KM11-A Maintenance Set

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The KM11-A Maintenance Set (also variously called the KM11-A Maintenance Panel, KM11-A Maintenance Console and KM11-A Maintenance Cards in some later DEC manuals) is a device used to perform maintenance activities on early PDP-11 CPUs and some early PDP-11 peripherals.

As produced by DEC, a KM11 consists of a W131 Maintenance Indicator Module plugged into a W130 Maintenance Connector Module; later a W131 and a W133 Driver Module. The W131 contains an array of 28 lights, three double-throw switches, and a single spring-loaded double-throw switch.


A variety of overlays, specific to a CPU or peripheral, indicate the meaning of the lights, and the function of the switches, when used with that CPU or peripheral.

The CPUs which can use the KM11-A, and for which overays exist, are:

Devices which support the KM11-A, and for which overays exist, are:

There is also reportedly an overlay for the KE11-A Extended Arithmetic Element‎, but although several KE11-A documents refer to it, no image of it can be found.


A replica KM11 from Shiresoft

The original DEC KM11-A's are incredibly scarce, but they are also a very powerful diagnostic tool. So, there have been several different projects to produce replicas; see the links below.

External links