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Jurai29

XE & XL keyboard troubles

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Hi all,

 

I've been getting my 8bits back in operation and run into some troubles with keyboards. I first dug out my 130XE and hooked it up, both 1050's work fine but the keyboard was getting flakey some keys weren't working like 1, 2, Q and some others that were not grouped together. I replaced the mylar with one I got from best and it improved marginally, more keys are working except HELP, SELECT, START, OPTION aren't working so well, SELECT & OPTION being the worst off. Suddenly this week a 65XE I found at a flea market started doing the same thing, at the exact same time! well I tried cleaning the contacts where the mylars connect to the mainboard on the 65XE and the 600XL with no difference. I've spent hours on the 130XE with the new keyboard mylar also with no luck there. The new mylar is not scratched up and has no damage to the traces, that for one seems like a mystery. I can't think of any logical reason for it not to work. Btw, I have tried connecting some of the pins on the keyboard connector with a short while (after following which connected together for certain keys) and I did determine the computer itself (130XE as its my main 8bit) so I know the problem is in the keyboard itself. Is there any advice from the hardware people here I might try?

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The mylar on some keyboards simply have to high resistance thru the traces, there is a bank of resistors above j8 attached to the keyboard connector, you can use 'slightly' lower value resistors in this bank and your 130XE will not be troubled by this again. I can't believe the number of wasted keyboards and mylars that have occurred over the years as this fix was implemented and published in the user group bbs forums shortly after the XE line was introduced. dirt cheap and works forever.

Hi all,

 

I've been getting my 8bits back in operation and run into some troubles with keyboards. I first dug out my 130XE and hooked it up, both 1050's work fine but the keyboard was getting flakey some keys weren't working like 1, 2, Q and some others that were not grouped together. I replaced the mylar with one I got from best and it improved marginally, more keys are working except HELP, SELECT, START, OPTION aren't working so well, SELECT & OPTION being the worst off. Suddenly this week a 65XE I found at a flea market started doing the same thing, at the exact same time! well I tried cleaning the contacts where the mylars connect to the mainboard on the 65XE and the 600XL with no difference. I've spent hours on the 130XE with the new keyboard mylar also with no luck there. The new mylar is not scratched up and has no damage to the traces, that for one seems like a mystery. I can't think of any logical reason for it not to work. Btw, I have tried connecting some of the pins on the keyboard connector with a short while (after following which connected together for certain keys) and I did determine the computer itself (130XE as its my main 8bit) so I know the problem is in the keyboard itself. Is there any advice from the hardware people here I might try?

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The mylar on some keyboards simply have to high resistance thru the traces, there is a bank of resistors above j8 attached to the keyboard connector, you can use 'slightly' lower value resistors in this bank and your 130XE will not be troubled by this again. I can't believe the number of wasted keyboards and mylars that have occurred over the years as this fix was implemented and published in the user group bbs forums shortly after the XE line was introduced. dirt cheap and works forever.

I remember doing this mod (or one like it) to my first 130XE back in the 80's but I have not seen it anywhere recently. Does anyone know where it might be documented?

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The mylar on some keyboards simply have to high resistance thru the traces, there is a bank of resistors above j8 attached to the keyboard connector, you can use 'slightly' lower value resistors in this bank and your 130XE will not be troubled by this again. I can't believe the number of wasted keyboards and mylars that have occurred over the years as this fix was implemented and published in the user group bbs forums shortly after the XE line was introduced. dirt cheap and works forever.
Hi all,

 

I've been getting my 8bits back in operation and run into some troubles with keyboards. I first dug out my 130XE and hooked it up, both 1050's work fine but the keyboard was getting flakey some keys weren't working like 1, 2, Q and some others that were not grouped together. I replaced the mylar with one I got from best and it improved marginally, more keys are working except HELP, SELECT, START, OPTION aren't working so well, SELECT & OPTION being the worst off. Suddenly this week a 65XE I found at a flea market started doing the same thing, at the exact same time! well I tried cleaning the contacts where the mylars connect to the mainboard on the 65XE and the 600XL with no difference. I've spent hours on the 130XE with the new keyboard mylar also with no luck there. The new mylar is not scratched up and has no damage to the traces, that for one seems like a mystery. I can't think of any logical reason for it not to work. Btw, I have tried connecting some of the pins on the keyboard connector with a short while (after following which connected together for certain keys) and I did determine the computer itself (130XE as its my main 8bit) so I know the problem is in the keyboard itself. Is there any advice from the hardware people here I might try?

