H765 Power System

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The H765 Power System is a modular power supply system from DEC, used in the BA11-K mounting box and variants thereof. In addition to main memory and device controllers on other PDP-11's, the BA11-K was used to hold PDP-11/04 and PDP-11/34 CPU's.

The main transformer in the H765 supplies 20-30V AC to several DEC standard modular regulators (up to four, in spaces numbered '1' through '4') mounted in the H765, which provide other voltages such as +5V DC to the backplanes in the mounting box.

Generally the power harness supports only a fixed arrangement as to which regulator can be in which spaces; e.g. the BA11-K harness mandates that #2 and #3 hold H744 +5V Regulators, #1 holds an H745 -15V Regulator, and #4 may hold an H754 +20V, -5V Regulator.

70-10138 harness

A 54-11086 board in the H765 supplies a modest amount of +15V DC power to various backplanes mounted in the BA11-K, along with a line time clock signal, and AC and DC 'power OK' signals. A special 70-10138 harness is used to connect the edge finger connectors of the 54-11086 to the power distribution board in the BA11-K.

The BA11-K harness used DEC power distribution connectors to provide power to standard backplanes; it normally used the DEC standard power wire colour coding.

When the BA11-K box is used in custom configurations to hold other sub-systems (such as the MJ11 and MK11 memory systems), other regulator configurations may be used (e.g. the MJ11 calls for two H744's and two H754's), along with a custom main harness, and harness to the 5411086.

The H765 runs off standard wall AC; it can be jumpered to use either 110V or 220V supply. It supported the standard DEC Remote Switching Control Bus, so it could be turned off and on from a power switch elsewhere.


Some components on the 54-11086 board are not protected by a fuse; if they fail 'closed', since AC to that board enters through contacts on the edge connector, those contacts may be damaged.

See also