CM Quickfire TK repair advice

[myotherteeshirt]

Hi guys,

I recently purchased a CM quickfire TK secondhand - almost everything is woring fine, except that the right enter key does not work *at all*, regardless whether num lock is on or off.

Anyway, i was intending to open it up anyway as my first DIY switch changing project, so can anyone give some advice on what i should be looking for if i were to try to fix the key?

[user 18]

Before you take a soldering iron to it, try shorting the pads on the PCB to see if you can get the key to register that way. If you can't, that would be indicative of a damaged trace, which is a more difficult repair process than swapping out a damaged switch.

[BrewCaps]

Why not complain to the seller and get your money back?

[myotherteeshirt]

Before you take a soldering iron to it, try shorting the pads on the PCB to see if you can get the key to register that way. If you can't, that would be indicative of a damaged trace, which is a more difficult repair process than swapping out a damaged switch.

When you say shorting the pads, i assume you mean use a copper wire (or similar) to connect both the +ve and -ve terminals that the switches are soldered to? This is to rule out or prove that the problem is not the contacts in the switch?

Why not complain to the seller and get your money back?

Well, i paid about half retail for it, and besides, i was prepared to lose it in case i screwed up big time while desoldering and resoldering all the switches (and LEDs) on the board anyway. If it turns out to be a damaged trace, then hey - i could learn how to fix a damaged trace on a pcb!

[user 18]

Before you take a soldering iron to it, try shorting the pads on the PCB to see if you can get the key to register that way. If you can't, that would be indicative of a damaged trace, which is a more difficult repair process than swapping out a damaged switch.

When you say shorting the pads, i assume you mean use a copper wire (or similar) to connect both the +ve and -ve terminals that the switches are soldered to? This is to rule out or prove that the problem is not the contacts in the switch?

Yes, essentially. If the key registers when you connect the pads directly, you know the problem is with the switch or the solder joints. If the key does not register, your switch may still work just fine. In that case, you would need to follow the trace on the PCB to try and circumvent the damage with a jumper wire or two.

[myotherteeshirt]

More

Before you take a soldering iron to it, try shorting the pads on the PCB to see if you can get the key to register that way. If you can't, that would be indicative of a damaged trace, which is a more difficult repair process than swapping out a damaged switch.

When you say shorting the pads, i assume you mean use a copper wire (or similar) to connect both the +ve and -ve terminals that the switches are soldered to? This is to rule out or prove that the problem is not the contacts in the switch?

Yes, essentially. If the key registers when you connect the pads directly, you know the problem is with the switch or the solder joints. If the key does not register, your switch may still work just fine. In that case, you would need to follow the trace on the PCB to try and circumvent the damage with a jumper wire or two.
[/quote]

Okay, i get that. I'll try that tomorrow, and if it doesn't work, i suppose i'll ask again with pictures. Thanks!

[myotherteeshirt]

Well, dug out the old multimeter, and the switch is working. Am putting up a picture of the back of the pcb, maybe someone can spot the problem?



It's the switch on the lower left corner of the board, to the left of R44

[myotherteeshirt]

Well, I did some more prodding with the multimeter and there is no connection between the switch leg on the left and the thingy (I would say resistor but it's labeled D193 - diode?) immediately to the left of it.

 

I assume I have to bridge the gap between the two? Any instructions and tips would be appreciated - especially tips on tiny tiny soldering. Just eyeballing it, the pad that the resist-ode is on looks to be barely 2mm˛.

[user 18]

D for diode, R for resistor. There are both on that board. Diodes are used for the key matrix, resistors are used for LEDs.

If you're still looking for advice in a couple of days, I'll have more time to write a longer post soon.

[myotherteeshirt]

Okay, i'll wait for your reply before i attempt anything.

Meantime, i'll read up on circuitry and stuff. Any good resources to recommend? Really, my goal in this is to eventually build my own keyboard with parts from winkeyless.kr, and i guess learn to be able to make minor electronic repairs around the house.

I'll also just keep adding questions not directly related to fixing the connection below, and hopefully someone can find time to answer or point me in the right direction.