 

I never heard that before either. I suppose you can just add lower resistance resistors on top of the existing ones (where needed) so you don't have to desolder.

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I all use to reside on the Parallel Dimension, Starship, Starfleet, ACUTE, and closer to home, and CSS BBS's.

Now it is only coming from what is left of my memory. I use to Doctor quite a few eight bits for free back in the days of plenty, it kept us very busy. I recently had contact with GTO 'The Tyrant' about the old boards, he has assured me some of it is still in boxes but his life is about the kids, wife, job, and cars now. My3.5 inch backups failed. The full height seacrate ate itself.....

 

The resistor value if you piggy back/parallel them needs to be somewhat high to prevent taking the resistance to low. Only take it as low as it needs to function. I used a decade resistance box to custom tailor each one. But a one size fits almost all value was in the dox at the time. I simply do not recall the value and apologize for my failing grey matter.

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I recently repaired/reconditioned a 1200 XL keyboard (this very one in fact). I peeled back the mylar and cleaned the contacts (both sides) with rubbing alcohol and q-tips. Initially it had only two keys working, and now everything works!

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Hi all,

 

What's purturbed me is what keys and how many affected seems to be very intermittent, mostly is the "function" key row aka Select, Start, Option etc. Anyone know what resistor values to substitute? I have a small stockpile of parts so coming up with resistors shouldn't be much trouble. Piggybacking does involve some calculating as resistors in parallel are always lower. I had the same thought Jacobus did and had tried the alcohol cleanup tip already which unfortunately didn't help even on the 600XL I have where the traces had gotten badly corroded. It does bother me as it again delays me getting my 8bit fix.

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This is for the XE computers.

It is best not to rub the mylar's traces, that oxidation protects what is left of the traces, if you clean them all it exposes fresh

materials to oxidize causing the whole thing to repeat. As was evidenced, new old stock mylar did not correct the problem.

 

The amount of resistance to decrease in this case looks to be quite minimal as the keys are at the borderline.

 

A target combination equal to 220 ohm should be safe.

Do not disturb the 47k resistor (yellowvioletorange) or the diode above it.

 

1.2k ohm (brownredorange) in parallel with the existing 270 ohm resistor should get you down to 220 ohms.

1.1k and you get 216. You can nudge it down to 1k and get 212 and so on. only use what gets the job done...

 

if you cleaned the mylar off go one step below what first gets the keyboard working, that will ensure that it keeps working

after the next round of oxidation is complete.

 

There you have it.

 

some formulas for calculating resistance in parallel are

Combined resistance of two resistors in parallel:
  	R=[u]R1×R2[/u]
         R1+R2
For more than two resistors connected in parallel a more difficult equation must be used.
Add up the reciprocal(one-over) of each resistance to give the reciprocal of the combined resistance
Rtotal:[u]
[/u] [u]1[/u] = 	 [u]1 + 1 + 1 + [/u]...
R 	 R1  R2  R3  ...
The simpler equation for two resistors in parallel is much easier to use! 

Edited by _The Doctor__

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1.2k should have been brown red red

This is for the XE computers.

It is best not to rub the mylar's traces, that oxidation protects what is left of the traces, if you clean them all it exposes fresh

materials to oxidize causing the whole thing to repeat. As was evidenced, new old stock mylar did not correct the problem.

 

The amount of resistance to decrease in this case looks to be quite minimal as the keys are at the borderline.

 

A target combination equal to 220 ohm should be safe.

Do not disturb the 47k resistor (yellowvioletorange) or the diode above it.

 

1.2k ohm (brownredred) in parallel with the existing 270 ohm resistor should get you down to 220 ohms.

