A tutorial for preserving those mylar-based XL keyboards.

[Bryan]

Most 600/800XL computers come with a Stackpole-made folded mylar keyboard (Figure 1). Considering how budget-minded these keyboards are, they have a pretty good feel, but each one has a little time-bomb ticking inside.

 

Contact is made via a conductive metallic paint applied to a mylar sheet which is folded in half. A small spring under each key pushes the top layer of mylar against the bottom layer whenever a key is pressed. The problem is that the paint oxidizes when exposed to air. Eventually contact is lost and the mylar sheet must be replaced.

 

This damage can be prevented (or halted), however, with a simple procedure. You will need a couple Philips screwdrivers (larger one for the case, and a small one for the keyboard), a can of Acrylic Enamel spraypaint, masking tape, large piece of cardboard, paper towels, glass cleaner, a pencil eraser, white lithium grease, and a cotton swab.

 

To identify your keyboard type, look into the thin gap around the keyboard (it's usually easiest to look around the space bar). If you see a silver-metallic keyboard assembly, you have a mylar-based unit. If you see brown, black or green you have a PCB-based keyboard (yay!), and you don't need to do anything.

 

Step 1: Remove the keyboard from the computer.

 

Start by removing the case screws (keep your hardware organized for proper reassembly). Gently lift the top and unplug the keyboard ribbon connector. (If this ribbon is NOT made of transparent plastic, then you don't have a mylar keyboard). Turn the top case upside down and remove the 4 large keyboard screws (One may have a wire connected to the cartridge door, just leave it connected at the other end). You should now have a keyboard that looks like Figure 1.

 

Step 2: Disassemble the keyboard.

 

With the keyboard face-down. Remove all the small screws from the back and separate the metal back and mylar sheets from the keyboard. There are 2 key assemblies, one for the main keyboard, and one for the function keys. DO NOT turn the black keyboard assemblies over, as each key has a small spring under it that will fall out. Make sure every key has a spring when you finish. (Figure 2)

 

It is a good idea to wash your hands to remove any excess oil at this time.

 

Step 3: Affix the mylar.

 

Set the smaller separator sheet aside.

 

Carefully tape the mylar down (contact side up) to the cardboard at the corners. Do not force the mylar completely flat at the crease (or you may damage the paint at the bend) and do not cover up any of the paint traces with the tape. Apply glass cleaner to a paper towel, and gently wipe the mylar clean. (Figure 3)

 

You'll probably notice a good bit of oxidation damage already. Don't worry, as long as there's enough good paint left to make contact, the keyboard will work.

 

Step 4: Prep the mylar.

 

Apply tape to all contacts. This can be done in strips as shown, or with individual pieces of tape if you're a perfectionist/masochist. Be sure to cover the following (Figure 4):

 

All key contact circles top & bottom including the space bar.

All function key contacts top & bottom.

The 2 LED contacts in the corner.

The insertion portion (last 1/4") of the ribbon connector.

Also cover the clear ribbon flap (the ribbon with no contacts - shown covered in Figure 5).

 

Step 5: Paint the mylar.

 

Apply a light coat of paint to the mylar. Use enough to evenly cover, but not more than 1 coat. The purpose is simply to keep air from destroying any more of the metallic paint. Allow the paint to dry. (Figure 5)

 

Step 6: Remove the tape.

 

Carefully remove all the tape. Do not use any sharp objects to lift the tape, since it may cause damage to the painted traces. Wipe the mylar clean with glass cleaner again. (Figure 6)

 

Step 7: Reassemble the keyboard - part 1.

 

Verify once again that all contact springs are in place.

 

Remove the mylar from the cardboard and refold with the separator sheet in the middle. Align the holes and place the mylar over the raised guide bumps on the back of the keyboard assembly. When everything is aligned, place the metal plate on the back and replace the small screws for the main part of the keyboard. Once the back is on, flip the keyboard over.

 

Step 8: Treat the contact areas.

 

8a - If they are dark from oxidation:

 

Using the pencil eraser, gently rub the insertion portion of the contact side of the ribbon connector. It should turn lighter silver in color, but it is not necessary to make it completely white. Do the same to the LED contact squares. Gently blow/wipe away all eraser mess.

 

8b- Protect the exposed areas:

 

Using a small amount of White Lithium Grease on a cotton swab, apply a thin film of grease to the LED contact squares and the insertion contacts. Grease film should appear clear. Remove any extra grease. This will prevent contact with the air, but still allow electrical contact. (Figure 7)

 

Step 9: Finish assembling the keyboard.

 

Turn the keyboard back upside down and carefully align the raised guide bumps in the function key assembly with the mylar sheet, then align with the holes in the metal plate (This is tricky because there is excess length in the mylar which will try to push the function key assembly away from the holes, and watch for falling springs again!). Once everything is aligned, replace the screws to the function key section. (Figure

 

Using some tape at the edge, affix the loose cover ribbon to the main contact ribbon.

 

Step 10: Reassemble computer.

 

Put the keyboard back into the top case and replace the screws (and the wire, if present). Make sure the keyboard is centered in the opening and the function keys move freely. With the top case propped up vertical to the bottom case, gently insert the ribbon connector using both hands, by pinching it at both sides very near the bottom. It should slide down and stop. Replace the top case and case screws.

 

Step 11: Run the Keyboard Test from the Self-Test menu.

 

If all is well, every key except BREAK should respond to the test. BREAK is easily tested from within BASIC. If a key does not respond, check for clean contacts, proper ribbon insertion, and loose springs lying around.

 

Your keyboard should now last a VERY long time.

 

-Bry

[Bryan]

Rest of the pics:

[oesii]

I just had the left-side SHIFT and CONTROL keys stop working on my 130XE. Do they have a similar mylar like the 800xl?

 

I already took the keycaps off and the springs and plastic pieces all looked fine. So now I have to dig into the case and check the mylar

[Bryan]

There are 2 different XE keyboards that I know of, but they both use mylar contact sheets. One is folded like the XL one above, and one is a single sheet.

 

-Bry

[svenski]

1200XL keyboards are notorious for this sort of problem.

 

Last time I tried a fix I ended up with one more key working

 

Still wasn't as professional as your tutorial though, will have another go.

[Bryan]

I've never seen a 1200XL keyboard that uses mylar sheets. The ones I've seen use a PCB and carbonized rubber under the keys.

 

-Bry

[svenski]

Definitely mylars on all the 1200XL keyboards I've looked at.

 

I know Best sell replacements for the 130XE but apparently they never had enough demand for a 1200XL one.

[svenski]

Have attached a link to a 1200XL keyboard "tune up", written by Bob Woolley.

 

The 1200XL mylars tend to lift off the pcb over time, especially if someone gets fluid between the keys.

 

I didn't have much success with this method, had better luck not removing the mylar and sitting on the pcb , but others more skilled in the arts of Atari have .

 

http://retrobits.net/keyboard.html

 

Obviously a 1200XL mylar is a bit different from a 800XL one - not folded for starters.

[Bryan]

I'm gonna have to take out my 1200XL and look at it.

 

-Bry

[krupkaj]

I just had the left-side SHIFT and CONTROL keys stop working on my 130XE.  Do they have a similar mylar like the 800xl?  

 

XE keyboard has mylar inside too. But it has only one layer and keys uses springs with conductive rubber. ST has the same keyboard.

[dinosaur]

In my couple of decades of Atari devotion,I have never tried to repair

a keyboard.....

 

Question:

 

I have a nice 1200XL that has a broken (off) keycap.

(something was dropped on it! Grrrr!)

 

Can I replce this keycap with one from a dead 800XL?

 

Thanks.