1st Round of Qns:

Q. The plate is really badly maintained, i'm thinking it could use a new paint job. Any recommendations for removing the paint and rust and repainting it? Do i just sand it off with sandpaper, or should i seek out professional services? Any recommendations on paint as well?

Q. I may consider powdercoating, if its not too expensive. Still reading up on that, any pros/cons of doing that on a keyboard plate?

Q. I assume the plate would be removable once i remove the switches and LEDs?

Q. Some of the solder joints look.. tarnished, when i do replace the switches & LEDs, should i do something about it or are they fine as is?

[dr_habu]

The soldering work on that board looks pretty weak. I'm actually surprised - I expected better from CM.

You can try bridging the gap with a pencil. It's a temporary solution, but it'll help you make sure that this is where the trace is broken.

[myotherteeshirt]

A pencil? That's neat, I wasn't aware graphite was conductive. Bridge the gap with pencil lead and test with a multimeter?

[dr_habu]

The pencil method was often used in GPU overclocking community for voltage mods(they used it to short traces and pads), so it might work here as well. I mean it's easier and quicker than soldering and it'll help you make sure that that's the actual trace that's broken.

[Kad]

The soldering work on that board looks pretty weak. I'm actually surprised - I expected better from CM.

You can try bridging the gap with a pencil. It's a temporary solution, but it'll help you make sure that this is where the trace is broken.

That's a neat trick. And OP, if you bought the board for much less than retail price is it possible the seller gave it away that cheap because of the fact that it was damaged?

[myotherteeshirt]

The soldering work on that board looks pretty weak. I'm actually surprised - I expected better from CM.

You can try bridging the gap with a pencil. It's a temporary solution, but it'll help you make sure that this is where the trace is broken.

That's a neat trick. And OP, if you bought the board for much less than retail price is it possible the seller gave it away that cheap because of the fact that it was damaged?

Sure, but i wasn't expecting a new board, i just didnt expect it to be *this* bad.

Other than some dustiness (it looks like they took off the keycaps and gave it a good brushing) and a small 5mm square patch of rust on the plate (and shine on wasd keys), the top and outside of it was within what i was expecting.

I honestly don't think this person was aware of anything other than the faulty enter key, because most of the surprises came from the back of the board. If you look at the joints below R82, i think you can clearly see the solder is dark, dull grey. There is a lot of this.

Quick question - how do i identify the polarity of the LEDs?

[Kad]

Longest leg is positive. If the legs have been cut even, there's a flat part of the "bulb" that shows negative.

[myotherteeshirt]

Longest leg is positive. If the legs have been cut even, there's a flat part of the "bulb" that shows negative.

Thanks for the advice. Is there any guideline to figuring out which is the corresponding hole on the pcb, or do I just make a note before I start removing them?

[suicidal_orange]

A pencil? That's neat, I wasn't aware graphite was conductive. Bridge the gap with pencil lead and test with a multimeter?

If you have a soldering iron anyway you'd may as well connect it permanently.  I'm not saying the pencil won't work (I did a GPU mod with one back in the day )) but that connection should definitely be there and there's no harm having two.  I like to use single core wire for matrix repairs - bend it into shape so that it touches both points you're connecting, then solder the switch (easy) end and lastly the diode end.  The diode will stay put as the other end is soldered.  If it's small distance like this a pair of tweezers to hold the wire is helpful.

If you look through the side of the LED there's a big side and a small side with a diagonal split between them, usually they all go the same way (all big sides on left or right) so you could write them all down before removing, or maybe only write down the ones that go against the norm.  If you're in any doubt solder near a computer so you can plug it in and touch the LED to the pads and confirm before soldering - if you put them backwards they won't light up, there's not enough power to do any damage.  Be sure to unplug it before soldering though.

If you don't like the soldering (it doesn't look great) then you could reflow every joint by adding some flux, but if you're thinking of taking the plate out you'll have to resolder everything then so not sure it's worth it.  As to the paint/powder coating the thing to be aware of is the thickness - if it gets into the switch holes the switches may no longer fit through.  If this happens you'll need many hours with a small file to remove the paint from the holes...  It may look nice but how much plate can you actually see between the keys? 

