A spare KIM-1 keypad is even rarer than a KIM-1 itself. With this guide you can build a reasonable replica of the keypad. Updated 21 april 2026 with enhanced 3D STL designs.

Parts you need

• PCB as designed by Eduardo
• 19 SMD switches TL3305A
• A slide switch JS102011SCQN
• 2 Keypads, as source of keycaps scavenged from keypads sold as AZ-Delivery 4×4 Matrix Keypad, also available cheap on AliExpress.
• 3D STL of frame, either with ON text embossed or without (see below)
• 3D printer, black PLA filament or balck resin, depending on your 3D printer. Or send it off to a 3d printing service. I have used black PLA, my friend Gerben Voort a professional 3D printing service in resin and sanded.
• At least 3 small self tapping screws
• Several self tapping screws to connect the kaypad to the KIM-1 PCB from underneath
• A label printer like the Dymo Pocket with White on Black tape 9 mm

Step 1. Populate the PCB with switches

Get the PCB as designed by Eduardo Casino. The design is available at his github archive. Sent the gerbers to your favorite PCB factory, I use JLCPCB. Surface mount switches and slide switch. Solder one leg first of all switches. Check if the switches are nicely in line with the others. Move if required. Only when you are satisfied with the position of all switches, solder the other legs. Fine tip, not too much solder. Next solder the two wires (A to A, B to B) on top of the PCB.

Step 2. Print the frame and the slide switch button

Depending on your printer and wish to be close to the original a choice of two 3D designs has to be made:

1. The 3D design by Pete (peo2000 on forum64.org) You can print his one with the front on the bottom. No supports required, use fine resolution. That delivered on my 3 printer a quite smooth end result.
2. The design enhanced by me with the embossed text ‘ON’ like the original keypad of the KIM. And a small cutout, and ribbles on the SST switch This one needs to be printed with the front of the frame on top due to the embossed text. So it needs supports. This means quite some afterwork to remove the artefacts and the top is not as smooth.
The slide switch button is quite small, print in highest quality with a brim.

My friend Gerben Voort uses a 3D printing service. In resin black a near perfect result is achieved.

Step 3 Add the keys

The printed frame is meant to be used with keys scavenged from 4×4 keypads. Break the 4×4 keypad open and take the keys out. As you can see, keys 0,,9 and A..D can be used right away. The other keys (E, F, AD, DA, ST, RS, PC, +, GO) need a label. I print those with a cheap Dymo Pocket printer with white on Black 9 mm tape. The ‘E’ and ‘F’ are printed ‘wide’, the other in normal width. Cut the label to the right size and put them on the keys. I wish the color white was a bit more white, and the font more like the the other keys, but it is the best I can do with this label printer. Insert the keys in the frame with the frame top on the table. Put the slide switch button on the slide switch.

Step 4 Combine PCB and frame

You now have a PCB with switches and a frame with keys. Put the PCB on the frame and screw some small self tapping screws in the PCB into the frame.

The last step

Check if all keys ‘click’, as in this video.

Now you can mount the keypad on your KIM-1 with some self tapping screws from the backside of the KIM-1 into the keypad. Do not forget the wires on top of the PCB (A to A, B to B).

After publishing the photos of the transistors used in the KIM-1 a discussion started on forum64.de in the ‘Instandsetzung und Nachbau eines Kim-1’ thread about some transistors were placed wrong in later revisions. And the KIM-1 involved functions well.

The User manual states:

 --------+-------------------+------+---------------------------------------
 | ITEM  | PART              | QTY. | DESCRIPTION                          |
 +-------+-------------------+------+--------------------------------------+
 |  18.  | Q7                | 1    | NPN Transistor B>20, VCE>12 - 2N5371 |
 |  19.  | Q1 through Q6     | 6    | PNP Transistor B>20, VCE>6  - 2N5375 |
 --------+-------------------+------+---------------------------------------

which are quite generic general purpose transistors.
MOS Technology used those parts in the first edition, Rev A and Rev B. Commodore then took over and parts used changed to equivalents.

In my KIM-1 collection I have found (see also the list in this page, Q1..Q6 also have this quirk on some KIM-1s)

Transistor Q7

Rev D 2N3904
Rev E 2N3904
Rev F 2N4401
Rev G 2N4401
Rev G 2N4401

which are functionally equivalent, but have a different pinout. But are placed exactly like the 2N5371.

My first KIM-1, Rev F has a BC239C, which is OK, my trusty old KIM-1, functioning perfectly over the serial interface with thsi CBE transistor.

The 2N5371 pinout is CBE, Collector Base Emitter. The 2N3904 and 2N4401 are EBC.

The actual pinout of the 2N5371 is CBE. The letters in the image are beneath the actual wire, and the Base wire is bent to the back.

Those are EBC pinouts. But they are placed exactly like the 2N5371, which is CBE. It should be the other way around. But it works!

On the Rev D Replica by Eduardo Casino and the Nachbau KIM-1 by Ralph02 the BC327(2N5375) and BC338(2N5371) are used. These have the same pinout.

How does that work?

Well, it seems that it does not matter here. An NPN transistor can be wired this way, exchanging Collector and Emitter. It functions the same, but the specs are much worse like the amplification factor. Since this is an emitter follower and the input voltage can be (via a limiting resistor to be added) go to 5V it works reliable.

Even a microprocessor based computer as the KIM-1 required some simple transistors.
To drive the LEDs some extra current is needed, so there are 6 PNP transistors there.
And in the serial circuit an NPN transistor is used.

The User manual states:

 --------+-------------------+------+---------------------------------------
 | ITEM  | PART              | QTY. | DESCRIPTION                          |
 +-------+-------------------+------+--------------------------------------+
 |  18.  | Q7                | 1    | NPN Transistor B>20, VCE>12 - 2N5371 |
 |  19.  | Q1 through Q6     | 6    | PNP Transistor B>20, VCE>6  - 2N5375 |
 --------+-------------------+------+---------------------------------------

which are quite generic general purpose transistors.

This is what I found in my KIM-1s. The first ones, made by MOS Technology, to Rev B, used the 2N5371 and 2N5373. Thereafter it seems any useable and available transistor was used.

Q1 tot Q6 LED drivers PNP general purpose transistors

First edition 2N5375
Rev A 2N5375
Rev B 2N5375
Rev D B564 MI58 (which actually is a 2SB564)
Rev E B564 MI58
Rev F 2N5375
Rev F BC327
Rev G 2N4403
Rev G 2N5375

Q7 serial circuit NPN general purpose transistor

First edition transistor missing in action, only a socket!
Rev A 2N5371
Rev B 2N5371
Rev D 2N3904
Rev E 2N3904
Rev F BC239C
Rev F 2N4401
Rev G 2N4401
Rev G 2N4401

On the Rev D Replica by Eduardo Casino and the Nachbau KIM-1 by Ralph02 the BC327(2N5375) and BC338(2N5371) are used.
The Micro-KIM and PAL-1 and PAL-2 use the 2N4401 and 2N4403.
The KIM-1 Reproductions by Dave Williams a BC338 and MPSA92.