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PSU modding for higher +5v output for retro PC

 
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post #1 of 1 (permalink) Old 02-29-2020, 11:43 AM - Thread Starter
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PSU modding for higher +5v output for retro PC

Hey guys I have nearly finished my first (and hopefully only) retro rig but the PSU situation has been the only thing holding me back from completion.

As I found out during this adventure, pre-mid 2000's, PCs were mainly +5v and +3.3v rail heavy with not much load on the +12v rail. The core of my retro rig is a dual socket 370 Pentium III workstation board so at the tail end of that era.

This all being said, it won't boot up even with a new Corsair HX1200i which should have enough +5v and +3.3v amps to turn it on I would have thought (has 30A on both of those).

I ended up buying an old Enermax PSU which has 36A on +3.3v and 45A on +5v and that powers it just fine - drawback being that it's 20ish years old and I don't trust the capacitors. I tried replacing them with new ones that I thought were the correct type per the numbers on the sides but after doing that the PSU itself wouldn't turn on - standby power is there and if you try to turn it on it will kick on for about 1 second but then go back to standby.

So this brought me back to an earlier idea that I want to see if you guys think would work.

It occurred to me that perhaps the 1200i won't boot the machine up due to low load on the +12v line that is what we've been using in PCs since mid 2000's, even though it should theoretically have enough amps on the other 2 rails for the old MB and since I want more +5v amps anyway:
Might it work to sever the +5v rail internally and instead of using that one, connect a +12v to +5v buck converter to the +12v rail and feed the +5v rail spot on the part of the PSU where all the modular plugs connect? That way there will be some load on the +12v rail, and I think i can find a 50A +12v to +5v passively cooled buck converter that should fit into the PSU housing.

What do you guys think?

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