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Interesting New Behavior of left Command Key: I sure can't figure it out.

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Hello Everyone!

I have a MacBook Pro using El Capitan (the newest OS it can use).

Starting last week, the Left command key is acting odd only when combined with the Ctrl key & I'm lost.

The Right command key works fine- even with the Control (Ctrl) key. (There's only one Ctrl key)

When only Command is needed, such as Cmd-Q to quit an application, the left command key is fine.

I can not figure out why Left Command can no longer combine with Ctrl to perform a function when Right Command does combine with Ctrl just fine.


The behavior is identical in both User Profiles. P-Ram & SMC reset did not solve the problem.

Does this sound like a hardware problem with the Left Command key? (Maybe it has 2 separate contacts on the circuit board & the one that is needed for using with Ctrl is bad?)

Thanks For Your Thoughts!
Paul
 
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I can not figure out why Left Command can no longer combine with Ctrl to perform a function when Right Command does combine with Ctrl just fine.

When I did this new behavior start happening???

Have you added any utility or Applications recently???

Do you have the same "problem" when you boot using Safe Boot Mode???

Have you added any new Customized keyboard shortcuts lately, or does anything related show when you check any that are already created???

Also, I would suggest going through all the various settings of the Keyboard System Preference pane, and maybe even consider doing a reset where offered.




- Patrick
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Thanks Patrick for taking time to reply & offer insights.

Error Of Omission: I forgot one, possibly important, clue- The Function Key quit working. I don't know if it quit at the same time as this other problem, or if it quit earlier. I don't use it terribly often.

To Answer Your Quesitons-
Behavior started last week.

No new utilities, applications or even updates have been done since long before the problem started. It's been more than a month since last application update & about 6 months since last new application was installed. (Unless an application self-updates without my knowledge)

No special customizations to keyboard or Word macros.

I did search System Preferences - Keyboard a couple of times since the trouble began. I put all choices to Restore Defaults each time. No luck.

I didn't think of Safe Mode. Thanks for thinking of it. Unfortunately, the problem remains when booted safe.

What is puzzling me most is that some key combinations, such as Ctrl-Cmd-T for text in preview, work with the right Cmd key, but not the left. And, all Cmd only items work left or right, such as Cmd-Q to quit an application.

So it seems the left Cmd key does something, just not in combination with Ctrl, and the Right Cmd key does work with Ctrl.
 
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So it seems the left Cmd key does something, just not in combination with Ctrl, and the Right Cmd key does work with Ctrl.

If you want to confirm what a keypress does or doesn't do, enable the "Keyboard viewer" nd watch iy to see what happens, or not, when you press any key or combination.

The "Keyboard viewer" will show what keys are registering when pressed if they are actually working. Just a means to check keystroke connections.

Any chance any of the keys are stuck in the down position perchance???

Anything get spilt on the keyboard recently???





- Patrick
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Thank You Patrick for sticking with me on this confusing problem.

No spills & all keys bounce back up.
I took the key cap off to see if the silicone button was actually going up and down. It does.


Thanks also for your suggestion to use Keyboard Viewer. I never knew it was there. The viewer's mighty handy.

Keyboard Viewer Results:
I did all the combinations & found:
Control-Left Command only lights up the Control key. (The trouble spot)
Control-Right Command lights up both the Control & Both Command keys.

Left Command Alone lights up both Command keys
Left Command in combination with any other key- except Control- lights up all pressed keys.

Since Left Command works except when combined with Control, I am not sure if the focus should be hardware or software.

PS: Function Key does not work at all, so I believe Function is certainly a hardware problem.
 
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Thanks Patrick!

A new symptom arose today:
Command-P used to bring up the Print dialog. As of this morning, only the Right Command key + P will bring up the dialog. The Left one does not.

I studied all the preference files & didn't find one where eliminating solved the problem. (But, I don't honestly know what I am seeking, so I guessed & experimented.)

I did the PRAM & SMC resets a couple of times. No luck.

Since the Function key is most likely physically broken, I ordered a used keyboard on eBay for 8.00 USD. It can't hurt to try it out.

If the Command problem remains with the new keyboard, I'll go with your idea of a preference file being corrupt. I'll be sure my backup is good and experiment with more plist files. Hopefully, I'll find the bad guy.

