BA11-A mounting box

The BA11-A mounting box is a 10-1/2" mounting box; the terminal variant letter notwithstanding, it is just about the last in the line of BA11 mounting boxes. It was introduced with the PDP-11/44, and was also used with the PDP-11/24 and VAX-11/730.

Unusually for PDP-11s, its integral power supply also provided +12V/-12V DC, used for the MS11-M MOS memory's MOS memory chips.

It came with the H7140 Power Supply (PDP-11/44) or H777 Power Supply (PDP-11/24), mounted at the rear of the box. There were four main variants, depending on the input AC voltage, and details of the secondary output:

Model	Input	Memory voltages
-AA	115	+12V, -12V
-AB	230	+12V, -12V
-DA	115	+12V, -15V
-DB	230	+12V, -15V

Maximum power was 1350W with maximum load applied; it could provide 120A of +5V, and 10A of memory refresh +5V power to MOS memory; 3A of +15V, 3A of -15V; and 5A of +12V, 1A of -12V or -15V.

The H7750 Battery Backup Unit, which provided refresh power during brief power outages to MOS memory mounted in the BA11-A, was an option.

Power connections

PDP-11/44 setup

The BA11-A does not use only the standard DEC power distribution connectors; it also provided special connections on bus bars in its power supply, and in some applications (e.g. the -11/44's KD11-Z CPU), the CPU's backplane uses unique Flexprint cables for power, which go to the special connections (see image).

For backplanes which did not have the Flexprint cables (e.g. that of the -11/24's CPU), including the DD11-DK, DD11-CK, RK11-D, etc., a special 'Power Distribution Board' (DEC part number 54-13815 for the 11/24 or 54-13632 for the 11/44) mounts to the bus bars and provides the needed Molex connectors.

External links

• BA11-A Mounting Box and Power System Technical Manual (EK-BA11A-TM-003)
• BA11-A Field Maintenance Print Set (MP00832 - May '79)
• BA11-A Field Maintenance Print Set (MP00832 - Apr '87)
• Repairing a H7140 power supply - informative blog entry on repairing an H7140 power supply
• Fan Overhaul BA11-A