ATX power supply with -5V and big +5V +3.3V rails?

[Uniballer]

Is there a new high-quality ATX power supply on the market that is suitable for early ATX server boards? The early ATX specification included the now-optional -5V rail, and was much more +5V and +3.3V centric than the V2.x specs, which are mostly about feeding lots of 12V to the DC-DC converters on a modern motherboard. It would be OK to have a current-spec power supply as long as -5V is present and the +5V and +3.3V rails are beefy enough.

I did find these Logisys PSUs at Newegg, but don't know the quality level. What do you think?

If there is nothing suitable available new, what should I be looking for in terms of a quality early spec ATX supply with good longevity?

 

[Chuck(G)]

I like the Seadonic power supplies--they seem to have kept the -5V output.

 

[Uniballer]

I like the Seadonic power supplies--they seem to have kept the -5V output.

I like Seasonic, too, and have several of their PSUs, including some of the ones listed on your link. But none of the ones I have include the -5V rail. What current, or former, Seasonic model has it?

 

[Chuck(G)]

Oops, you're correct. Still not a bit issue--the -5V on pre-ATX supplies was rated at 100 ma or less. Easy enough to use a -5V linear regulator (e.g. LM7905) to take it from the -12. Add the mod to the motherboard and forget about finding "boutique" supplies. You could also do the same with a DC-DC converter, of which there are many.

What exactly is it that requires -5 on your ATX board? By the time of the 5170, this output was pretty much unused. The original 16-64K 5150 used it as a substrate bias supply for DRAM chips, but wasn't needed by the time of the 64-256K version.

 

[Uniballer]

I'm not actually sure that -5V is needed. The board documentation is not detailed enough to be sure. It's possible that something else is wrong, maybe even not enough +5V current. Tyan Thunder LE-T S2518 (claimed to be working by the seller, and I have $12 invested in this ) stripped down to 1 CPU and 512MB RAM. I know the CPU is running because I see the keyboard lights flash and when I hook up a speaker I hear an initial "beep" and memory-testing "tick" noises followed by the "no boot device" tones. The onboard video is not working. I plugged in a PCI video card that is known to work on a baby AT Pentium system, and I get no video out of that either (it might be the only BIOS I've ever seen that won't use external video in preference to onboard). I reset the CMOS just in case but haven't gone any deeper yet. I might have to set up a boot image that talks to a serial console to get an operating system configured, but how do I configure the BIOS with no video?

 

[Chuck(G)]

I suspect that the -5 is a red herring issue and not needed. The last Tyan mobo that I owned was an old Tomcat III, so I don't know about your board.

 

[Uniballer]

I suspect that the -5 is a red herring issue and not needed. The last Tyan mobo that I owned was an old Tomcat III, so I don't know about your board.

You were correct, as usual.

The Logisys power supply referred to above no longer includes the -5V line, even though the product description still has it. I found a used Zippy Emacs supply for cheap on ebay that does. It didn't make any difference.

I also found that an ATI Rage XL PCI video card plugged in to the 3.3V PCI slot on the Tyan S2518 gave me video (I don't know why the other card didn't).