Exploring the elusive IBM 4680 POS Matrix Keyboard P/N 76X0100

Contents

Introduction

Here's an in-depth tour of the IBM 4680 POS Matrix Keyboard, an ortholinear-style relegendable point of sale terminal keyboard first announced in December 1987^[1][1]
IBM - IBM 4683 Point of Sale Terminal Models, Displays, and Enhancements Brief Description of Announcement, Charges, and Availability (#187-240) [accessed 2023-02-14].. Whilst this keyboard has been discovered and posted about on deskthority and geekhack before, I've not come across an actual teardown of the keyboard. Just like my exploration article on the IBM Model M7 POS keypad from last year, this article will be an unstructured and free-following affair with annotations available to provide context and help screen readers. All images can also be clicked to enlarge.

As a bit of background, the IBM 4683 was noteworthy for being the first PC-based point-of-sale (POS) retail system from the company. The keyboard was also used with IBM 4684 POS Controller Terminals as well. This keyboard was not the only large ortholinear-style keyboard from IBM - in fact, IBM was making the titanic 254-key IBM Multi-Shift Kanji Keyboards in the previous decade. But it's definitely an unusual sight from the company. This keyboard seems to be spiritually succeeded by the IBM Model M11 Modifiable Layout Keyboard (such as P/N 92F6290) in 1993, which was an IBM buckling sleeve keyboard with an integrated magnetic stripe reader originally made for the IBM 4694.

The box & the outside

Starting with the box, it's very spartan with a single blue IBM square logo, the number 5 written on various faces, and the serial number/part number sticker.

Inside the box, the keyboard is packed in a red-tint plastic bag and is secured with two foam rings on either side of the keyboard. The foam does a good job of securing holding the keyboard in the box.

Also in the box are two bags that contain a kit for making labels to put on the keycaps. In one bag, you get many paper sticks to write text onto, and in the other, you get many plastic 'window' covers.

Going back to the keyboard, the back sports four rubber feet, two mounting holes, a grille for the internal speaker, and several stickers indicating several part and serial numbers and proclaiming the keyboard was made in the USA.

The keyboard uses the same 8-pin ("POS") SDL connection that other IBM POS input devices such as the Model M7, M8, M9 and M11 keypads and keyboards also used. A standard Model M SDL connector has only 6-pins and will not fit properly in the socket.

To test the keyboard, I tried using an IBM P/N 42M5599 (P/N 54P8831 equivalent) 8-pin SDL to PS/2 cable that I know works with the later Model M7 and M8 POS keypads and... the LEDs light up but the keyboard is unresponsive. For reference, the cable I'm using has the following SDL-end pinout. I need to run more tests, but right now, it's possible that the SDL-end data and clock pins are different or it simply doesn't speak Set 1, 2 or 3.

The keycaps are well-textured and double-shot. Very nice keycaps, in fact.

The switches are the tactile variant of Key Tronic foam and foil capacitive switches. That said, I honestly thought these were just stiff linears when I first tried them. I have yet to open up a switch to check the foam.

On the inside

Here's the mainboard split into three photos. The left-side 2-pin connector is for the speaker, the right-side one is for a microswitch shown below.

An actual Micro Switch. It is used for sensing if the keylock is activated or not.

The speaker is rated 8 ohms, 0.2 watts.

Depending on your viewpoint, the mark of the beast.

Final remarks

I'm sure many will say it's a big shame that this keyboard uses Key Tronic foam & foil switches. Indeed, it's a cool looking keyboard and it's built fairly well. There's little flex in the case and the internal assembly is quite sturdy. In their current condition, the keys do not feel as bad as I've been told they can be. But, that could change since this is a switch that could literally rot (or, it could have rotted already). If you're wondering about the keyboard's metrics:

As aforementioned, I tried to test the keyboard with a modern PC to no avail. I'll be working on figuring out the keyboard in my spare time and I hope to write a follow up on this keyboard along with a proper assessment on the condition of the foam. Documentation for this keyboard is also very scarce, so if you happen to know anything about the keyboard (especially if you know how it communicates), please get in touch!

Cheers!

Corrections & changes

Sources