[dr_habu]

If you have a soldering iron anyway you'd may as well connect it permanently.  I'm not saying the pencil won't work (I did a GPU mod with one back in the day )) but that connection should definitely be there and there's no harm having two.  I like to use single core wire for matrix repairs - bend it into shape so that it touches both points you're connecting, then solder the switch (easy) end and lastly the diode end.  The diode will stay put as the other end is soldered.  If it's small distance like this a pair of tweezers to hold the wire is helpful.

Of course myotherteeshirt will proceed however he wants, but I if he doesn't have too much experience with a soldering iron then it's better if he only uses it where necessary. Without experience there's the risk that he'll overheat the PCB and do damage that's more difficult to fix(or actually work around). I mentioned the pencil method so that he could relatively easily make sure which points require fixing(it's possible that the trace is broken somewhere else, hell, it might even be broken in more than one place), and only solder where necessary.

I also wanted to mention that it's best to tin the wire(even single core) before you actually start trying to solder it to the pads on the PCB.

[myotherteeshirt]

I tried the pencil lead, maybe I'm doing it wrong, but it doesn't work. Will get some copper wire and try bridging the gap. Would enamel coated copper wire work?

Secondly, there looks like a lot of rust!


Started pulling out the switches and LEDs to try and clean the plate, and they look rusty. Are they, or is it just me? Any idea what may have caused this?

[dr_habu]

Enamel coated copper wire is used for coils. The enamel is actually an insulating layer of polymer. I will probably work, but I personally wouldn't use it for something like this, because you can't easily strip the insulation where you don't want it(so it might make the soldering more difficult an less reliable) and it's also very thin so I'd be worried that the wire might get scratched and short something that I don't wan't it to short. Someone more knowledgeable will probably correct me if I'm wrong on this.

If the pencil thing didn't work then I'd check to make sure that that's the only place where the traces are broken.

I also wouldn't worry too much about the colour of the led leads, I think it's just a matter of the alloy that the leads are made out of.

[myotherteeshirt]

Insulated wire, and don't worry about the LEDs. Got it.

What I did with the pencil lead was literally lay it across the two joints and test it with the multimeter, so I'm almost certain I did it wrong. I thought maybe I should have soldered the lead to the joints, but that seemed equally as odd as just laying the lead across, so I didn't attempt that.  I'm sure I was doing it wrong.

Anyway, have removed the plate, and now am gonna try to clean it. One suggestion I had was just sanding down the rusted parts with fine grit paper and painting it over.

Any other suggestions on how to deal with a rusty plate?

Would have attached pics, but attaching pics from my phone doesn't always work.

[dr_habu]

It's impossible to asses the degree of corrosion without pictures. If it's not too bad then using sand paper would probably be ok. If you decide to go that route then it'll probably be easier and faster if you use a more coarse sand paper first and then move to a finer grain.
I would probably sand blast the whole thing, but it's just being pedantic if the corrosion isn't too bad.

Remember to clean the whole plate with rubbing alcohol before painting it, use latex gloves while cleaning it. Make sure that there are no finger prints, dust particles or other contaminants on the surface. Paint it when you're sure it's clean. Also be careful when painting switch mounting holes - either mask it and don't paint it at all, or mask it after applying the first layer. If you don't then you might find out that the switches don't fit the the mounting holes any more and you'll have to carefully scrape the paint from the inner surface of the mounting hole cutouts with an exacto knife.

As always I'm sure that someone more knowledgeable than me will correct me if necessary.

[myotherteeshirt]

Pics:





Sandblasting? No? Vigorous sandpapering? Nonchalant ignoring?

[dr_habu]

I'd say that you can ignore it if you're ok with it. I mean it doesn't affect the functional aspects of the keyboard, but it might get worse with time and pieces of rust might start flaking off.
If you do decide to clean it up then like I said - I think that sand blasting is the best and the most thorough way to do this, but it's also the most expensive. Sand paper is obviously cheaper, but then again manual polishing of that plate will be very time consuming, so in the end you'll have to decide yourself which option is best for you.

The rust looks pretty deep in some spots, so I'd probably go with sandblasting, but like I said - you'll have to decide for yourself(and I'm sure you'll clean it up adequately yourself if you can't afford sand blasting).

[Herothereu]

Beer spill big time!