1.1k and you get 216. You can nudge it down to 1k and get 212 and so on. only use what gets the job done...

 

if you cleaned the mylar off go one step below what first gets the keyboard working, that will ensure that it keeps working

after the next round of oxidation is complete.

 

There you have it.

 

some formulas for calculating resistance in parallel are

Combined resistance of two resistors in parallel:
  	R=[u]R1×R2[/u]
         R1+R2
For more than two resistors connected in parallel a more difficult equation must be used.
Add up the reciprocal(one-over) of each resistance to give the reciprocal of the combined resistance
Rtotal:[u]
[/u] [u]1[/u] = 	 [u]1 + 1 + 1 + [/u]...
R 	 R1  R2  R3  ...
The simpler equation for two resistors in parallel is much easier to use! 

Edited by _The Doctor__

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Hey @_The Doctor__, I was working on cleaning up a 130XE this past week that was previously upgraded to 320K BITD, and I came upon this area of the PCB. These 'piggybacked' resistors sure look like the keyboard mod you describe above. Any idea which keys these three resistors here would be helping? I'm guessing start/select/option, as the reset key seems ever so slightly less responsive...

 

 

keyboardresistors.jpg

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YES, looks like a variation on it... and the start select and option keys are often the ones people fix first. I see they tried to solder up the header as well  (lots of solder under there) looks possibly damaged on the right hand side also.

 

make sure that first right hand side contact is on the correct side of the Mylar when re-inserting the ribbon if possible.

the next three contacts go to the traces that connect to those resistors.

 

so the muffed pin is reset pin (24)

the three before the muffed pin are s0 (21) s1 (22) s2 (23)  (that is START/SELECT/ and OPTION) resistors 134,135,136

 

so you have found the fixes in the wild....

adding a picture of where the wire is attached would be a nice touch

 

amazed @Nezgar found my ancient post when I actually knew what I was up to! :) and am glad that helped some people out over the years...

Edited by _The Doctor__
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Oh yeah I forgot to mention about that connector. the far right pin of the connector looks like it got pushed down too far, so the previous owner inserted a small piece of wire to help improve contact again I guess. Yes, I ensured it was on the contact side of the mylar connector when I reinserted. It's a tight fit, but it works, so I'm not too worried about it at this point... The bottomside of the PCB where the keyboard pinch connector is has a lot of flux residue so it was definitely topped up, or replaced entirely at some point.

 

Sure wish there was a source of that 24-pin pinch connector someplace. I was looking at digikey's site, and I hold hope that there could be a part, but without pictures its pretty tough.

 

39 minutes ago, _The Doctor__ said:

picture of where the wire is attach would be a nice touch

Here you go.

keyboard.thumb.jpg.5f615951f292fd8de37744154ac3f88e.jpg

Edited by Nezgar
Added photo showing where the wire is attached.

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believe it or not someone listed where and what it is to get the replacement somewhere on the forum... unless I dreamed it... ;)

 

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There is a mylar in the keyboard, which has a matrix for a key contact fields connected by a traces. That traces increases resistance over time (after years) by oxydizing. Especially traces which has higher current, oxydize quicker. Start-Select-Option line shares ground with power LED, so there it higher current all the time. This is a reason why these keys stops working first. When you press Start/Select/Option key, then you give a GND for GTIA proper pin, but if the resistance of trace on mylar is to high, then GTIA has not enought GND signal and don't see the key is pressed.
To fix such problem we need to decrease resistance to the GND. So you can do that by several ways. The simplest and probably the best is a new mylar. Another is paint over traces by some conducting varnish.
On your photos someone solders that three resistors between Start/Select/Option lines and GND. This resistors are connected paralely to the keys, so the resistance between GND and key press is smaller, so it probably fixes the problem temporarily. The value of resistors must be experimentally chosen as smaller as possible, but high enough to prevent reading key press without key pressed. I think that is imposible if trace resistance is to high, so I think it's temporary solution for short time.

Edited by Mq.
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in the case of most of the ones I did such modifications to, it's been 23 years give or take so being that it's temporary then I'm very happy..

