• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

BGE's take on the Quadra 900/950 ATX PSU Mod


Well-known member
Since I have a Quadra 950, I actually have an interest in this project :)

I have no money right now (the stupid shelter in place has turned the US economy upside down and inside out, and our total income is $0 for at least the next two months xx( ).  When I last powered it on (at least 4 years ago now, I think), it worked fine, so I'm hoping it'd still work fine now, but of course, there's no guarantee of that.  Therefore, if I might, I'd like to reserve a set for down the road when I'll hopefully have some money to pay with, which should be sometime during July, August or September of this year, when I'm hoping things here will be mostly reopened).




Well-known member
Don't worry @CC_333, I understand. I have been in almost the same situation for the past year  :cry: . I thankfully found something recently that'll keep me busy and afloat.

I'll keep the extra sets on hand until someone wants them. Don't worry, one has your name on it. In the meantime, if you want to try your luck with the old PSU, I would recommend using a power strip that has a switch on it (plug everything in and then switch the outlet on). That arcing sound when you try to plug it in "casually" doesn't seem right. 

In other news, I've had some issues with the AC board. As you can see from the previous pictures, there used to be an earth plane pretty much everywhere but on the DC side of the relay. Apparently this can cause issues and it's best to remove it. Thanks to alumbrado on r/vintageapple for suggesting it. I have since done more research on the matter and it is indeed not recommended to have one.

Here is the new current design (v0.6):

Bildschirmfoto 2020-04-22 um 12.36.29.png

Bildschirmfoto 2020-04-22 um 12.35.43.pngBildschirmfoto 2020-04-22 um 12.36.01.png

The minimum distance (clearance and creepage combined) between AC and DC is now 10mm. Apparently (and according to a post on this thread), the minimum safe distance for 240V AC (in this case 240V is critical, not 120V) is 5.5mm so there shouldn't be any issues. I am now sure that I over dimensioned pretty much everything. The minimum clearance between the AC tracks (Neutral, Phase, Earth) is now 4.5mm. But we're talking tracks, not plated holes, so this is well above the 'acceptable distance' of 1.6mm. I've also had to take another look at the original board because depending on the type of load (inductive, resistive...), snubbers may be required. Delta didn't use anything to protect the relay from the monitor, so it should be fine without it. 

I am still having issues with the cables for this mod. I've found the original specs: https://www.wontex.com/products_3_b.php?gid=7

but I can't find new cheap ones that aren't bigger... I am now considering using 18 or 20AWG. More to follow.



Well-known member
I have good news. I was able to find cheap wires for both the logicboard harness and the AC input (AC board to ATX). 

18AWG for LB: https://www.arrow.com/en/products/1430-18-1-0500-004-1-ts/cnc-tech-llc

16AWG for AC: https://www.arrow.com/en/products/1430-16-1-0500-001-1-ts/cnc-tech-llc

Available in all colors, so the original aesthetic will be preserved. 

Black and red: 14ft each (that's 10x 40cm for each color)

Rest: 2ft each

-> price including terminals ($2.5 for 24): $16,52

Do you think it's too expensive?

Another option would be to skip buying new cables altogether and re-use the original cables. Unfortunately for me, I'll have to order new ones as I kinda damaged the original harness...

Technically the Becker also uses 18AWG for AC so you could theoretically use LB wires for AC. But for the price difference (80c), I'll sleep much better knowing that the AC wires are thicker. 

The 18AWG wires are a tiny bit smaller compared to the originals (16AWG), but they are more than enough (current wise) and they'll will fit better through the black cable tie thing. They're about 0.23mm smaller in diameter, which results in 5.5mm extra leg room! Awesome. The black cable tie thing is adjustable (it's just pretty much saturated with the OG wire config), so the harness will still be nice and snug. 

I'll update you guys with a BOM (list of parts) soon. 



Well-known member
I have created a new version of the AC board with the filter at the input (instead of at the output). Any comments or remarks would be well appreciated. 

I'm concerned about the track lengths... The Neutral track (Net- (FL1-Pad2) ) is 13cm (5 inches) long. May be too much... What do you think?

