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Question about replacing the PSU in a Digidesign 13-slot PCI expansion chassis

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First post, by newnumbertwo

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One of my projects right now is to build out the most maximally-equipped OS9 PowerMac for audio production one can conceivably put together. To that end, I've started with a dual-1.25GHz MDD/FW400. Given that this project would require a LOT of PCI cards (mostly for offloading DSP processing), I procured a Digidesign 13-slot PCI expansion chassis.

Here's what I had running in the chassis (the PCI13BP model, specifically) until the PSU blew:

  • Digidesign Pro Tools Mix Core DSP card
  • Digidesign Pro Tools Mix Farm DSP card
  • Digidesign SampleCell II+ sampler card
  • Creamware Scope SP DSP card
  • Creamware Pulsar 2 DSP card
  • Keyspan SX Pro serial card

Additionally, I had a couple Adaptec SCSI cards as well as the Magma host adapter running in the G4 itself, not connected to anything (I use them for SCSI sample transfer with my hardware samplers), along with a USB 2.0 adapter card.

I had no issues with the chassis for the first 90 minutes. I was able to run PT DigiTest on the cards without issue (notable given how picky Pro Tools was about cards back then). I was able to run tests on the Keyspan SX Pro serial card with my serial MIDI interface. I hadn't gotten around to testing the Creamware cards yet before I heard a "pop" and the fans on the chassis and power supply died. The power switch on the front of the machine wasn't working to begin with, so I can't rule out a faulty switch as a factor yet, but I don't think it was the culprit. I think that this chassis was 15+ years old and probably left on a lot of the time, and the PSU died a "natural" death.

My question is about replacing the PSU. Here are the PSU specs:

3P PACIFIC POWER PRODUCTS
Model No.: KPP401-40 MAX. O/P: 400W
Rev: M-02

AC I/P
100-120Vac /8.0A
200-240Vac /5.0A
50/60Hz
AutoSelect

DC O/P
+ 5V 50.0A
+ 12V 27.0A
- 5V 1.0A
- 12V 3.0A
+ 3.3V 30.0A
+ 5Vsb 1.0A

The PSU uses a standard 24-pin ATX connector, but I have to say, those load specs seem fairly different than what I've seen in more modern PSUs. For example, just to compare the Corsair RM 750X, it supports a max load of 25A on the +5V & +3V, 0.8a on the -12V.

For those who have experience with PCI backplanes, how important is it to buy a PSU that conforms to the original spec? I have to say, I'm fairly ignorant about how power is distributed and what sorts of issues I might encounter. That said, I've found the same model replacement PSUs but they are not cheap, starting at $200 on the low end.

It's not likely that I've damaged the backplane, right? I would hate to get a couple hundred dollars into a PSU replacement just to discover the board was fried. I had the power provided by a Furman distributor and haven't had issues with any other equipment on the same circuit, so I think I can rule out power source as a culprit. I pulled the Creamware cards and popped them into the G4 just to make sure they were OK (and they were). I've got a fairly limited window to get a refund so am just wondering if anyone has any advice on next steps. I imagine a self-repair is probably beyond my skillset (unless it's something trivial like a fuse replacement).

Reply 1 of 5, by Horun

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Macs have diff power requirements depending on the model, my old PowerMac needs a PSU similar to one for an Athlon with very high 5v where most newer ATX PSU do not have that compared to PC ATX requirements.
Suggest you look for a Delta brand PSU as that is what was usually the brand used in Macs. Just a thought...
Added: and the pinout for some Macs PSU are not the same as PC ATX so you need to check to make sure which ever PSU you buy has same as a Mac not a PC.

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 5, by newnumbertwo

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Although it's connected to a Mac, it's not a PSU for the Mac itself but for the Digidesign PCI expansion chassis that I'm inquiring about.

Reply 3 of 5, by cyclone3d

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The backplane is most likely just fine.

I really doubt the cards you listed need anywhere the amperage of the old PSU.

The PCI spec requires that a max of 25W from all power sources cannot be exceeded per PCI slot.

So if ALL the power on your cards was only pulled through the 5v rail and they all maxed out the wattage rating, that would be a max of 150W total or 30A.

I can pretty much guarantee you that those cards don't do that.

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Reply 4 of 5, by newnumbertwo

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Just as a follow-up to this post, I wound up getting a replacement KPP401-40, described as "new"/open box. I paid $190, which is probably too much, but at least I have the peace of mind that I'm running the same PSU.

After installing the PSU, I noticed a couple changes - for one, the SampleCell II+ now shows an initial failure in ProTools DigiTest, but passes on the extended test. Also, the chassis power switch, which did not work with the old PSU, is working again. Not sure why that changed, but at any rate, it all seems solid now (except for the SampleCell test failure). I haven't tried using the SampleCell II+ yet but I'm gonna assume any issues with it are unrelated to the PSU failure.

Thanks, @cyclone3d, for the peace of mind.

Reply 5 of 5, by pentiumspeed

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for this reason, I would not do anything but buy Seasonic 700W, 750W, 800W or 850W, even 1KW Gold ATX power supply not the used one. Seasonic is highest quality and enough current on 5V, and ATX plug is 20 pin plus 4 pin that you can leave the other 4 pin unplugged with no concern.

The old power supply is noisy giving you issues with sensitive cards due to degraded capacitors inside the PSU.

Also if the cards does not have heatsinks, they will not exceed 10W each or *less*. If 25w, they *will* have active cooled heatsinks. By comparsion, 386 is less than 3W and is pretty hot. Even 486DX 33 is 4w and is hot to the touch but usually the chipsets on cards are less than that and temperature is less.

Cheers,

Great Northern aka Canada.

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