Once the global health crisis is over and I'm back to working (& we're eventually caught up financially), it sounds like that will be a good time to concentrate on saving for a new MacBook Pro. New stuff is always fun!
 
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I did the PRAM & SMC resets a couple of times. No luck.

Since the Function key is most likely physically broken,

You can use the Keyboard Viewer to virw or check the operation of any key on your keyboard.

It's easily Enabled from the keyboard System Preferences pane and then accessed from the Keyboard input on the menu, if it is Enabled.

PS: Are you sure the battery is not swollen and pressing on the thin keyboard ribbon cable that passes underneath the battery on some similar MacBook models, or maybe I am thinking of some much earlier models that sometimes had the problem.




- Patrick
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It's easily Enabled from the keyboard System Preferences pane and then accessed from the Keyboard input on the menu, if it is Enabled.



- Patrick
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Patrick, check out Post #5, for what happened with Kyboard Viewer.


Sent from my iPad using Mac-Forums
 
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Sometimes I'm not the brightest bulb in the proverbial chandelier! I should have thunk of this test sooner:
My computer has 2 partitions, each with OS X 10.11.6.
I booted to the second partition and gave a fresh installation of OS X, so it would be pristine. Testing the Command key in that partition gave the same results, so I think that eliminates a preference file problem and confirms a mechanical problem.

It will be interesting when the new (used) keyboard arrives- assuming the replacement solves the problem- to take the old one apart to visually check if there is a second, failed, contact in the left Command key. (Since some command-other key functions work & some don't)

Thanks Again Patrick & Bob for mentioning Keyboard Viewer. I'm really enjoying exploring & using it.
 
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My computer has 2 partitions, each with OS X 10.11.6.

I'm going to refrain myself with difficult here and not ask the reason for doing so. :Smirk:

Maybe in order to have a pristine user OS X boot test volume...??? Just curious.
But then, why the reason to give a fresh installation of OS X???

And good luck with this unless it's something really obvious that might be broken or misplaced. I've never been able to find a reason with a broken keyboard, Even when using a jewelers loupe or strong magnifying glasses.
It will be interesting when the new (used) keyboard arrives- assuming the replacement solves the problem- to take the old one apart to visually check if there is a second, failed, contact in the left Command key. (Since some command-other key functions work & some don't)
I hope everything works out for you.






- Patrick
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I'm going to refrain myself with difficult here and not ask the reason for doing so.

The second partition's for when I get new software so that I can test drive it to make sure it doesn't wreck stuff on the "real" volume. Back when 10.11 was getting updates, I'd also do the update on the "Fallout Shelter" volume first to find glitches.

I suppose that is a left over habit from when I had a Windows machine & it's probably not necessary with a Mac OS- especially since I get a new application about once every 2 years.

The autopsy on the old keyboard will be just for doubtfully successful exploration, kind of like looking for the Holy Grail. Like you mentioned, I don't expect to find the cause.

Thanks Again Patrick. I'll post what happens with the replacement keyboard and my archeological exploration of the old one.

Enjoy Today!
Paul
 
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Thanks Again Patrick & Bob for helping me with this problem.
I had a chance to install the "new used" eight-dollar keyboard and life is good!

I did make one mistake by not sealing the upper edge of the black liner that lays on the keyboard assembly. The backlight for the keys would flash on & off in perfect one second timing. The light was leaking out and tricking the backlight sensor. Oops!

For fun, I dissected the old keyboard to try to learn why the left command key only worked with some key combinations. It turns out that there are two separate circuit traces for that key. One had lint under it. I re-assembled and tested the keyboard. Now I have a working spare.

Since I found how the keyboard works interesting, I'll make a Just For Fun post with the autopsy photos. Perhaps it will prove useful to someone in the future for diagnosis.

Thanks Again & Be Sure To Enjoy Today!
Paul
 
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It turns out that there are two separate circuit traces for that key. One had lint under it. I re-assembled and tested the keyboard. Now I have a working spare.

Congratulations on your discovery and fix.

Actually, I'm rather surprised you were able to see the lint causing the problem. Well done!!!




- Patrick
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Actually, I'm rather surprised you were able to see the lint causing the problem.


To be honest, Patrick, there was enough lint to knit a sweater, so it wasn't too hard to spot.
 
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