I'm doing a new build in a Sun Ultra 40 case.

In that case, there's a built-in 1000W power supply.

Is it safe / ok to use that if I know that my draw would be fine with a new 650W power supply (a i7 6700k and a decent graphics card)?

  • 5
    I would be surprised if they used the same motherboard connector. Nov 28, 2016 at 1:27
  • 9
    eh. A picture of the PSU label would be massively helpful in a definitive answer
    – Journeyman Geek
    Nov 28, 2016 at 2:31
  • 3
    Echoing the sentiment of Journeyman Geek, we need at least the model number of the PSU. As some other answers here have already indicated, the PCI-E power connectors may or may not conform to standards used by Nvidia and AMD. Indeed, I have seen fairly modern HP systems which used nonstandard 20 pin ATX board power layouts, presumably to prevent 3rd party refitting.
    – Adam Wykes
    Nov 28, 2016 at 3:07
  • 2
    @AdamWykes Without seeing HPs internal design notes I can't prove they didn't do it only or primarily to control the spares market, but if you're building in sufficiently large volumes like HP/Dell/etc do there're cost advantages from being able to ditch various legacy components in the ATX standard: -12V is only needed if you've got a com port, the 24pin connector devotes a lot more wires to 3.3/5v (and corresponding ground wires) than is needed for any modern system. (1/2) Nov 28, 2016 at 11:46
  • 3
    ... Modern PSU designs us DC-DC converters to make the 3.3/5V instead of tapping the transformer separately; moving them to the mobo and then having short HDD power cables come off from it gains a tiny bit in energy efficiency, but with 80+ only looking at the PSU itself and Energy Star having stagnated for many years I doubt they're doing it to collect green merit badges. OTOH if HP sells large blade arrays and/or prefilled racks with power generation/ups duties handled at the rack level where a pure 12V PSU setup has larger benefit it would let them share more resources. (2/2) Nov 28, 2016 at 11:46

7 Answers 7


The power supply will not power the system because it lacks connectors required by modern systems. Furthermore, the motherboard will not fit in the machine without modification.

The Sun Ultra 40 workstation (service manual) uses the SSI EEB form factor. The motherboard sits on a tray that has a cutout for the I/O panel, so you'll need to cut the I/O panel protrusion out of the tray after removing the motherboard. Furthermore, the SSI EEB mounting holes are a bit different from the ATX mounting holes; even if you are able to mount an ATX motherboard onto the tray, three of the holes near the processor are different. This limits the system's ability to safely withstand a heavy processor heatsink/fan (HSF) assembly, so you'll need to use a smaller, lighter cooler, which may limit your ability to overclock.

More critically, page 7-6 of the manual (PDF page 156, shown below) indicates that the power supply doesn't have the required connectors. The power supply has proprietary connectors that fit on the edge of the original Sun motherboard; while the 24-pin main power connector does look like an ATX12V connector (judging from the image posted in Dan Neely's answer), there is no EPS12V CPU power connector. The hard drive connector is also nonstandard, intended for a proprietary backplane; there is no standard SATA or Molex hard drive power connector. The PCIe auxiliary power connectors may fit, but don't count on it.

Page 7-6 of manual: Nonstandard power connectors

  • I'm tempted to think the power supplies are en.wikipedia.org/wiki/ATX#AMD_GES . No real proof tho
    – Journeyman Geek
    Nov 28, 2016 at 3:14
  • @JourneymanGeek the diagram on page 5-36 shows the 2nd PSU-mobo connector (P2) is about 2/3rds the size of the primary (P1). That appears to rule out AMD_GES, which had an 8pin secondary connector. Nov 28, 2016 at 6:40
  • Best left as "will not power the system without modification, will maybe work if modified." Nov 28, 2016 at 10:32

From my own experience with exactly that endeavour (wanting to re-use the attractive Ultra 40 M2 case for a regular PC) I can give you a heads-up, it will work. The supply can deliver about 750 Watts on the 12V rail alone, which is more than sufficient for the system you described. The "ATX-like" plug is actually ATX compatible, and Sun has stuck with the designated ATX colors. The thinner cable is used only for monitoring of fan speeds etc, and the PSU will start up just fine via the green pin power-on pin on the ATX plug However, for the harddrives and GFX extra power, you will need to build adapters yourself, or cut the extra power lead down and attach new plugs. If you have reasonable soldering skills, grab the power leads from an old normal PC power supply and fit it on the Sun ones, with good shrink tubes around the connections. Fitting a regular ATX mainboard is also quite some effort.. you will at least have to Dremel out the area on the back plate where the ATX cover plate will go, and add threaded holes for the mainboard stand-offs, since the original Sun backplate does not have anything near ATX-standard mounting holes. You're looking forward to quite a lot of electrical and mechanical handiwork, but you'll definitely end up with a cool looking PC when you're done.


