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Naomi power consumption

invzim

invzim

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Hacked up a little setup to get some numbers to replace speculation about Naomi power consumption, how much the DIMM uses etc.

https://wiki.arcadeotaku.com/w/PCB_Power_Consumption

I was a little surprised to see that the most heavily used rail is 3.3V.

Naomi with cart uses 2.4A @ 3.3V, which is manageable - but with netDimm it jumped to 4.3A which is enough that width and length of cables come into play.

I didn't have the correct cables to add GD-ROM drive on top of all this, but GD-ROM is pretty obsolete anyway.
Also, both games were not encrypted - it could be that encrypted games use more power, but I have a feeling they don't.

Executive summary: the netDimm does indeed draw a fair bit of current.
 
Nice work @invzim, yes the most important "voltage" is 3V3 on this system which is a really bad design because it loses a lot through cabling.

Would have been better with a solid 5V to 3V3 step-down on the board or on the filter board but of course this adds to the BOM cost.
 
gdrom only has 5 and 12v run to it from the splitter cable, so that shouldn't affect 3.3 much if at all I'd guess.

Still that's an impressive increase. No wonder the capcom IO shits itself.
 
Wow that's even more than I'd have thought, thanks for taking the measurements!

I'd wager the Naomi 2 plus netdimm draws even more.
 
So it uses maximum 5A on it's 3V3 rail. Why is that considered "bad design"?
The wires leaving the power supply are pretty thick and they use 2 pins on 2 separate connectors of the filter board to connect the 3V3. Further on, the 3V3 is adjustable on the supply, so you can compensate for cable losses.
Modern pc ATX supplies can deliver up to 20 Amps on their 3V3 rail.
Some of them do have a thinner separate sense wire so that the voltage is measured at the connector and cable losses are compensated automatically.
If you change the originally cabling and install some longer cables with insufficient section, you are the "bad designer". If you use a power supply unable to deliver the needed 5 Amps, again, you shouldn't blame the original design.

If hikaru bga chips fall off the board, or chihiro gpu's overheat and fry themself when the fan stops rotating, that's "bad design"

You may dislike the way it was designed, but that's another thing.
Your naomi might have become more sensitive to voltage variations due to aging capacitors, but that's something difficult to avoid "by design" Let's also not forget that efficiency of step down converters has improved over the years. When the Naomi was designed, it made sense to have those hot electronics separate from your sensitive digital circuits.
 
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