Monogram SMK derivative keyboard restoration

browncow · 28 Nov 2023, 13:59

Hello, I have recently gotten sick so, having some spare time at my hands i've decided to have a go at restoring one of my weirder boards, this thing:

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It has the "monogram" switches, a clicky variant, very interesting and pleasant to me but they were a bit scratchy, so i decided to desolder everything, take apart, ultrasonic clean and lube with just a little bit of trybosis 3203 (i tried krytox and it made it worse), seems like these switches need thinner lube, trybosis has worked really well, definitely an improvement. Retrobrighted the keys (very nice doubleshots by the way), the case is very yellow and i'm not sure if it will come out that good but we'll see.

: IMG_20231128_132436.jpg (832.09 KiB) Viewed 4953 times

Keys have brightened up nicely

The switches were quite hard to put back together, as the contacts are like simplified alps, separate pieces of metal, and you have to kind of, guide them into the top housing and be careful when pushing the housings back together, but it's still much easier than simplified alps, because everything is just bigger. Now here's the kind of interesting bit:

: IMG_20231128_132446.jpg (898.15 KiB) Viewed 4953 times

The board has a place for a piezo buzzer, it looks like it requires another transistor, which i am not sure but could be the same as Q1, pictured here:

: IMG_20231128_132511.jpg (755 KiB) Viewed 4953 times

And two additional resistors. I figure they wouldn't bother to flash different firmware for the buzzer/not buzzer version of this board most likely, so it wouldn't hurt to try soldering that hardware back on

Does anybody have a simmilar board, but with a buzzer, or, help me figure out the values for the resistors somehow? It would be quite funny to make this thing beep.
Cheers.

Muirium · 28 Nov 2023, 15:36

Commendably white spacebar for a doubleshot set. Surely it's ABS too?

Only board I have with a beeper is my Kishsaver. I’m thankful for its volume dial, as I have it turned right down. Definitely bear a volume control of some sort in mind for yours.

jsheradin · 28 Nov 2023, 17:56

Buzzer would be pretty neat if it's actually enabled in firmware. You should be able to check for a signal on whatever pin goes between Q2 and the controller. If you see a square wave blip when you push a key then you're good to go.

Do a bit of reverse engineering and figure out which pins are CBE for Q2. Not all transistors use the same pinout annoyingly. It's going to be either an NPN or PNP. You'll be able to tell based on if it's doing high or low side switching. A suitable part is probably the 2N2222 or 2N2907.

Spoiler:

Resistors might be a bit harder to figure out. You can try 1k for both of them first and just see how it works. I'd bet the circuit is just the basic totem pole:

Spoiler:

browncow · 28 Nov 2023, 18:59

jsheradin wrote: ↑
28 Nov 2023, 17:56
Buzzer would be pretty neat if it's actually enabled in firmware. You should be able to check for a signal on whatever pin goes between Q2 and the controller. If you see a square wave blip when you push a key then you're good to go.

Do a bit of reverse engineering and figure out which pins are CBE for Q2. Not all transistors use the same pinout annoyingly. It's going to be either an NPN or PNP. You'll be able to tell based on if it's doing high or low side switching. A suitable part is probably the 2N2222 or 2N2907.

Spoiler:
1635273600709-pnp_npn_switching-outputs-771823061.jpg
Resistors might be a bit harder to figure out. You can try 1k for both of them first and just see how it works. I'd bet the circuit is just the basic totem pole:

Spoiler:
ZDPX8m.jpg

Thanks a lot for the reply! i will give it a try and report my findings.

browncow · 04 Dec 2023, 19:13

jsheradin wrote: ↑
28 Nov 2023, 17:56
Buzzer would be pretty neat if it's actually enabled in firmware. You should be able to check for a signal on whatever pin goes between Q2 and the controller. If you see a square wave blip when you push a key then you're good to go.

Do a bit of reverse engineering and figure out which pins are CBE for Q2. Not all transistors use the same pinout annoyingly. It's going to be either an NPN or PNP. You'll be able to tell based on if it's doing high or low side switching. A suitable part is probably the 2N2222 or 2N2907.

Spoiler:
1635273600709-pnp_npn_switching-outputs-771823061.jpg
Resistors might be a bit harder to figure out. You can try 1k for both of them first and just see how it works. I'd bet the circuit is just the basic totem pole:

Spoiler:
ZDPX8m.jpg

I did poke around and go along the traces, and i noticed one of the traces that would be triggering the transistor, is connected to a place on the pcb that looks like a placeholder for an 8pin chip of some sort. So i guess no luck. I guess i would have to bump into somebody who is in a possesion of keyboard with that pcb, with the missing bits on it... Thanks for help anyway! on the bright side, i have completed the restoration, and the properly cleaned and lubed switches make a HUGE difference, even though pain in the ass to assemble i think it was worth it

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