use) is a little thin and had occasional trouble even after the contacts had been cleaned until I added the tape on the back. But I should imagine better quality paint would be a superior solution, exactly as you say.

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There is a bar molded into the key frame that compresses the connector when you screw it together. If you add tape to this bar and close up the keyboard, it may work for a while, but the tape will expand/compress to the shape of the fingers leaving you with poorly compressed contacts. I even tried 1/32" map tape, applied only on the contact surface - didn't hold up. It seems that anything 'soft' just creeps away and anything 'hard' is inherently uneven.

 

The idea behind the paint is to produce a 'lumpy' surface that will contact the mylar outside the circumference of the bar. This turns the mylar itself into a 'spring' that holds the contact in place.

 

Lumpy is good...

 

Bob

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