I prefer to keep resistance in the circuit to keep from oxidizing the traces much more so If you are going to use @Simius trigger fix I'd consider adding some resistors... (??110?ohm?+/-??) give or take I haven't measured what the trigger resistance is but it can't be much...

 Posted on it a few times & made some mix ups but it's enough to sort it... (s0s1s2) nearly every time so I needed to post all the same again clearly outlining keys from console...

here's a decade project kit for you.... however these can be had even more cheaply, it will get the job done....I couldn't imagine being without one back in the day....

https://www.sparkfun.com/products/13006

 

but you can also use a meter and do the math ;)                   @Nezgar what colors are added resistors bands? measure?

Edited by _The Doctor__
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Oh, I didn't know it:-) I see this mod for first time, so I interpret it on the fly:-) It's good to hear it's good mod. _The Doctor__ can you tell me what value of resistors you use for such mod?

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5 hours ago, _The Doctor__ said:

what colors are added resistors bands? measure?

Yeah I should have measured, but I've already closed up the machine. Looking at these pics the added resistors appear to be:

 

Orange/White/Red/Gold = 3.9k Ohms 5%

 

Checking the silkscreen in the 130XE Reference Manual, they're over R134/135/136. The parts list description for those are:

 

Res: 220 Ohm 1/4W 5% Carbon

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I never trust photos unless I verify that it looks like it should first hand as in natural light... I couldn't tell because it looks different in one photo vs the other... but it sounds right....  just want to sure and see what ends up being used out there.

 

https://atariage.com/forums/topic/142703-xe-xl-keyboard-troubles/?do=findComment&comment=4354555

 

Edited by _The Doctor__

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Well, it turns out this topic was a timely discovery / discussion. My next 130XE on the cleanup list suffered from this exact problem with the function keys. All three of Start/Select/Option were non-responsive. Every other key on the keyboard worked perfectly, and visual inspection of the mylar showed it still in great condition.

 

Last night I checked the resistance on R134,R135,R136, and even though the computer was not registering the keypresses, I could see changes in the values on the multimeter when pressing the keys, which confirmed the keys were "alive":

Start: Not pressed=2300Ω Pressed=1300Ω

Select: Not pressed=2380Ω Pressed=1280Ω

Option: Not pressed=2370Ω Pressed=1240Ω

 

So tonight onto the next step. Initially I went straight to adding a 4.7KΩ resistor, and it didn't work... then moved onto installing a potentiometer to get measurements, then realized I had chosen a bad ground source the first time around... Anyway, key presses started intermittently registering with the pot "in parallel" at about 8500Ω, and started intermittently ALWAYS registering (even without a keypress) at about 1700Ω. This confirmed to me that 4.7KΩ should be a good choice, being kind of in the middle of those two values. (the 3.3K resistors seen in the previous machine also make sense in this range)

 

So I put together a triple resistor thingamajiggy, and used an open ground point via closer than that seen used by the last machine, which looks quite nice if I do say so myself. :D Now this keyboard's function keys now work!

 

130XE_kbd_resistors1.thumb.jpg.73fe9b501d01e9aaf64146a5c3937d0a.jpg 130XE_kbd_resistors2.thumb.jpg.aaf96d585f802ead9294abc62ad34ecb.jpg

 

Thanks @_The Doctor__ for the additional previous topic links too. I am intrigued by @Simius's post about using transistors instead, but I'd like to see an installed photo, schematic diagrams are hard for me to follow.

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4 hours ago, Nezgar said:

So I put together a triple resistor thingamajiggy, and used an open ground point via closer than that seen used by the last machine, which looks quite nice if I do say so myself. :D Now this keyboard's function keys now work!

 

 130XE_kbd_resistors2.thumb.jpg.aaf96d585f802ead9294abc62ad34ecb.jpg

 

Thanks @_The Doctor__ for the additional previous topic links too. I am intrigued by @Simius's post about using transistors instead, but I'd like to see an installed photo, schematic diagrams are hard for me to follow.

Clean install!  Very nice work.

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