+slx Posted January 26, 2021 Share Posted January 26, 2021 I re-opened and re-installed the new membrane tonight and have the following observations: BREAK key works for me, all others don't I tested some keys (space, M) for continuity with an Ohm meter and found that the keys do make a contact I have tested this at the motherboard connector as well, so the connector should not be at fault pressed keys have a resistance of 12-14 Ohms I am in no way an electronics guru so please excuse if the following question makes no sense. Could it be that the 12-14 Ohm resistance is too high for the system to register and BREAK registers because IIRC it is connected through a different circuit than the other keys? 1 Quote Link to comment Share on other sites More sharing options...
RWAP Posted January 26, 2021 Author Share Posted January 26, 2021 21 minutes ago, slx said: I re-opened and re-installed the new membrane tonight and have the following observations: BREAK key works for me, all others don't I tested some keys (space, M) for continuity with an Ohm meter and found that the keys do make a contact I have tested this at the motherboard connector as well, so the connector should not be at fault pressed keys have a resistance of 12-14 Ohms I am in no way an electronics guru so please excuse if the following question makes no sense. Could it be that the 12-14 Ohm resistance is too high for the system to register and BREAK registers because IIRC it is connected through a different circuit than the other keys? Hmm - it could well be that - does anyone know what the value of the pull up resistors are for the keyboard? I can then pose the question with the factory. Quote Link to comment Share on other sites More sharing options...
+slx Posted January 26, 2021 Share Posted January 26, 2021 Encouraged by @Sugarland's example I cleaned the contacts on the original mylar with 99% alcohol and Q-tips and re-installed it with two layers of insulating tape on the plastic crossbar beneath the connector for "extra pressure" and have all keys working. Measured resistance is 11.something Ohms on the Space and M keys, seems to be not too different from the new mylar. The only (other) difference between the two is the protective foil/plastic that covers most of the contact side of the old mylar, leaving only the round connectors open. (That's the white stuff that sticks to the board when disassembling the keyboard, clearly visible in post #26.) Could it be that the open conductors/conduits between the individual key contacts make contact with something they shouldn't? I checked the Best 1200XL mylar (the only one I happened to have handy) and the conduits outside the key contacts are covered by something as well. I have attached a picture showing the difference (contact side shown up on both). As for the "extra pressure" on the keyboard, I don't think that's an issue. The keys have little springs on the bottom side that seem to limit/reduce the pressure a key can exert on the mylar. As an electrical contact is made anyway, I don't think that can be increased considerably by pushing harder. 1 Quote Link to comment Share on other sites More sharing options...
+slx Posted January 26, 2021 Share Posted January 26, 2021 To test my theory of the open conductors, one could try to cover the conduits between the key contact pads with "something", maybe some kind of lacquer. @RWAP, would this be OK for you or do you need the non-working mylars returned? Any suggestions what to use as a makeshift insulator? Maybe a layer of tape or very thin plastic with holes punched in the right places? There are tools to punch neat holes but I don't have any. Quote Link to comment Share on other sites More sharing options...
RWAP Posted January 26, 2021 Author Share Posted January 26, 2021 Happy for you to try different approaches - one thing which people successfully trialled on the Commodore SX-64 was to use a piece of insulating tape between each of the key pads. If that is required, then the factory will produce a thin plastic spacer sheet which has holes for each of the key pads and sits between the keyboard and the membrane.... At the moment, the factory are not working because of Covid restrictions. Quote Link to comment Share on other sites More sharing options...
+slx Posted January 26, 2021 Share Posted January 26, 2021 1 hour ago, RWAP said: If that is required, then the factory will produce a thin plastic spacer sheet which has holes for each of the key pads and sits between the keyboard and the membrane.... Scotch tape (sellotape) should do the trick as well and is thinner, especially the "invisible" type. I closed my 800 up for tonight but will give it a try ASAPd. Might be a week and a half until I find enough time, though, so maybe @Sugarland is faster. The Best mylar seems to have a second, punched foil applied ("glued", probably rather fused) onto the base foil with the conductors in between. The whole thing feels a bit thicker and stiffer. Are there any more prototype testers around? Quote Link to comment Share on other sites More sharing options...