Safe? Maybe. Compatible? Chances are no. The service manual indicates a design with two independant power supply connectors, and a very different layout from what I typically see in a PC. If the pinout is ATX compatible, it'll be fine. I somewhat doubt it though.

The power supply should be able to power at least two video cards fine

The PCI configuration includes two supplementary power cables used for either the NVIDIA Quadro FX4500/5500 or the Quadro FX3450/3500 graphics cards. The connectors appear in FIGURE 5-18 and FIGURE 5-19

This thread talks about replacing the PSU (along with many pitfalls such as non ATX compatible mounts and an odd shaped PSU)

Taking into account that it uses SAS drives (which indicate its semi modern) and the motherboard tray isn't standard, If you already have the case do due diligence. You're really going to want to check things like model numbers abd connectors

Some lower end models did take standard parts but chances are this isn't going to be a simple matter of throwing in a standard motherboard and everything just fitting in.

  • Looking at pages 5-22/23 and 5-34 in the manual, the GPUs are getting supplemental power from the motherboard, not directly from the PSU. That probably explains why the PSU has 2 big connectors to the mobo; but means that even if the first connector is ATX compliant you'd need to make your own breakout cable to use the the 2nd to power your GPU. Nov 28, 2016 at 6:38

I found a parts re-seller carrying the PSU for the Sun Ultra 40. While one of the connectors does appear to be a 24 pin ATX plug (the side that's visible matches wire colors and orders); the other connectors coming off it are all proprietary. It doesn't have the 8pin 12v CPU power connector, any molex/sata plugs for peripherals, and has at most 1 six pin GPU power header (there's a 6pin 12v header on a breakout cable, but I can't see if it has the proper keying for a GPU).

At best, you might be able to use a pin extraction kit to dismantle the proprietary connectors and use the wires from them to make the other connectors you would need. However without knowing what the I2C (an embedded control/data standard) connector is being used for, even that's not guaranteed. I'd lean against this being a show-stopper; but if it's used for monitoring/control purposes the PSU might refuse to start with it disconnected.

As a parting comment: Even if you could make it work, it's a 10 year old design meaning it'd be significantly less efficient than a modern PSU, and even your peak load (300-450W) is likely to be somewhat less than the 50% efficiency peak. In idle use it's going to be far worse than a properly sized modern design. And even that's ignoring that with about a decade of use on it, the original PSU that came with the work station is coming up on its own end of life.

Sun Ultra 40 PSU Images from Flagshiptech.com

  • +1 for mentioning possible use of a pin extraction kit - but he'll probably need a soldering iron, extra wire and pins, and heatshrink too, turning it from simple reuse of an existing PSU into an electronics project :) Nov 28, 2016 at 10:28
  • @rackandboneman the wire lengths look to short to make the 12v CPU connector directly, but you can use an extension cable as an alternative to splicing wires, and heat shrink's just cosmetic. Still unlikely to be worth it from a time vs money perspective; but probably not much worse than converting the case's mobo tray to hold a standard mobo. Nov 28, 2016 at 12:00
  • 2
    Uh protecting your solder splices in an environment where you can have 100 or so amps going through a short circuit is not cosmetic... Nov 28, 2016 at 12:23
  • @rackandboneman with what I was suggesting as the minimum, what splices? Pop existing 12v/ground pins from the P2 bogo connector, reinsert into an 8 pin 12v CPU plug, and then use an extension cable to extend it from where the short sun wires end to where the plug on the new mobo is. If you cut the old plug off and splice in longer wires to run it directly to the destination you would have splices to protect, and shrinking a wrapper around the entire bundle instead of just relying on tape around each individual wire would be a good idea, but my suggestion was to avoid having to splice at all. Nov 28, 2016 at 15:26
  • What are you suggesting to feed the drives and other stuff from? Nov 28, 2016 at 15:36

WooShell's post is correct. I am currently using a Sun Ultra 45 case and power supply with a MSI 9661 dual quad core Opteron board. The power supply indeed has a normal 24 pin ATX plug plus a proprietary 18 pin plug which provides seven 12v power on the top pins + two 3.3v. All the lower pins are ground. I found this out by attaching a mini itx board that doesn't require a 12v power connector, booting it and measuring the voltages on the plug. I've managed to plug in a 12v 4 to 8pin cpu power connector (takes a bit of effort). I've decided to dispense with the Ultra 40 board and tray and list it on E-Bay and simply drill and tap the bottom plate to accept 10mm standoffs. I will make a new backplate from aluminium as its easier, and attach it to the rear case opening.


