Author Topic: KBD75, space bar stopped working intermittently  (Read 1343 times)

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Offline Sharptsa

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KBD75, space bar stopped working intermittently
« on: Sun, 10 January 2021, 00:28:08 »
Hi,

After an unfortunate water spillage, the space bar on my KBD75(ver2) stopped working intermittently. Like it's fine for 30 minutes then it stops working for 45 minutes then comes back on.
It does not seem to be the switch because bridging the pins on PCB gives the same result.

Looking closely at the PCB, one of the diode solder seems to be a bit corroded. Could it be the cause? And would replacing it have a chance to bring it back?
Any way to test this theory without replacing it?



The diode that looks corroded to me is the R82.

Additional question : What are the diodes labelled "Spare resand Diode" on the PCB ? Are they actual spare diodes I can use?

Thanks in advance for your help!

Online LightningXI

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Re: KBD75, space bar stopped working intermittently
« Reply #1 on: Sun, 10 January 2021, 00:39:29 »
Hi,

After an unfortunate water spillage, the space bar on my KBD75(ver2) stopped working intermittently. Like it's fine for 30 minutes then it stops working for 45 minutes then comes back on.
It does not seem to be the switch because bridging the pins on PCB gives the same result.

Looking closely at the PCB, one of the diode solder seems to be a bit corroded. Could it be the cause? And would replacing it have a chance to bring it back?
Any way to test this theory without replacing it?

Show Image
Show Image
Show Image


The diode that looks corroded to me is the R82.

Additional question : What are the diodes labelled "Spare resand Diode" on the PCB ? Are they actual spare diodes I can use?

Thanks in advance for your help!


You can try reflowing the diode joint by using your soldering iron and touch it briefly.

And yes, those are "Spare Res(istors) and Diode(s)". So you can take them off with an iron and move them to the spot you need them.


Offline suicidal_orange

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Re: KBD75, space bar stopped working intermittently
« Reply #2 on: Sun, 10 January 2021, 12:52:26 »
R82 is a Resistor (that's why it's labelled R), the Diodes are Dxx.  The resistors near each switch are only used for in-switch backlighting which you aren't using so if it is corroded it wont be causing the problem.

Do the other keys in the bottom row work reliably?
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Offline Sharptsa

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Re: KBD75, space bar stopped working intermittently
« Reply #3 on: Sun, 10 January 2021, 13:44:01 »

You can try reflowing the diode joint by using your soldering iron and touch it briefly.

And yes, those are "Spare Res(istors) and Diode(s)". So you can take them off with an iron and move them to the spot you need them.

I just tried that an no change.

R82 is a Resistor (that's why it's labelled R), the Diodes are Dxx.  The resistors near each switch are only used for in-switch backlighting which you aren't using so if it is corroded it wont be causing the problem.

Do the other keys in the bottom row work reliably?

Ah ok. Yes, all the other keys are working flawlessly. Anything else I can try ?

Offline suicidal_orange

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Re: KBD75, space bar stopped working intermittently
« Reply #4 on: Sun, 10 January 2021, 14:02:36 »
If it's just the one switch/position not working and you're sure it's not the switch (it doesn't work with a wire either) then it sounds like D81 is the problem.  You can test by shorting the right hand switch pin to the top of D81 when it's not working - if it works replace D81 with one of the spares.  I have never heard of a temperamental diode but there's a first time for everything!

Alternately if the Space2 position works reliably you could remove D81 and solder a wire from the left switch pin to the bottom of D82 to effectively move the switch to the other position.  You will probably need to tweak the firmware if you do this.
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Offline Sharptsa

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Re: KBD75, space bar stopped working intermittently
« Reply #5 on: Sun, 10 January 2021, 18:24:54 »
Thank you for your help!

I did some testing :
  • space1 and space2 both work fine (when shorting)
  • shorting the right hand pin to the top or bottom of D81 does NOT work
  • shorting the right hand pin to D80 or D82 works
  • connecting the left hand pin to the one of space1 or space2 and pressing the switch works (so the switch is definitely fine)
  • connecting the left hand pin to the top of D81 and pressing the switch does NOT work
After this, my understanding is that D81 is not faulty, but the connection between D81 and the controller is. Correct me if I'm wrong, my knowledge in electronics is limited.

So the best thing to do is to solder a wire between the left switch pin to either space1 or space2. Or one of the diodes? (The diode is after the left pin right?)
Did I get it right?

