Author Topic: (HELP!) Pre-built PCB Testing (Ajazz K870T)  (Read 544 times)

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Offline onionown

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(HELP!) Pre-built PCB Testing (Ajazz K870T)
« on: Wed, 03 February 2021, 08:30:41 »
Hi, my brother bought an Ajazz K870T which is a TKL and has a soldered PCB and when it arrived, out of curiosity I tried testing the PCB with a tester with the tweezer method while it was still soldered and when I did that, the entire row lit up in the tester for some reason but the keyboard worked normally. Now he wanted to change out the switches so I tried to desolder it and I believe that i messed up a few times (i hate myself for this) and I want to test all sockets if everything is still working but the same thing happens when I try testing it (entire row lights up, e.g. i touch the socket of G key and the entire row lights up). Is there any other way to fix this issue or any other way to test the PCB if everything is still working without soldering every switch back? Thanks

Side note, all the LEDs on the PCB are working fine even after my desoldering catastrophe.
Thanks!
« Last Edit: Wed, 03 February 2021, 08:52:42 by onionown »

Online nevin

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Re: (HELP!) Pre-built PCB Testing (Ajazz K870T)
« Reply #1 on: Wed, 03 February 2021, 10:19:24 »
not sure how the pcb is designed, but a switch is noting but completing a circuit. so using tweezers or a wire to make a connection where the switch was is a way to test it.

depending on how the desoldering went, you may have some lifted pads (pretty common). in that case you'll have to figure out how it's wired and add some jumper wires once you have the new switches soldered in.

manufacturer's don't always follow how we typically make keyboards (the way we would wire the rows & columns). so get a multimeter that you can do a continuity test to poke around the board to try to figure out what goes where (how it's wired).

the leds lighting up....
either you were accidentally shorting the lights as well as the switch with the tweezers, or maybe the leds have a trace/pad in common with the switch or something. again, who knows how they implemented it.

it will be easier to see which switches are having issues once the new switches are in and when you type, they don't respond.

i did a google search for "diagnose fix broken trace keyboard pcb" and came up with a handful of relevant results, take a look to get yourself familiar

or you can browse around here, i've helped a couple people with the same problem here on the forum. i know at least two were dz60's, don't remember what the others were.
« Last Edit: Wed, 03 February 2021, 10:25:10 by nevin »
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Offline onionown

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Re: (HELP!) Pre-built PCB Testing (Ajazz K870T)
« Reply #2 on: Wed, 03 February 2021, 10:37:31 »
Hi, thanks for the reply.
I tried testing the PCB with the tweezer method both before (while the switches were still soldered to the PCB) and after desoldering the entire PCB. Both times when I would test a socket, the entire row it's in. I've heard about using jumper wires on PCBs, do the switches need to be soldered in specifically for it to work? Sorry I'm not that familliar with electronics hence the PCB-centric questions.
What I meant by all the LEDs on the PCB works is that I was afraid that I might've broken the PCB after the entire desoldering debacle, so since its a Bluetooth capable keyboard, I plugged in the battery and turned it on and all the LEDs were working fine.
I also did a quick google on lifted pad/s, are there conductors in the walls of the hole were the switch pins go in? or is it just on the front and back surface of the PCB? If that's the case, I believe this might be the problem I'm worrying about since some of the switches I got off the PCB seems to have leftover solder + what I believe to be some sort of thin conductor, copper most likely I'd say.

Just additional information, it's my first time working on a solderable PCB so clearly I lack the appropriate knowledge to be working on one hahahaha

Online nevin

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Re: (HELP!) Pre-built PCB Testing (Ajazz K870T)
« Reply #3 on: Wed, 03 February 2021, 10:43:19 »
yes, the inside of the hole is usually plated as well, whether it does anything on the other side depends on how the pcb was designed. some run columns on one side and rows on the other side...

my suggestion... clean it up, solder the new switches in, and see what's not working. then you can add any needed jumpers to get the non working switches to register again.
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Offline onionown

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Re: (HELP!) Pre-built PCB Testing (Ajazz K870T)
« Reply #4 on: Thu, 04 February 2021, 02:08:48 »
Alright will do that, what kind of wires or cable do you recommend for me to use? I've seen mix things on the internet.
Thanks again!

Offline suicidal_orange

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Re: (HELP!) Pre-built PCB Testing (Ajazz K870T)
« Reply #5 on: Thu, 04 February 2021, 03:36:29 »
Any wire will do, it can't be thinner than the traces on the PCB.  Common choices are old network cables and old IDE (hard drive) cables.  Stiff (single core) wire stays in place but risks pulling off pads if you pull on it so bendy (stranded) is usually preferred.
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Offline onionown

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Re: (HELP!) Pre-built PCB Testing (Ajazz K870T)
« Reply #6 on: Thu, 04 February 2021, 07:19:32 »
Alright, thanks everyone for your responses, will update the thread once I'm able to try it out.