Sugarland Posted January 27, 2021 Share Posted January 27, 2021 I would not recommend regular scotch tape because it does not age well and the glue will spread. I hope there are more 'prototype' testers. I'm not willing to again remove the membrane from my Mitsumi 800 because it is working 100% right now. Quote Link to comment Share on other sites More sharing options...
adam1977 Posted January 28, 2021 Share Posted January 28, 2021 I've got one of Rich's membranes in my 800, I tested it a couple of weeks ago, i've been snowed under with work since, but here's my finding's: The top row doesn't respond. The second row doesn't respond up until the 'U' key, the rest of the keys on that row are fine. The third row keys are fine to 'H', 'J' key onwards doesn't work and i'm not sure about CTRL. With the final row, only keys 'N' onwards work The space bar is fine. I think it's just down to contacts between the keyboard and mylar and over this weekend i'm going to try some foam, paper etc and see what works best Quote Link to comment Share on other sites More sharing options...
+slx Posted January 28, 2021 Share Posted January 28, 2021 Good news! I tried the ‘invisible’ Scotch tape fix, taping over all the conduits between the round key contacts and ended up with a fully working keyboard! I thought about trying roll-on correction tape which would be way easier to apply (saving a lot of snipping off little pieces of tape) but didn’t find any and don’t know if it’s insulating (but probably lasting longer than Scotch tape). When you order a punched in-between foil, don’t forget the alignment holes. If they can add a punched insulating layer fused to the Mylar, even better. As for installation, I made a few pictures and will try to cobble them together. It’s possible to swap the Mylar without detaching the keyboard ribbon and removing the keyboard base from the top shell. I certainly hope I never have to open those tiny Mitsumi screws again! If the cleaned Mylar lasts another 35 years I have a decent chance of being dead by the time it needs replacement or at least senile enough not to mind. Next up would be some Stackpole plungers for the other 800... 1 Quote Link to comment Share on other sites More sharing options...
+slx Posted January 28, 2021 Share Posted January 28, 2021 4 hours ago, adam1977 said: I think it's just down to contacts between the keyboard and mylar and over this weekend i'm going to try some foam, paper etc and see what works best Interested in your results. If it’s really the uninsulated conduits making contact where they shouldn’t, pressure (and thus more contact) should make it worse rather than better. The Break key might not be affected because its conduit runs along the edge of the Mylar and doesn’t cross any board conduits. 2 Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted January 28, 2021 Share Posted January 28, 2021 (edited) this means they forgot the separator sheet for the mylar! the old mylar had silicon that kept the traces going from pad to pad touching.. tell whomever is making these to include the thin separator sheet with the pad holes cut out for the keys! Lucky no damage happens as almost all keys were shorted together! Edited January 28, 2021 by _The Doctor__ 1 Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted January 29, 2021 Share Posted January 29, 2021 Just to add... I bought two and am having the same issues everyone else is having. I've been trying to solder the fingers on the board side to give a bit more height but that doesnt seem to be working all that well. if this "separator sheet" works that would be great news! Better yet, I hope that Krenath fellow is successful in making a full cherry replacement. I'm starting to hate this mylar stuff. 1 Quote Link to comment Share on other sites More sharing options...
Sugarland Posted January 29, 2021 Share Posted January 29, 2021 38 minutes ago, Stormbringer said: Just to add... I bought two and am having the same issues everyone else is having. I've been trying to solder the fingers on the board side to give a bit more height but that doesnt seem to be working all that well. if this "separator sheet" works that would be great news! Better yet, I hope that Krenath fellow is successful in making a full cherry replacement. I'm starting to hate this mylar stuff. It seems we can fix this issue by using a tape or something to separate the two mylar layers apart. If you ever get a cherry replacement I'll gladly buy your Mitsumi, please! Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted January 29, 2021 Share Posted January 29, 2021 I dont see this as being one issue alone but at least two. one seems to be the separator sheet and the other seems to be the mylar doesn't contact the fingers on the board with even pressure. is there a conductive glue? these might have to be carefully adhered with those having the second issue. Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted January 29, 2021 Share Posted January 29, 2021 @RWAP do you see what is needed, a separator sheet with contact holes that insulates the traces between pads... and a pressure increasing shim for contact fingers... easy peasy cheap as can be fix 1 Quote Link to comment Share on other sites More sharing options...
