After [David Lovett] of [Usagi Electric] was donated a few cars full of DEC PDP-11 minicomputers of various flavors and vintages, he passed on most of them to loving homes, but kept a few of them himself. One goal of this being to put together a PDP-11 system that could be more easily taken to vintage computer shows than the ‘rollable’ PDP-11s he had access to prior. Of 1980s PDP-11s, the first-generation Large Scale Integration (LSI) PDP11/03 system (so-called Q-Bus models) is among the smallest, taking up about as much space as a 1980s desktop PC, while supporting the second generation LSI PDP-11/23 cards. It all seemed so easy until [David] tried testing the PDP-11/03’s PSU and everything went south.
Despite having access to the circuit diagrams of the PSU, figuring out what was going wrong was an absolute nightmare for [David], after some easy fixes involving replacing a blown fuse and bulging capacitors failed to deliver salvation. Reading through the comments to the video, it would seem that people are generally confused about whether this PSU is a linear, switching or some other configuration. What is clear is that with the absolutely massive transformer, it looks more like a linear power supply, but with a lot of protections against over current and other failure modes built-in, all of which rely on transistors and other components that could have gone bad.
Although in round 1 the PDP-11/03 PSU won the battle, we hope that once round 2 commences [David] will have had the proverbial training montage behind him (set to ‘Eye of the Usagi’, probably) and will manag ..
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