Author Topic: Noticed something strange while repairing keyboard  (Read 1041 times)

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Offline ZedRedLed

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Noticed something strange while repairing keyboard
« on: April 02, 2018, 04:03:01 pm »
Hi,

I recently posted on here about a keyboard I was trying to repair. Some of the keys were connected to each other after a spillage.
Today I was looking for the cause of this, when I noticed something I don't really understand.

When I connect the membrane trace that is causing problems to one end of a wire with a ferrite bead that is connected to a capacitor near the LEDs on one side and to the membrane and microcontroller on the other, It works absolutely perfectly for about 5 minutes.
After that it goes back to keys being connected or one key being pressed infinetely (always the same key)

What could be causing this? I'm thinking perhaps a bad capacitor, but I don't know how plausible this is.


P.S.: I circled the ferrite bead in the picture of the circuit, I connect the trace with the bottom pin for the 'reset'
« Last Edit: April 02, 2018, 04:04:46 pm by ZedRedLed »
 

Offline BurningTantalum

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Re: Noticed something strange while repairing keyboard
« Reply #1 on: April 03, 2018, 08:42:54 am »
What keyboard is it?
It looks like one of the Logitech K series, maybe K800.
 
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Online coromonadalix

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Re: Noticed something strange while repairing keyboard
« Reply #2 on: April 04, 2018, 12:46:33 am »
thoses are jumper wires between 2 traces, if they have some ferrite around them, its for noise killing,  supply noise, or keyboard scanning etc ...

it goes to the white sticker microcontroller, seems to be programmable ???
« Last Edit: April 04, 2018, 12:48:11 am by coromonadalix »
 
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Offline ZedRedLed

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Re: Noticed something strange while repairing keyboard
« Reply #3 on: April 04, 2018, 08:10:10 am »
Quote
What keyboard is it?

It's a Madcatz V7
« Last Edit: April 04, 2018, 08:14:21 am by ZedRedLed »
 

Offline ZedRedLed

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Re: Noticed something strange while repairing keyboard
« Reply #4 on: April 04, 2018, 08:13:05 am »
Quote
it goes to the white sticker microcontroller, seems to be programmable

Yeah, I'm even wondering if the problem could somehow be software related, although I kinda doubt it.
I wonder what would happen if I permanently connect the trace with this jumper, although a "proper" fix would be better
 

Offline ZedRedLed

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Re: Noticed something strange while repairing keyboard
« Reply #5 on: April 04, 2018, 08:19:29 am »
Here are some pictures from the other side of the same PCB. There was some damage at the circled ferrite bead and at the capacitor (to the right, next to the 6 pin connector on the original picture)
 

Offline Rasz

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Re: Noticed something strange while repairing keyboard
« Reply #6 on: April 04, 2018, 04:55:47 pm »
sooo, it never occurred to you to clean it up?
buy new keyboard :)
Who logs in to gdm? Not I, said the duck.
My fireplace is on fire, but in all the wrong places.
 

Offline ZedRedLed

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Re: Noticed something strange while repairing keyboard
« Reply #7 on: April 04, 2018, 08:23:05 pm »
Cleaning it up was the first thing I did, the pictures are old and meant to give an idea of the damage.
I also have enough keyboards, I just want to fix this one
 

Online coromonadalix

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Re: Noticed something strange while repairing keyboard
« Reply #8 on: April 04, 2018, 09:59:33 pm »
its definitely an noise cancelling filtering ferrite,  if the jumper is good and cleaned  the keyboard still should work ??  unless some unknow damage occured while powered,  fried cpu   etc ...
 


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