Trouble installing Best 1200XL mylar

[electronizer]

I'm trying to restore the 1200XL I found in the trash years ago. The keyboard was nonfunctional, so I ordered a replacement Mylar from Best. I cleaned the PCB and key caps, reinstalled everything, and...nothing. Just the reset key and maybe one other key worked. I installed the included thin wafer with gold contacts that goes between the Mylar and the PCB and this time, the O key was stuck on; a few other keys worked but not many.

 

Best says not to remove the layer of carbon that's built up over the gold PCB contacts that make a connection with the circuit traces on the Mylar, but I'm wondering if that's the weak link in the equation. Any suggestions for what to try next?

[+bob1200xl]

I have done about 10 of these and, on all of them, I cleaned the gold fingers on the k/b PCB with "Goof Off". I never use the little pcb that comes with the mylar. Leave the little foam piece added to the mylar alone. In fact, don't do anything to the new mylar.

 

I had one k/b come out dead. Opened it up and wiped the finger contacts on both the mylar and PCB with alcohol. All better, now.

 

Bob

[toddtmw]

I didn't wipe the traces on the board and I used the little add-in baord and did not have any issues.

 

Is it possible, you have another issue with the keyboard? Don't suppose you have another 1200 laying around?

[BillC]

If you have an issue you should try contacting Brad first, then post here if that doesn't resolve the problem.

[flashjazzcat]

What's the arrangement with the add-in board? I'm having trouble visualising why it's needed.

[toddtmw]

From the best web site:

When Best received the 3rd version prototype physical samples to run functional tests on, it was found that none of the 3rd version prototype 1200XL Mylars did not function at all. Even though our Keyboard manufacture used current 2016 state of the Keyboard mylar Technology to produce 3rd version 1200XL Keyboard mylar, it did not work in the 25+ year older technology Atari 1200XL Keyboard design. After studying this non functioning 3rd Prototype samples for a week or more, Best came to the conclusion the problem was with the 9 interface silver fingers on the new 1200XL Keyboard flexible Mylar was not making proper contact with the 1200XL Keyboard Hard PCB mating 9 interface fingers. To fix this Mylar Interface problem Best came up two cures. We designed (of course a brand new tooling cost to the project) a very very small wafer thin interface PCB board (two different version prototype samples made) with 9 Gold plated fingers top and bottom side of the wafer thin PCB.

 

The top and bottom Gold plated fingers on this very small interface PCB board are electronically connected together thru two plated thru holes per finger. So this small ultra thin sandwich Interface card is designed to sit between the new 1200XL Keyboard mylar 9 interface silver fingers and the larger 1200XL PCB backing board with it 9 interface fingers. As extra redundant Insurance, Best had our Keyboard manufacture triple screen 9 silver interface on the 1200XL Keyboard mylar in a effort to add extra thickness on the interface fingers on the 1200XL keyboard mylar.

[flashjazzcat]

Hmmm... Sledgehammer and nut spring to mind.

[+mytek]

I think the idea of using 'rigid' contact surfaces, no matter what the thickness is bound to fail. Probably something more like what was used in the XE keyboard connectors would be better, where you have a leaf spring contact applying constant pressure against the mylar contact surface. This stands a much better chance at maintaining electrical connectivity over an extended time period. Don't know if that idea could be applied to the 1200XL, but some kind of springy material that could be sandwiched could possibly provide a similar solution.

 

- Michael

[+bob1200xl]

Yes, spring contacts would be nice, but the Best mylar seems to work fine if you clean off the PCB contacts, and maybe the mylar contacts.

 

There is still an open question as to whether this k/b PCB itself is bad. Like a bad scanner chip...

 

Bob

 

send it to me, I'll fix it.

[electronizer]

Following BillC's suggestion, I emailed Brad. He responded right away and said at this point, I had nothing to lose by removing the remaining layers of carbon and silver from the PCB traces. So, the same advice that bob1200xl gave in the first place.

 

I used Goof Off and it worked wonderfully. There is actually a little piece of plastic tape covering the gold traces on the PCB. On one side of the tape (the side that connects to the PCB) there are carbon traces, and on the other side there are silver traces. Each trace seems to have two vias that make an electrical connection between the carbon on the bottom of the tape and the silver on the top of the tape. I have no problem with vias on a PCB but on a piece of plastic tape? I'm guessing that's why a lot of these keyboards stop working.

 

 

 

Brad had suggested to use the thin, gold plated wafer on reinstallation, but I did as bob1200xl suggested and put the keyboard back together without it. I connected everything up, turned on the computer, and it worked like a charm!

 

Mytekcontrols mentioned that the XE keyboard connectors have a leaf spring contact that applies constant pressure against the mylar contacts. The Best 1200XL mylar has a piece of double-sided foam tape directly underneath the contacts on the back side of the mylar that does essentially the same thing—pushes the contacts on the mylar against the contacts on the PCB. This was enough in my case to make a good connection, without a need for the thin wafer.

 

So, I'm very happy—glad to finally have this computer up and running again. I ran the self test to see the easter egg where the keyboard test spells out the designer's name. Pretty cool, I had never seen that before.

 

Thanks everyone for your advice! Next step is to install the second Best 1200XL mylar I bought in the garage sale 1400XL I found earlier this year.

[+DrVenkman]

Thanks everyone for your advice! Next step is to install the second Best 1200XL mylar I bought in the garage sale 1400XL I found earlier this year.

 

*record scratch*

 

Wait, what?!?! Wow! Is there a thread about that? And how come shit like that never happens to me?!?

[toddtmw]

 

*record scratch*

 

Wait, what?!?! Wow! Is there a thread about that? And how come shit like that never happens to me?!?

I KNOW!! How come I never find cool stuff at garage sales???

[towmater]

I just installed the Best mylar, and based on these suggestions I left out the thin PCB, everything seems to work fine without it.