Out of spec ATX power supplies when under load (JVS)

[defor]

So, I've been making a number of different adapter types for ATX to JVS, Modular PSU to JVS, etc...

And while the cables check out fine during testing, I've run into problems with majorly out of spec voltages on 3.3v on some power supplies.
Interestingly, it does NOT appear to have anything to do with actual current capacity, but instead something referred to as "Group Regulation"

It appears that group regulation has been responsible for similar system instabilities on modern PC's that do not follow the normal power usage profile between 12/5/3.3v

One such problematic power supply series is the Corsair CX (Green Label) series, and after encountering tons of problems with out of spec 3.3v on this exact series of power supplies I was led down the rabbit hole of people rating the CX green series as complete trash (disappointing as I have stacks of them from older retired PC builds, and Corsair USED to be rated as really good. It appears the newer CX (Silver Label) series should not have this issue, but I haven't tested it.

I mention all this because there's been recent interest in using ATX power supplies for powering JVS boards (i.e. Naomi), and some disagreement over the specs needed to actually power the PCB. In the end, it appears that the issues are directly related to this Group Regulation, and not actual under-spec power supplies. Especially as there's examples of Naomi running off 90W and 150W PicoPSUs also powering a netdimm AND JVS IO board.


So let's make a list- If you've got an ATX PSU and have adapted it to JVS and can test with a Naomi (or similar), measure the 3.3v lines AT the JVS power plug while attempting to power the Naomi up.


GOOD:
Antec BP350 (350W) - 3.2v
Diablotek PSEL400 (400W) - 3.2v

BAD:
Corsair CX450M Green Label (450W) - 2.6v
Corsair CX500M Green Label (500W) - 2.1v
Corsair CX600M Green Label (600W) - 2.2v
Athena AP-MFATX50P8 (500W) - 2.3v


Feel free to contribute!

 

[cruzlink2]

I completely agree with the assessment of the corsair cx the voltage under load dips too much. Had my Naomi 2 setup freezing all the time.

 

[defor]

I completely agree with the assessment of the corsair cx the voltage under load dips too much. Had my Naomi 2 setup freezing all the time.

I can't even get a good boot on any of them- the word seems to be that group regulation means that because the power profile doesn't match a normal pc power profile, other than putting arbitrary loads on each rail, actual current provided (even though the PSU is marked that it can definitely carry the 3.3v load) will be all over the place.

Can you post a list of PSU's that you have found working (and ideally a measurement of the 3.3v voltage AT the JVS plug while connected to the N1/N2?

 

[nismopunch]

It's funny I saw this thread because I just had a similar problem with a CX500 net booting a Naomi. Measured and sure enough it's fairly similar to the voltage you posted above. Right now using an old Antec TP2-550 with no voltage dip.

 

[djsheep]

Would be keen to hear of ATX PSU's members of the forum have got to work, especially if they're easily available.

It seems there are quite a number of group regulated "smart" PSU's on the market. I'm assuming "under voltage protection" could also essentially cause similar results?

Here's two PSU's that are group regulated / won't work with the Naomi. The 12v and 5v are generally ok, it's the 3.3 that seems screwy. The Naomi 1 read in at 2.6v and the Naomi 2 at 3.1v on both supplies

CORSAIR VS550
CASECOM PSCC-ATX700W

LITEON: PS-6301-08A

The above PSU was @xodaraP test bench PSU. Under load the PSU reads in perfect at the 5v and 12v, the 3.3v reads at 3.1v, but it boots the Naomi 1 with the Net DIMM fine every time.