Digital Rainbow PC100B Power Supply

The Digital Equipment Corporation Rainbow PC100 is an odd amalgamation of a VT100, Z80-based CPM computer, and early DOS PC. It has both a Z80 and Intel 8088 CPU on the same motherboard an the system ROM also supports running as a VT100.

Wikipedia

Symptom or Problem Encountered
The circuit breaker immediately trips when power is switched on.

Causes

 * power transistor failed, shorting the 12V output to ground

Solutions

 * Replace the failed transistor and also a diode array that had also failed-short

Disassembly Notes
It comes apart really simply. 4 screws to take the top of the case off, two more to detach the IEC socket, then disconnecting plastic connectors to be able to get to all of the screws holding the board down. There was one security Torx screws (size?), the rest are #2 Phillips.

The parts that went bad for me are circled in this picture:

Basic PCB Name
Note model numbers and board revisions here

Basic PCB Name
If parts are not available or different selection is preferred, you can use the values in the Original Parts section to perform a parametric search.