RWAP Posted January 29, 2021 Author Share Posted January 29, 2021 Great - thanks for the experimentation - do we have any ideas as to how thick the little bit of foam needs to be on the back of the fingers? Quote Link to comment Share on other sites More sharing options...
+slx Posted January 29, 2021 Share Posted January 29, 2021 2 hours ago, Stormbringer said: Just to add... I bought two and am having the same issues everyone else is having. I've been trying to solder the fingers on the board side to give a bit more height but that doesnt seem to be working all that well. if this "separator sheet" works that would be great news! Better yet, I hope that Krenath fellow is successful in making a full cherry replacement. I'm starting to hate this mylar stuff. If you have a tool to punch holes like the one below you could put a thin sheet of paper or plastic over the mylar, cut out the contact strip, mark the location of the contact pads and punch holes, then install that sheet between the mylar and the circuit board. I used used Scotch "magic tape" but Sugarland is probably right to say that's not a long-term solution. It worked for testing if the missing insulation was at fault, but took about half an hour of snipping little bits of tape and prying them off the scissors as normal tape is wider than the distance between two key contact pads. The keyboard has a nice feel and with new replacement mylars I'm confident it will outlive me. Now, if somebody would mass produce new plungers for 800 Stackpole keyboards... Quote Link to comment Share on other sites More sharing options...
+slx Posted January 29, 2021 Share Posted January 29, 2021 9 minutes ago, RWAP said: Great - thanks for the experimentation - do we have any ideas as to how thick the little bit of foam needs to be on the back of the fingers? I should think that something very thin (<1mm) would be sufficient. Two layers of insulating tape did the trick for me and that's well below 1mm. Be sure to remove any gunk from the board's contact fingers. (For both @Sugarland and myself it was actually sufficient to clean the contacts plus those on the old mylar to get it working again (Q-tips and 99% alcohol for me). Quote Link to comment Share on other sites More sharing options...
spookt Posted January 30, 2021 Share Posted January 30, 2021 I’ve got a couple of these replacement molars waiting to be installed. Is it better to hold of for and official fix? I didn’t realise there were issues until now. Quote Link to comment Share on other sites More sharing options...
Sugarland Posted January 30, 2021 Share Posted January 30, 2021 17 minutes ago, spookt said: I’ve got a couple of these replacement molars waiting to be installed. Is it better to hold of for and official fix? I didn’t realise there were issues until now. Does your 800 mitsumi work right now? If it's working 100% now then I'd say wait. Quote Link to comment Share on other sites More sharing options...
RWAP Posted January 30, 2021 Author Share Posted January 30, 2021 Yes I would advise waiting. We have had this before where the factory try the membranes on a test machine without any issues, but once they reach the hands of the actual users, it is a different story. Once the factory is operating normally, I will get a plsastic spacer made and something to put extra pressure on the back of the fingers to ensure better contact and send these out. Rich 3 Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted January 30, 2021 Share Posted January 30, 2021 and the trace isolation and pad hole sheet.. 2 Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted February 8, 2021 Share Posted February 8, 2021 On 1/30/2021 at 3:13 AM, RWAP said: Yes I would advise waiting. We have had this before where the factory try the membranes on a test machine without any issues, but once they reach the hands of the actual users, it is a different story. Once the factory is operating normally, I will get a plsastic spacer made and something to put extra pressure on the back of the fingers to ensure better contact and send these out. Rich If you dont mind me asking, what kind of time-frame do you think that would be? Quote Link to comment Share on other sites More sharing options...
RWAP Posted February 8, 2021 Author Share Posted February 8, 2021 29 minutes ago, Stormbringer said: If you dont mind me asking, what kind of time-frame do you think that would be? No idea at the moment - it will probably be April - the factory is actually operating but just 1 person on the shop floor, worknig 3 days a week because of space. They normally have 3 people working 5 days a week! Quote Link to comment Share on other sites More sharing options...
umpledord Posted February 15, 2021 Share Posted February 15, 2021 Little late but..... Just bought an 800 and it has a bad membrane. Will there be any more released on sell my retro? If not does anybody that bought extras want to part with one? Gord. Quote Link to comment Share on other sites More sharing options...
Like us on Facebook
Follow us on Twitter
AtariAge on Instagram
Watch us on YouTube
Chat on Discord
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.