(347) 552-2258 [email protected]

SOLVED A2338 820-0020 left shift doesn't work

D

DDVL

Member
So this machine came in with liquid damage
Had no image, ghost input and fan fast
For no image
i just replaced the resistor rr201 with a 100k and that worked
For fan fast
i replaced ue501
For ghost input
I replaced jt200 and dzt204 dzt 203( they looked damaged)

And now i am stuck as the left shift doesn't work, tried with a different keyboard as well
Plzz help
Thank you in advance
 
2informaticos

2informaticos

Administrator
Staff member
Left shift key is included in the keyboard matrix.
Only right shift, left option and control keys are independent.
Really strange issue...
 
D

DDVL

Member
I figured, i tried reading the schematic but there isn't a detailed version of the keyboard matrix for me to look at and understand.
I have already tried 2 keyboards and trackpads and now i am at my wits end. Is there anything i can look for specifically?
 
D

DDVL

Member
Is there going to be a difference from the in built keyboard viewer in macos vs an online one as i already checked with the inbuilt one
 
D

DDVL

Member
So i reinstalled the os just to be on the safe side and again still no left shift. I am at a loss. Idk what to try next.
 
2informaticos

2informaticos

Administrator
Staff member
I don't see other reason than bad keyboard for such issue.
As I said, the keyboard is organised into a matrix.
Only RIGHT shift, left option and control keys have dedicated lines.

Any other failing line will cause more than one non-working key.
Unless no other keys connected with left shift in the matrix; you should try to find if is your case.

To understand what I mean, look at the attached pictures.
Years ago, I tried to "decode" A1278 keyboard matrix.
Be aware, that one had dedicated line for left shift key!

Since T2 machines appeared, RIGHT key is needed for DFU mode.
That's the reason to allow dedicated line for this key.
Left shift is no more involved in any special combination keys; like SMC reset before.

If you get a bad M1 keyboard, open it and follow the membrane traces.
Then you can see for sure if left shift key is alone in the matrix.
If you have a keyboard fully tested with other machine, then you can confirm if the issue is caused by your MLB.
In such case, check diode mode to ground on all KBD_DRIVE/SENSE lines; one ESD diode array may be damaged.

KB1.jpgKB2.jpgKB3.jpgKB4.jpgKB5.jpg
 
D

DDVL

Member
Hey so quick update on this, still waiting for a damaged keyboard to rip apart but in the meantime i think i have found something kbd_sense_x10 has a weird diode mode reading. Its 0.800 verus a good board and open data it should he 0.600 ish. So i replaced dzt204(again) and ut102 and nothing changed. This is the only line that seems to be out of spec. Also i checked every point of ut102 and all measurements in diode mode check out. If you have any more advice that would be appreciated otherwise I'll just update here when i find something new.
 
D

DDVL

Member
So left shift is absolutely kbd_sense_x10. I had a broken trace from ut102 to pin 2 of rt140. It had corrosion i couldn't see at all. Thanks for the help.
 
2informaticos

2informaticos

Administrator
Staff member
Thanks for feedback.
Now we know for sure that Left Shift key is connected alone on the KBD_SENSE_X10 line.
 
You must log in or register to reply here.
Top