Simple way to bring back vintage keyboard back to life?

[Idner7]

I got vintage key monterey k 108,some electrical mybe broken,3led on for 1 sec then off,no signal input...
Simple way to fix this keyboard or new componen part to hack this key...?
Sory for my bad english

[Findecanor]

Welcome to Geekhack and congrats on the keyboard!
There is no simple fix if you don't know what the problem is...

If yours is a version has a XT/AT switch, make sure it is in AT mode before you plug it in/turn on your computer.
Remember that the interfaces with DIN plug do not hot-swap, but it should be safe to use a converter to USB and hot-swap the USB plug.

If that does not work, you would have to open it and look inside.

[Idner7]

Its open already,no bad element,only switch a x get rusty...
I thnk some componen is broken...
If i buy ic part for another keyboard form new gen can its work again?

[Findecanor]

If the AT/XT switch is rusty then I think that is likely to be the faulty component. You could replace it with a jumper wire shorting the lines for the AT mode and see if that works.
Be aware of what kind of switch it is and what terminals are connected where. Some switches short two individual pins to one-another, while others connect one outer pin to a middle pin when pressed.

If the LEDs come on now when you plug it in then the existing microcontroller should be working.
Check also the signal leads from the microcontroller to the port and plug. You could test that with a multimeter.

Replacing the controller would entail quite a bit of work. There is a steep learning curve before you would get started. There are several threads about putting new controllers in old keyboards. It would require rudimentary knowledge of electronics before you get started, reverse-engineering the keyboard matrix and then programming the microcontroller with a custom firmware with the matrix.