At least, now I know I can fix it without having to buy a new PCB and desolder/resolder every switch! \0/
« Last Edit: Mon, 11 January 2021, 10:03:31 by Sharptsa »

Offline suicidal_orange

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Re: KBD75, space bar stopped working intermittently
« Reply #6 on: Mon, 11 January 2021, 06:33:20 »
A temperamental trace?  That's strange too but we'll go with it.

Try shorting the right pin to D65, D66 or D67 in the row above, one of them should type space.  Then short the top of D81 to the diode above and press the switch - this confirms D81 works and is connected to the switch.  If that doesn't work short the bottom of D81 and press it, if that works D81 is dead.  If it still doesn't work D81 isn't connected to the switch (and may or may not be dead)
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Offline Sharptsa

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Re: KBD75, space bar stopped working intermittently
« Reply #7 on: Mon, 11 January 2021, 10:13:57 »
Ok, so it was hard to test today as it was very temperamental. Wouldn't work at all yesterday but today it kept going on and off every 2 minutes until it was finally gone for a while.

So :
- D66 is the diode to short with the right pin to type space
- Shorting the top OR the bottom of D81 with D66 and pressing the switch works
- I also tried shorting top and bottom of D81 together and it does NOT work

Offline suicidal_orange

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Re: KBD75, space bar stopped working intermittently
« Reply #8 on: Mon, 11 January 2021, 10:49:14 »
So the easiest fix is to solder a wire between the top of D81 and the top of D66 - this is where the trace on the board runs so no side effects and nothing to remember if you ever want to change the layout.

It's still very strange to have a trace that only works when it wants...
« Last Edit: Mon, 11 January 2021, 11:35:19 by suicidal_orange »
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Offline Sharptsa

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Re: KBD75, space bar stopped working intermittently
« Reply #9 on: Mon, 11 January 2021, 11:25:38 »
Alright, thank you very much!

Just have to wait tomorrow for some wire to be delivered and I'll do the solder.

I can believe you that it's very strange. One would think that something like electronics is mostly binary working. On or off. ^^

I'll keep you updated once that's done.

Offline Sharptsa

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Re: KBD75, space bar stopped working intermittently
« Reply #10 on: Tue, 12 January 2021, 12:13:55 »
Ok, I have one last issue.

I soldered a wire between the top of D81 and the top of D66. I tested it and the space bar worked but it was chattering with double presses.
I unsoldered one end of the wire and noticed the spacebar was working (without chatter).
When connecting the unsoldered end again, the chatter is back.

Is it because when the trace works, the signal goes through the wire and trace at the same time and registers twice? If so, is there a way I can suppress it or an alternative solder I can do?
« Last Edit: Tue, 12 January 2021, 12:16:51 by Sharptsa »

Offline suicidal_orange

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Re: KBD75, space bar stopped working intermittently
« Reply #11 on: Tue, 12 January 2021, 14:22:03 »
Did you buy this board from a witchdoctor?   Seriously though, that's not right - the signal will travel down the same trace from the top diode to the controller so it can't register twice.

Do Space, Space1 and Space2 all type a space with your current firmware?  If so D66 might be typing a space but for one of the other positions.  If three diodes in the ZXCV row type a space when shorted to the right pin of your real space bar you need to solder to the middle one...
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Offline Sharptsa

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Re: KBD75, space bar stopped working intermittently
« Reply #12 on: Tue, 12 January 2021, 18:19:39 »
No, directly from KBDFans! ;D

But you are right! All three spaces are mapped in my firmware and D66 was actually the diode linked to space1. The diode for central space was D68 (and D70 for space2). I soldered the wire between D66 and D81 and everything works fine now.

I did a terrible soldering job... (I wish I had 3 hands) but it fixed the problem.
I can finally put my old crappy keyboard away. I missed the feeling of my lubed ZilentV2.  :D

Thank you again for your help and patience! You saved my board!  :thumb:
I'm not sure I would have had the courage to desolder and resolder everything on a new PCB.
« Last Edit: Tue, 12 January 2021, 18:29:58 by Sharptsa »

Offline suicidal_orange

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Re: KBD75, space bar stopped working intermittently
« Reply #13 on: Wed, 13 January 2021, 11:41:19 »
A third hand would be very useful for soldering, I agree!

Glad you got it working and sorry for not thinking about split spacebar earlier - you're the first person I've seen who broke one though you surely wont be the last.

Hopefully your case isn't see through so you can forget about the fix :)
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