1200XL keyboard repair options?

[Smokeless Joe]

I followed Bob's excellent instructions at http://www.retrobits.net/atari/keyboard.shtml on two 1200XL keyboards. One is 100%, so hooray! The other keyboard, not so much. The reset button and buttons beyond no longer work (they did before).

 

[picture borrowed from site linked above]

 

All green parts have continuity, all blue parts have continuity, but green and blue do not have continuity, so the problem is somewhere in red.

 

Any ideas? Does anyone sell replacement mylar? Anyplace that might be able to make a custom one?

 

Thanks,

 

-Joe

Edited February 21, 2016 by Smokeless Joe

[Kyle22]

. . . Does anyone sell replacement mylar?

 

not yet.

[+DrVenkman]

 

not yet.

 

 

This sounds promising!!!! #tease

[+bob1200xl]

It looks like your trace is broken. You should be able to repair it with conductive paint - you just need to find where it fails and fix it.

 

The main question is what paint to use. I have been using these two paints, with varying success. The Bare paint is thick and make better contact than the thin Nickel paint, but the Bare paint is not very conductive. You will find a resistance of hundreds of ohms with the Bare paint, which may be OK if the rest of the circuit is low resistance, not so good if it isn't. The Nickel paint has very low resistance, but is thin and does not make good contact at the connector. You need a couple of coats with the Nickel paint.

 

I run 1/32" map tape between the contacts on the connector, lay down a couple of coats of Nickel paint and cross my fingers.

 

Bob

 

[+mytek]

It looks like your trace is broken. You should be able to repair it with conductive paint - you just need to find where it fails and fix it.

 

The main question is what paint to use. I have been using these two paints, with varying success. The Bare paint is thick and make better contact than the thin Nickel paint, but the Bare paint is not very conductive. You will find a resistance of hundreds of ohms with the Bare paint, which may be OK if the rest of the circuit is low resistance, not so good if it isn't. The Nickel paint has very low resistance, but is thin and does not make good contact at the connector. You need a couple of coats with the Nickel paint.

 

I run 1/32" map tape between the contacts on the connector, lay down a couple of coats of Nickel paint and cross my fingers.

 

Bob

 

DSC01538.JPG

 

Hi Bob,

 

What about using both? Paint with the one that makes good adhesion first and then use the nickel paint over that. Kinda like an insurance policy that something will conduct the signal through.

 

- Michael

[+bob1200xl]

It isn't adhesion - it's thickness - contact area.

 

The Nickel is solvent-based and won't play well with the water-based, Bare paint.

 

Probably best to use multiple Nickel layers.

 

Bob

[ACML]

It looks like your trace is broken.

I second Bob's diagnosis. I've repaired over a dozen 1200XL keyboards and sometimes one or more of the traces gets broken when you separate the mylar from the PCB. Just use your multimeter checking for continuity between the the black and red leads, but march down the trace in very small increments (like 1/4"). That will narrow down the break to a small spot. Apply the conductive paint, let dry, then try. Remember the broken trace can be under the white silicon spacer so you may have to peel back some white silicon to find the break. I've been using Bare Paint with great success, but Bob is right, is has some resistance. Enough so that a multimeter may not show continuity over the new painted bridge, but after drying, the keyboard will still work.

Edited February 24, 2016 by ACML

[Smokeless Joe]

Okay, this is reassuring. I'm using Bare paint and having a hard time seeing continuity. I've also been really reluctant to peel back the white silicone since it seems to always take some carbon trace with it, but I've got plenty of paint. I'll give it a try and report back. Thanks!

Edited February 24, 2016 by Smokeless Joe

[Smokeless Joe]

Partial success! Peeling back the silicone revealed an obvious break in the trace. A little Bare paint, a couple hours waiting, and now Reset, Start, Select and Option all work again. Hooray!

 

The only reason this is not a total success is because now I discovered the clr/set/tab through Y keys don't work. That's easy enough to trace, but now continuity goes all the way to the very top of the gold contacts, like this:

 

 

I just repainted the part that touches the gold contacts. It was a pretty uneven paint job. Now I wait.

[Smokeless Joe]

Complete success! Looks like that last little bit of paint did it. I now have two 1200XL keyboards that work!

 

Many thanks to Bob for his instructions and to ACML for the encouragement to not give up!

 

I'd still buy half a dozen new mylars, if someone were to make them.

 

-Joe

Edited February 28, 2016 by Smokeless Joe

[ACML]

Partial success! The only reason this is not a total success is because now I discovered the clr/set/tab through Y keys don't work. That's easy enough to trace, but now continuity goes all the way to the very top of the gold contacts, like this:

 

keyboard2.jpg

 

I just repainted the part that touches the gold contacts. It was a pretty uneven paint job. Now I wait.

