IBM Model M keyboard acting like ALT key is always pressed

itpaul

Honorable
Nov 4, 2013
2
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10,510
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Just got an '89 IBM Model M, but the problem is that it acts like the ALT key is always pressed. I have tested this with directly plugging it in via ps2 port and using a ps2 to usb adapter from clickykeyboards.com and it acts the same either way. Both ALT keys work normally, so they don't appear to be physically stuck...

Any ideas on what's going on?

Not sure if it's circuit board related or physical key related...
 

ssddx

Titan
Moderator
is windows stickykeys turned on ?

please explain by "working normally". you say they act like they are stuck (always on) yet they seem to work. are you referring to when you hold them down they shut off?

its pretty easy to tell if the key is stuck (it either is stuck in the down position or it wont click). you could try popping the keycap and keystem off and making sure nothing is out of the ordinary. dont worry they just pull right off. you should see the spring and the little lever foot should be free moving.

with the old ibm m keyboards the biggest issue is making sure you have an undamaged membrane. sometimes they get scratches where it loops back to connect to the circuit board but this causes dead keys not a stuck key. i've had two, one with an issue (scratches that i fixed with a pencil) and another one with no issues. both worked fine via ps2 with no need of an adapter.

try a system restart as well. unplugging and plugging back in keyboards without restarting normally doesnt bode well... and sometimes they act strange.
 

ssddx

Titan
Moderator
is windows stickykeys turned on ?

please explain by "working normally". you say they act like they are stuck (always on) yet they seem to work. are you referring to when you hold them down they shut off?

its pretty easy to tell if the key is stuck (it either is stuck in the down position or it wont click). you could try popping the keycap and keystem off and making sure nothing is out of the ordinary. dont worry they just pull right off. you should see the spring and the little lever foot should be free moving.

with the old ibm m keyboards the biggest issue is making sure you have an undamaged membrane. sometimes they get scratches where it loops back to connect to the circuit board but this causes dead keys not a stuck key. i've had two, one with an issue (scratches that i fixed with a pencil) and another one with no issues. both worked fine via ps2 with no need of an adapter.

try a system restart as well. unplugging and plugging back in keyboards without restarting normally doesnt bode well... and sometimes they act strange.
 

itpaul

Honorable
Nov 4, 2013
2
0
10,510
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Thanks again for the help! It appears that issue isn't happening anymore. Something that is happening now though is when I use the left alt key and single apostrophe is usually entered as well and when I use the right alt key a forward slash is sometimes entered. Any ideas on what's going on and how I can fix it?

Thanks!
 

ssddx

Titan
Moderator
now that doesnt sound so good.

perhaps there is something wrong with the keymatrix.. eg, scratches or something on the surface causing two of the contacts to be touching.

you can take apart the keyboard to look... if its on the ribbon cable part you should be able to spot it and or fix it. if its actually on the keymatrix... you are sol.

before i'd go do that check it out on another pc to verify its not your machine first.

---

where did you buy it and what did you pay? if you dont have much invested you could always get a brand new unicomp customizer (95% like the original m).
 

Kilogeek

Honorable
Dec 5, 2013
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10,510
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I'm sorry to tell you that, but my model m died the same way... the films inside the plastic-rivets part are either geting too aged, or there may be condensated water or rust between films. I fully disassembled this part so believe me, it's not waterproof at all.
!!!!! Don't disassemble it, or do it only if you are ready to spend more than 20 hours for reassembly and you have all tools + 60 2mm nuts and bolts... you can succeed or... you can kill your keyboard for ever like I did :/
My advice would be to follow this : http://www.apartmenttherapy.com/how-to-dry-out-and-hopefully-s-107945
A rubbing alcohol bath (let soak the part for 1 to 3 hours) and let this part in a dry & hot room, but laying vertically, as if numeric keypad was bottom and tab key on top, for at least 3 days, it may fully clean and pull water out the films w/o destroying the part.
Tell us if it worked, good luck.
 

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