Need help with replacing cable in IMC XT/AT Keyboard

[ppCircle]

So i found this keyboard in old factory. I know it is in insanely dramatic condition but pcb looks fine. So im gonna try to restore it.
(i had permision to go there and pick up what i want)



The biggest problem is with cable. Somebody cut it off. And side that plugs into pcb have 6 pin conector and uses 5 cables. I personaly never seen something like that so im looking for help. What does that fifth cable do? It's some terminal reset line or something? And if i can just plug that cable that you can see on the left.

[ayehavgunne]

Oh my, so dirty. How are the switches?

[ppCircle]

Oh my, so dirty. How are the switches?

Not as bad as it looks. There is ton of dust inside them but after deep clean they feel just like alps without lube. Clickleafs are in really good condition.

[mike52787]

The 5th wire you ask about is probably reset, which was used with the XT protocol. That or a second ground wire (usually tied to the shield of the din connector)

[ppCircle]

Forgot to mention ground goes by separate cable to plate. Pcb is connected to it by that blue cable what is seen in pcb photo.

[ppCircle]

So i tried checking pinout with multimeter. That's the results.



As i am don't know anything about electronic i only figured out that fourth pin can be gnd and fifth is vcc (maybe?) because these side pin readings are weird. So im gonna wait for advice beffore im gonna starts doing something more. Maybe i do something wrong.

[PlacaFromHell]

Hello. If you can provide info about the keyboard model we might be able to find more information. Anyways, I will try to give you some help. At first, always the bigger and more robust trace in almost any circuit is GND, from what I see in your picture you should follow this trace:


If you want to find VCC just follow the components. Usually the IC's have the VCC and the GND traces one in each corner. I don't know what's under this piece of your PCB but in the picture looks like an IC and has two corners with very robust traces. It SHOULD (I'm not sure) be the VCC line.

Don't trust in the rule for the bigger specific IC's.

If you already found the VCC and GND, at this point if I'm correct you can safely try to search for the DATA and CLOCK traces just by swapping cables randomnly. The real risk is swapping VCC and GND and burn something.

[ppCircle]

Hello. If you can provide info about the keyboard model we might be able to find more information. Anyways, I will try to give you some help. At first, always the bigger and more robust trace in almost any circuit is GND, from what I see in your picture you should follow this trace:


If you want to find VCC just follow the components. Usually the IC's have the VCC and the GND traces one in each corner. I don't know what's under this piece of your PCB but in the picture looks like an IC and has two corners with very robust traces. It SHOULD (I'm not sure) be the VCC line.

Don't trust in the rule for the bigger specific IC's.

If you already found the VCC and GND, at this point if I'm correct you can safely try to search for the DATA and CLOCK traces just by swapping cables randomnly. The real risk is swapping VCC and GND and burn something.

I forgot to send picture of front panel of pcb.



I followed it "Usually the IC's have the VCC and the GND traces one in each corner" so that's why i said that it's probably gnd and vcc



All my worries for now are all about those huge readings from vcc compared to the rest

And about informations about keyboard, model etc. There is literaly none. I couldn't find any informations about it. All i know its name from badge, markings on pcb and made in taiwan label on the back

[PlacaFromHell]

Just to confirm, take this:



We're right about VCC and GND. is not so odd to read something between VCC and the rest of the pins if you have certain components in the middle, but not the most normal thing. If you want to check the integrity of the most suspicious components, check the capacitors continuity, you shouldn't be able ro read anything.

[ppCircle]

If you want to check the integrity of the most suspicious components, check the capacitors continuity, you shouldn't be able ro read anything.

They seems fine

[ppCircle]

So it took me a while because i had no time for keyboards in last 2 weeks, but i managed to make it alive when laying cables for the first time



Huge thanks for help, gonna make post about it when restoration gonna end