Nice job! I've had this happen to me more than once, the trace goes all the way to the terminal end, but does not work assembled. That's because that one terminal pad didn't have enough paint built up (height) compared to the ones adjacent on both sides. As you've already figured out, you just have to add a little more paint to get the height up enough to make continuity once re-assembled.

Edited February 29, 2016 by ACML

[rockdoc2010]

I have repaired two mylar keyboards based on BOB instructions. The trick is to be very slow and don't damage any more than what is already damaged. I have found that the silver based ink is a biotch to work with! there is a product that is carbon based and is easy to apply as well as easy to trim. It dries more solid and can be trimmed with an exacto so much better.

In addition if you can work with solder, i was able to place solder nubs upon the upper and lower pads in order to get a good connection. this was done upon the solder pads that the mylar presses against when you reassemble the unit.

I will have to find the photos for the task but if you cant solder than it wont matter.

I suggest using the carbon based fluid.

the product is called Bare Conductive Electric Paint Bareconductive.com

 

Cheers it worked great for my repair

 

Be carefull!!!!! the mylar may tear

[rockdoc2010]

In other words, I fully removed the mylar, cleaned the pads, resoldered and cleaned the pads, added a solder nub and retraced the tear or loss of traces.

[rockdoc2010]

When you use a conductive trace, there may be a bit of resistance via the length of the trace. I am not sure in this case. The matching mylar sheets need a good connection and when you remove that minor sheet of cardboard you may lose a bit of pressure between the two sheets. I have found that a nub of solder placed properly on the upper and lower pad would help.

 

 

Sorry photo load kills the upload

[Sincity]

Complete success! Looks like that last little bit of paint did it. I now have two 1200XL keyboards that work!

 

Many thanks to Bob for his instructions and to ACML for the encouragement to not give up!

 

I'd still buy half a dozen new mylars, if someone were to make them.

 

-Joe

Best Electronics sells a replacement mylar.

[Xebec]

http://www.best-electronics-ca.com/1200XL%20keyboard%20Mylar.htm

 

There's the Mylar from Best. I'm in the process of ordering 1 (have 2 x 1200XLs with bad keyboards). Looks like it was a one time production run that Best did..

[+DrVenkman]

Best Electronics sells a replacement mylar.

 

They do NOW. I don't know that they were available a 17 months ago (which was when the comment you replied to was made).

 

FWIW, I've used Bob's fix on two 1200XL's, both done three years ago now. Both still work great.

[Sincity]

I have done Bob's fix once and again recently on the same XL. I think all of us should buy a spare mylar for the long run.

[DavidMil]

I bought one of Best's replacement Mylar's and my 1200XL keyboard works perfectly now. They are a little pricey as they have gold contacts

but they are guaranteed for life. Be sure you follow the online instructions for replacement!

 

DavidMil

[+kheller2]

Repaired two 1200XL keyboards today. That makes me want to go repair a few more I have! One was pretty easy to repair with a nickel pen, the other.. well.. the other was a very old 1982 PILOT unit and that mylar tore like tissue paper -- not only around the screw holes but just random places as well. I had zero hope of it working as almost all the carbon traces on the connecting section were gone. Nickel pen worked fine, I just had to make sure I got as much of the trace left as possible.

 

What have you done for your 1200XL today? HAH

[+DrVenkman]

Congrats!

 

That reminds me ... I have a brand new keyboard mechanism that I need to swap out for one missing a key on one of my 1200XLs. Well, I need to swap the mylar from the broken one to the new one, but along the way I need to repair the traces. That'll be a project for a rainy weekend in the coming months.

[ACML]

 

What have you done for your 1200XL today? HAH

I repaired three 1200XL keyboards last month and I have one to do tomorrow. I use "Bare" conductive paint and apply it with a toothpick. Its thinker than the circuit writer pen, but goes on nicely with a toothpick. I find that the toothpick allows more control. I paid $10 for a small tube of Bare conductive paint and I think I've repaired 12+ keyboards with it. I have seen the Best new mylars, but right now, I have no need for them. I have yet to come across a 1200XL mylar that could not be fixed with conductive paint. If Atari or Mitsumi didn't put the 1/4" x 2" tape between the gold PCB traces and the mylar, they all probably still work fine today. I know why they added it. They wanted to insure that there was good contact (pressure) on the pads so they built it up with that tape. What they did not understand was that that tape would oxidize the carbon material and eventually cause an open (the exact reason they put it in to avoid). How were they to know it would take 20 years to show up as a defect.