It all started on the VCFED forum many years ago, where people were looking for help on repairing their KIM-1 computer.
A dead KIM-1 is no easy to troubleshoot, most ICs are not in IC sockets, so poking around with a scope is looking for dead signal lines is all you can do.
But if the 6502 is working, programs could be written to test parts.

So Dwight Elvey designed and programmed a diagnostic board for the KIM-1, to determine what might be wrong with this KIM-1.
The board switches off the 6530 ROMs and one can run tests on the onboard ROM, looking for for defective RAM, defective LED display, defective 6530 ports.

Here I present the complete design of the board, with help and permission of Dwight Elvey, Santo Nucifora and Liu Ganning.
In October 2025 I have revised the page, build a diagnostic board myself and added the reverse engineered sources of the tests in MOS Technology standard assembler syntax instead of the obscure Forth like assembler Dwight uses. The EPROM can now be build and modified with modern tools.

The board has been used by many with success. The usual suspect, the 6530-002 RRIOT, was not always the problem maker. Defective RAM IC, a TTL IC with dead ports and such also were found
by using the test programs to pinpoint the area to check.

I know of seven KIM-1 revisions, labeled Rev A-G and the first one unlabeled. Rev C is unknown!

What changed between these revisions?

Not much. The PCB underwent several changes around the logo area, from KIM-1 MOS to Commodore C-MOS. That happened from Rev A to Rev D, indicating the takeover by Commodore of MOS Technology. And some small numbers/artefacts etched in various Revs.

Some have serial numbers, the first ones on the back on the right, later had stamped/written numbers like PAxxx (Palo Alto) and SCxxx (Santa Clara) of Commodore production facilities

There was a change in the PCB from Rev A to B.

Another change appeared going from Rev B to Rev D. The keyboard changed, the SST switch moved to the other side. And there were some extra holes required for the new keybaord, some traces needed to move also.

The User Manual went from version 15 (January 1976) to 15A (March 1976) to 15B (August 1976) without significant changes, mostly typing errors and the change of keyboard from Rev B to Rev D.
The keyboard changed from rev B to Rev D. The SST switch moved to the other side, the first Rev keyboards were not very reliable.

What did not change?

The 6530 – 002 and -003 were from many different dates between 1976 and 1980. The functionality stayed the same, no software changes are known. It seems the same mask was used to produce another batch due to the demand for KIM-1s. On Rev F and G I have seen older 6530s (ceramic ones) from much earlies dates, old stock being used?

The large Circuit Diagram poster stayed the same for all revisions.

Parts used

The parts used in all these revisions changed from as much as possible made by MOS Technology (6102) to industry standard compatible types (2102). E.g the RAM ICs were all third party in later revisions.
The capacitors, mostly yellow tube types, also came in various colors and sources between revisions.

Except for Rev G no IC sockets were used.

Before I saw the last revision, Rev G, I had never seen an original KIM-1 with IC sockets. All ICs were soldered right into the PCB.

Now I have a KIM-1 Rev G and a photo by Dick Dral of his KIM-1 Rev G with white IC sockets.

So the last iteration of the KIM-1 did have IC sockets.

Not only did Rev G come with sockets, they used not only white sockets, black ones too (Thanks Santo Nucifora).

In 2024/2025 I completed my KIM-1 collection with one or two from every Revision, from first edition to Rev G, nine in total.

I have so far found 5 versions of the KIM-1 User Manual.

First Edition January 1976
Second Edition March 1976
Second Edition August 1976
Rockwell branded version 1977.
German version 1977
Only small updates, some errors, and the change of keyboard with SST switch right to left.

All available here: KIM-1 manuals and MOS Technology documents – Retro Computing