I'm afraid to tell you this cause it will likely drive up the the cost of these used Sun boxes but ...Yes this works. And quite well actually.

The ATX style plug is indeed an ATX power supply plug. I bought a short ATX plug extender cable because it wouldn't reach my board.

For the 4/8pin CPU power I bought an 18pin plug/recepticle like this. I extracted a couple of pins from the cpu power cable of the first purchase and plugged them in to the right places on the 18 receptacle and boom: motherboard up and running.

The built in hard drive cages have 4 drive backplanes. If yours only has one search ebay for another. They're cheap and easy to install and half the reason to use this case. The power connectors on these connect right to the power supply. Couldn't be easier. The sata connector is a little more interesting but not difficult at all. Turns out the backplanes have an SFF 8484 connector which is a standard. So again I went to amazon and bought this which has 4 standard sata connectors to hookup to any board.

Mounting is the hardest part but actually not bad. As someone pointed out the sun board was an SSI EEB form factor not an ATX. However, the sun SSI EEB board and the ATX form factor share one screw in common. So I took out the sun cpu board and removed it from the metal tray. I took a dremel and removed all of board support standoff EXCEPT the ATX compatible one by the PCIe card openings with a dremel. Not too bad. I removed CPU back plates with my dremel. I then mounted my mother board on the one remaining standoff and marked the metal motherboard tray through the mounting holes of my board. Then it was a simple matter to drill and tap the tray for standard stand offs. I bought the combo drill/tap bit on amazon for a few dollars (link now points to a different product). And I bought this kit for the standoffs/spacers. I used tin snips and the Dremel to cut out an opening for the IO ports. Easy for someone familar with basic hand tools and now my motherboard lifts out easily on the tray.

I really like the internal fan tray but the fans draw too much power for an ATX motherboard so I bought plain 120mm pc fans and replaced the ones in the fan tray. They fit perfectly and I just pulled the cables through the fan holes.

You can use a few jumper wires to connect up the front panel power switch.

Now I don't know why I'm putting this at the end but there is one thing you REALLY NEED TO BE CAREFUL ABOUT. You need to select your motherboard carefully. The sun case blocks the first PCIe slot, otherwise if done correctly everything else works beautifully. I got lucky but what you want to do is buy a board with the M2 slot where the first PCIe slot goes otherwise your PCIe slot won't be usable. I am using this motherboard look carefully at the pictures and notice how the top PCIe slot is about an inch below the edge of the IO connector edge. Also make sure you have 8 sata ports so you can use all the drive bays.

I've been using this box with an AMD 5950x for 2 years and it's been AWESOME!

Next steps include building a small fan tray connector board to make it pullable just like the original. After that I'd like to build a better board for the front panel that has USB3 but all in all I've been very happy with this mod and if I could find another box for cheap I'd like to do it again and make a video.


Yes, it is safe. You will only draw as much power as needed. The 1000W is the max the power supply can provide.

  • 1
    Care to expand upon this? He's building a consumer machine in a workstation case with a similar but slightly different form factor that will impact how the parts fit.
    – bwDraco
    Nov 28, 2016 at 2:39
  • Some power supply designs will fail catastrophically if they are underloaded. Also, there are maximum (and sometimes minimum) wattages per voltage bus with computer power supplies. Nov 28, 2016 at 10:30
  • @rackandboneman, is there somewhere I could read more about underloaded catastrophic failure?
    – Adam Wykes
    Nov 28, 2016 at 13:35
  • -1 because there's no evidence provided that it will be safe - you can match voltages / current requirements and swap pins in connectors but there is likely to be some control signal/circuitry which may or may not be compatible and, unless documentation says otherwise, you're risking undefined behaviour which is not what you want from a PSU. You don't want to plug in your shiny new mobo, only for the PSU to become unstable & blow it up. For the price of a generic ATX PSU I wouldn't bother risking it unless one of the other answers gives you 100% certainty.
    – John U
    Nov 28, 2016 at 14:52
  • 1
    electronics.stackexchange.com/questions/80547/… ... there are a few scenarios described that could lead to trouble (12V PSU giving you 41V.....). And non-"standard PC" computers have a tendency to be made of parts that are extremely reliable if used correctly, but with little tolerance for intentional or careless misconfiguration... Nov 28, 2016 at 15:18

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