[HELP] Nan Tan Keyboard KB-6153ER failure

[Oneminde]

Hello.
I recently got myself a Nan Tan mechanical keyboard which uses the famous yellow ALPS mechanical switches. The feeling is really fantastic and beats and Cherry switches.

However, it will not work. What happens is that when I start my PC, after BIOS start loading, the LED's flashes as it does with all keyboards, it turns dark or off again as normal, but never return as functional. So I initially thought it was the electrolytic cap (1) was old, so I replaced it (same value), but the same symptom is present. A flash and then nothing. It is plugged into the ps/2 port via an adapter. I tested it on two computers, same symptom.

There are two IC's on the board.

NTC6151N: Propitiatory Controller IC
GD74LS05: HEX Inverter.

My question is if anyone know how to start fixing the issue with the keyboard ?

--- EDIT ----
I am currently on an IBM Model M (1991) so I know the ps/2 port is functional.

[nidlaX]

Interesting! (Oops, just read the model number in your title.)

If it's AT-XT switchable, make sure it's switched to AT.
If you're using an AT to PS/2 adapter, make sure the adapter is not at fault.
Inspect the board for other physical issues such as broken traces, bad solder connections, etc.

If all else fails, you can always adapt the board using one of those microcontrollers that already has cookie cutter firmware.

[Oneminde]

Solders look good. I tested the switch in both the 8088 and 80286 position. I am using a 6 Pin Mini Din Male to 5 Pin Din. All solder joints look good.

If all else fails, you can always adapt the board using one of those microcontrollers that already has cookie cutter firmware.

Could you elaborate ?

[Oneminde]

I think I'll do the manual routing using Teensy board. Using the 1N4148 diode.

[nidlaX]

Is this your work? The hand wiring looks good!

[amyk]

The IC is probably an Intel 8048 or 8051 variant...  look at the pinout to be sure.

[Oneminde]

nidlaX: No its not my work, I found it via https://geekhack.org/index.php?topic=69841.0

amyk; could be, its a 40 pin chip.

I have already ordered 120 pcs 1N4148 diodes. Really looking forward to this mod. It might be the IC or both that has given up, but the mod is not that complicated and will give me a proper USB connection.

[Oneminde]

First part arrived.

As you know, I’ve decided to save it from an early grave since it got the sweet ALPS mechanical switches, which is superior to the Cherry MX line up.
What you are looking at is the 1N4148 diode. This is soldered to each switch. Diodes restrict the direction in which current can flow in the switch matrix. This allows one to build full NKRO keyboards (n-key rollover) and it also prevent ghosting which is several switching that send info simultaneously and this create communication error between the input and desired output. Diodes prevent this.