ATX to Tanzania / 4400/7220 PSU adapter

[jessenator]

I've searched here (and elsewhere) without finding anything, but has anyone here developed a pin adapter to utilize an ATX power supply? The mount points and case size are close enough I'd call it identical, the pins? Probably not.

From what digging I've done, the Tanzania motherboard has two rows of AT-standard pin connector (using a not readily available molex connector).

The standards/schematics/pinouts are well documented for ATX, but I can't find the Tanzania PSU anywhere other than a p/n that leads me to outrageous prices.

A good friend of mine is an EE, but thought I'd ask to see if anyone ever made the attempt before we go diving in to find a solution from scratch.

If we make progress, I'll update it here for anyone else who needs a new PSU for their oddball Mac

 

[jessenator]

I've searched, but maybe I'm searching the correct terms. Is there a pinout diagram for the p/n 661-1248 PSU?

Well-documented ATX standard has this nice reference. It would speed things along to have a similar one for the Apple PSU.

 

[jessenator]

This is best lead I've got so far: https://www.macgurus.com/forums/showthread.php?15421-Tanzania-Power-Supply&s=a9a724cb3ead4281db2ef7cbfd04f8b4&p=19958#post19958

Unfortunately the WaybackMachine has no record of the image of the pinout he's referring to. Does anyone here know him? He mentioned forum member Trag (I think it's the same) in the thread above, but who knows if there's a connection there. Last activity on that forum was '13... the forum referenced was on "XLR8YourMac" forums, which don't exist anymore(?).

 

[Franklinstein]

Its an LPX standard power supply. It was an oddball standard in the mid-90s for cheap PCs. Why Apple adopted that instead of ATX we'll probably never know. Probably because that standard also usually used riser cards which allowed for some flexibility in system design for using a standard logic board in multiple case styles. 

 Anyway try searching for LPX pin out and see if you have any luck. 

 

[Franklinstein]

So I did some interneting and apparently the LPX standard preceded ATX, which is why Apple didn't use ATX at the time. Most LPX machines seem to have used AT-style power connectors with just the two connectors instead of four, and they typically also had hard power. I have seen a PC that uses the 4-connector LPX soft-power power supply, but I don't remember what it was; this was years ago and I pulled its power supply for use in my 4400 before scrapping the remainder.

UMAX also uses a weird hybrid LPX-style power supply in the S900 (and maybe others) but it's a single row connector instead of two separate connectors, in addition to a dedicated standby/power-on connector. On these, the wires all correspond to those on an ATX power supply so it's not hard to move one of these to a new ATX unit.

 

[jessenator]

Anyway try searching for LPX pin out and see if you have any luck. 

https://flylib.com/books/en/4.57.1.197/1/

Thank you!

Looks like this accounts for P1 & P2 connectors on the Tanzania power supply:



And wouldn't you know it, the colors actually line up!



Now to figure out what that second row is all about...

 

[jessenator]

Went off on a search train rabbit hole--
Here's something interesting: https://www.ebay.com/itm/202561989193
IBM? AIM alliance? CHRP specification? coincidence? Maybe not. IMB p/n 75H8483- too bad P10 has green wires :/  Can't find a pinout diagram anyhow.



I made what I posit to be correct: LPX (plus?) compared to ATX pinouts, side-by-side


Assuming black is always ground here. What could the orange be on bank 2? In my rabbit hole digging, there's a possibility it's proto-PCIe 6-pin molex? It does correspond with 3-ground:3-yellow (+12V??) pattern found on the molex 6-pin for PCIe. Again, conjecture.

The other "orange" label on the LPX is a "power_good +5V" connection. Looking at the PSU itself, one connector's worth goes to the daughtercard highlighted in magenta, and the other connector's wires go through a ferrite-shield connecting to the (top right in this photo) section of the main board.

The Tanzania PSU's do have soft-power. I wonder if that daughtercard controls that aspect of it...

 

[jessenator]

Ok, forget that IBM psu I mentioned above, check this out: https://cfusion.com/parts/index/REF_MAGNETEK_3523-15-200_CLONE.html

That looks exactly like the connections on the Tanzania PSU. MAGNETEK 3523-15-200 is the p/n. Used in IBM machines, so there's a CHRP connection again. No luck so far finding a schematic or pinout for it. I think this might be the winning ticket.

The only big difference is a master power switch on the back vs soft power on the 4400.

 

[jessenator]

More digging:
http://pinouts.ru/Power/MotherboardPower_pinout.shtml
gave me a lead to search other terms and this: http://www.playtool.com/pages/psuconnectors/connectors.html#aux



Now, the Tanzania PSU is 3 grounds and 3 orange. If I can interpolate a bit, (I looked at the motherboard and it says +3.3V :facepalm: ) that means 3x +3.3V pins on each with a total of 6x. With that assertion: ATX contains 4x +3.3V pins - what's the best course of action? This is where my ignorance will shine.

1) The ATX PSU has 2 fewer ground pins than the 4400 board requests; it also has 2 fewer +3.3V pins; Power good (not sure of voltage once stabilized); PS_ON# which I'm assuming is related to the power switch?

2) the LPX PSU has only 1 sense pin that normalizes to +5V when all voltages have stabilized; a -5V pin

That's mostly the start for the main power connections. As for the others:
- P3 is a floppy-power looking connector that I don't think was connected at all when I got it. ?for the PC/Cyrix card?
- a 3-pin white, red, black connection, which I think was for the front power button (which is a momentary switch anyway)
- the aux power on my donor is SATA, so I'll nab a SATA-to-Molex LP4 adapter (won't need the others...)

