Likely PSU rating for Novy 020/030 accelerator?

[Byrd]

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

 

[Realitystorm]

From my quik30 plus. 5v, 2a, 17w

 

[Phipli]

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.

 

[Realitystorm]

Wiring. The white and black wires from the power supply connect to the red and black wires that connect to the board

 

[Byrd]

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

 

[luRaichu]

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