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Likely PSU rating for Novy 020/030 accelerator?
Posted by: Byrd on 2025-12-31 04:49:39 Hi, I’ve an early Novy 68020 accelerator in a Mac Plus, I’ve had it piggybacked off the Plus motherboard harness +5V and experiencing power issues. The Plus analog board is recapped and with the accelerator running it takes a few power cycles to get it running, voltages are rock solid but I feel running the accelerator is putting it under strain. With the accelerator removed the Plus functions fine. I think most of these early 020/030 accelerators had a small PSU inside the case; what voltage and amp rating were they? I’m thinking of doing same or running the power brick out the back potentially as a trial. Thanks
Posted by: Realitystorm on 2025-12-31 07:10:07 From my quik30 plus. 5v, 2a, 17w
Posted by: Phipli on 2025-12-31 07:11:32 Hi, I’ve an early Novy 68020 accelerator in a Mac Plus, I’ve had it piggybacked off the Plus motherboard harness +5V and experiencing power issues. The Plus analog board is recapped and with the accelerator running it takes a few power cycles to get it running, voltages are rock solid but I feel running the accelerator is putting it under strain. With the accelerator removed the Plus functions fine. I think most of these early 020/030 accelerators had a small PSU inside the case; what voltage and amp rating were they? I’m thinking of doing same or running the power brick out the back potentially as a trial. Thanks If the 5v is stable it probably isn't the issue, but if you want to test you could power the accelerator from an external 5v by running two wires from an empty hard disk enclosure perhaps? Remember to connect 5v and gnd, and you must isolate the accelerator from the Plus' 5v! Then I'd just buy a small 5v Meanwell power supply or similar. Anything 2A or a bit more will be enough based on @Realitystorm's picture.
Posted by: Realitystorm on 2025-12-31 07:15:36 Wiring. The white and black wires from the power supply connect to the red and black wires that connect to the board
Posted by: Byrd on 2025-12-31 14:45:09 Thanks everyone and happy 2026! @Realitystorm you've read my mind, that was next question on how/where the PSU was wired up internally @Phipli bit of a weird one, from cold the Mac Plus + Novy won't reliably start (the accelerator has orange and red LEDs - the red quickly fizzles out), after a few power cycles it boots reliably (orange LED stays lit then). Appears the Mac Plus only provides 0.5A, so time for some bench testing with crappy ATX PSU in hand 🙂 Be great to see it running reliably
Posted by: luRaichu on 2025-12-31 15:39:16 Measure the current draw with an ammeter. A multimeter should do this too. I'm lucky that my fancy Nemic-Lambda LA-200 variable power supply has a built-in ammeter. Comes in handy so many times
Posted by: Byrd on 2026-01-01 20:17:00 Multimeter lacks ammeter, but I've the requisite 5V 3A Meanwell PSU in hand - looking at @Realitystorm 's PSU - why do you think the neutral wire goes to the transformer? I'm assuming the brown wire is "active/hot".
Posted by: Byrd on 2026-01-03 16:08:57 Thanks, that did it - added a Meanwell 5V 3A mini PSU and wired up similarly to RealityStorm's unit (active/brown to 240V power switch and neutral to transformer). It's working well, the Novy upgrade really is fun and triples the speed of the Plus. I discovered the issues I was having were not necessarily power related but a jumper trace clearly open that I missed between two ICs. The fan is an original Pabst unit that came from another upgraded Mac with a bracket; it works well and extracts heat out of the top vents.
Posted by: Realitystorm on 2026-01-03 20:25:31 Glad my photos helped, FYI the fan for mine is mounted at the top of the case directly under the vent.
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