Edit: updated pinout of each connector:

 

[Franklinstein]

Looks good so far. The standby and power-on wires go through the little 3-pin connector on the original power supply though I don't know exactly which wire does what.

If you're going to replace the power supply for a new one I'd definitely recommend one with a hard power switch, though preferably one without the huge fan on the bottom (the 4400's case may restrict that a bit).

 

[jessenator]

So the ones I got for free are Dell branded out of xps8300 towers. No hard power, they've got some standby/ready LED on the back. They've got SATA aux plugs, but there are 4-pin molex adapters on the cheap out there.

After thinking some more my concern is regarding the destination requirements: there's a -5Vdc the ATX doesn't send. And then there's my ignorance. My EE friend said I could tap from the atx supply and get all the requisite +3.3Vdc outputs from there, as it's based on total current draw from the PSU. Guess I'll have to read up on how that works.

 

[jessenator]

So, I've stated it a couple times in various posts, but I have 0 electrical enginerering training. I know enough to know I don't know enough, but am willing to learn. Forgive the noobish questions and non-schematic drawings.

From what I gather, it's not as important to utilize the ATX's outputs as much as it is making sure the motherboard's requirements are met. If this is true: I need to create 2 additional +3.3V pins and a -5V pin. the PWR_OK is essentially the same as the power_Good from what I've read. tell me if I'm wrong there.

Here's the non-standard layout of pins just to match things up:


Here's what I'm thinking to solve the deficiencies:


I read a bit to know it's not good to tap off the +12V with three resistors to give me the volt output I need, but rather, use a buck converter. My question is can I get more than one output off of a single converter circuit? I'm trying to be efficient, but again, my lack of EE training tells me this kind of pragmatism won't get me anything but pops and smoke.

For the -5V, a voltage converter IC should work, correct? I'd use one of the extra +5V rails the ATX supplies, correct?

I guess also the grounds situation: can I connect the extra ground pins together? I know ground loops are a bad thing, but don't understand how they get created…

Thanks in advance for the guidance.

 

[NJRoadfan]

What the heck does the 4400 need -5V for? Early ATX power supplies had it (white wire, pin 18), but phased it out when the ISA bus vanished from PCs (very few ISA cards actually used it). You can likely safely omit the -5v line on a Mac. No need to "create" pins, you can y-split the 3.3v and 12v wires on your harness if you need extras. The +5VSB pin is always energized on ATX supplies, even when off as its the standby power pin.

 

[jessenator]

When I was reading about the lpx supply, I wondered about where that -5v would be routed. I really wish there was a schematic or something out there for the Tanzania board. I guess I could try to trace it. And the ATX has two +12V and the board only needs one. That was just me tapping off one of them, in theory, to supply the +3.3v auxiliary rails. But if it's safe to just use the 4 existing ones to split, I'll do that.

My uneducated guess is that they wanted to utilize a PSU that already existed as some sort of standard, with marginal surplus of supply. and IBM happily whipped out the old AT and they just went with it because cheap.

I wonder what those aux lines even go to...

At any rate I'm out of my depth and low on sleep. I'm going to try to find a replacement fuse for the one I broke and retry with the original. If that doesn't work, I'll harvest the connectors and just splice it into an ugly mess.

 

[NJRoadfan]

If the old power supply works and just needs a fuse, than replace it and test the voltage present on the connectors. The wire color is generally standardized between Mac and PC, so don't expect any surprises. The aux connector exists because the original AT connector lacked 3.3v rails (late Baby-AT 486/Pentium boards generally used a VRM to supply 3.3v to parts that needed it). Its likely the Mac doesn't need -5V at all, I don't see it present in the power supplies of other PCI Powermacs.

 

[jessenator]

Yeah, that's just it. I don't know if the old PSU works. The machine wouldn't power up when it was nasty looking. I stripped it down and from what I can visually see, no caps are bulging or blown diodes… I was pulling the fuse to see what the rating was, and it shattered pretty easily.

Problem is hardware stores around me don't carry anything near as small and beefy to meet the spec. And the electronic supply places are more industrial. Maybe I'll check just in case.

If I plug it in which pin should I test?

 

[NJRoadfan]

If the power supply has a real power switch, turn it on and see if the fan runs. Put the negative lead from your meter into a ground pin (almost always black) and use the positive lead to probe the various pins for voltage. Standard colors for various voltages on PCs is below

-Yellow +12V

-Blue -12V

-Red +5V

-White -5V

-Orange +3.3V

 

[jessenator]

Cheers!

It's soft-power from what I've seen—no switch. Maybe I can jumper the soft-switch just to see if it powers up.

 

[jessenator]

Got a free real-switch 400W ATX PSU and going to test it tonight. 

@NJRoadfan @Franklinstein , talk me out of just cannibalizing the connectors from the original PSU… no, really,  after compiling all this info, I'm a lot less timid about just splicing wires (vs traces on a board), and splitting those +3.3V lines. No electrical supply has what I need and I kinda just want to know if this 4400 will even work at this point without spending more money—granted $10–$20 isn't much, but I've way overspent thus far in my Mac'inings.

I'll double-check the measurements, but I'm certain that the generic ATX enclosure is the same size as the Tanzania PSU.

Bonus with this PSU I got is it still has regular ol molex connectors as well as a floppy connector for my CF-IDE adapter.