Bildschirmfoto 2020-04-24 um 18.28.55.png



Well-known member
Apparently the voltage drop and added resistance are really negligible. This version of the board will replace the older design. 



Well-known member
Well I've just bought a Quadra 950 that turns on for a second and then each second it drops power and fans spin down, next second up, then down.  Poor PSU must be suffering in there so I killed power quickly and started searching online.  And here we are!  Reading your journey from the first post to the last is a lot of fun - progress has been made for sure.  I am new to this project so am a little lost on where to start.  I like "step 1" but can figure most things out.  

Of course I've over in Australia so postage on anything is going to hurt.  The way this project looks now is :  You gut the Schwarzenegger size Delta power supply.  Install the AC and DC side to the exisiting chassis.  Take the internal components of a high quality ATX power supply and mount it in the Delta chassis also.  Connect everything and profit?  Hehe.  

I'll have to wait for photos of it installed to follow things but wow what a great contribution to the community sir BadGoldEagle



Well-known member
Hey there. You guessed the steps right  :smiley: . I'll come up with a more detailed guide later but that's pretty much it. 

At the moment I'm investigating the DC board clearances and I still have a few other small questions/issues before I can give JLCPCB the go ahead.

I've never sent anything to Australia but I think it'll still be cheaper than having boards made yourself (of course you'll still be able to do that if you want... I'll upload everything to GitHub once's everything done and tested). PCB Way was WAY overpriced and it still costs 30 bucks to have the boards sent out of China with JLCPCB (since the minimum order quantity for ONE board is 5, that makes 10 boards minimum and copper is heavy!)... 

A set will weigh 120g. It'll have some light padding but hopefully that'll help you estimate the shipping costs. Tell me if you're still interested in getting a set. 

Back to the Quadra.

Your 950 PSU exhibits the exact same symptoms as mine did after the recap. In my case, the 5V rail was causing this. I tried powering it on on its own with no load and there was 0v where there should have been 5. So don't worry, the logic board isn't to blame here. I had a professional PSU specialist look at the Delta unit and he couldn't find what was wrong with it... The diagnostic and the recap cost me a lot of money so I decided to cut my losses and start working on this mod. 



Well-known member
And the checks are done! Phew!

I am still not particularly proud of my fan circuitry. I am currently thinking about upgrading my dumb controller to at least PWM. But I am also tempted to go with a full-blown temperature controlled circuit that reuses the PSU's built-in controller... but for someone with limited electrical engineering background like me, that's rather complex. Here are my (rather basic) system requirements:

  • The minimum speed setting shall be controllable with a potentiometer or when possible trimmer.
  • The fan speed while unit is in operation shall be regulated automatically based on the PSU's internal temperature.
  • The actual fan speed shall be defined as the maximum between the temperature controlled speed and the minimum fan speed, whether the unit is on or not.
  • The fan shall be able to run at a fixed speed if the PSU's built-in controller is not plugged in. 

Truth Table:


Cold PSU


Quadra ON

Always on and at minimum

ATX controller OR minimum

Quadra OFF


ATX controller*

* May be used to cool down the PSU after the Quadra is switched off.



Well-known member
Proposed Comparator/Controller circuit:

Bildschirmfoto 2020-05-25 um 19.21.20.png

I had to take into account the different 2/3-pin fan control strategies (namely, PWM and Modulated ground) for the ATX PSU fan connector because since this isn't standardized, it has to work with them all. That's C1, R5-8 (on the right) and Op Amp #3. The other three Op Amps are used to compare the Potentiometer fan voltage to the ATX PSU fan signal. For those with Op Amp background, there's two comparator and one follower setups. Two power transistors Q2 and Q3 will effectively switch the two fan signals either on or off based on the table in the post above. I added a slide switch to disable/enable the comparison circuit (it disables the LM324's Vcc input and the circuit will function like before ie Potentiometer control only). For those who don't want to bother with this whole thing, just short 5 and 6 on SW1. You don't even need to buy the switch, I'm currently thinking about adding pads like on the IIc to short those pins:


© Big Mess o'Wires

Edit: For once, it was easier done than said. Kicad has some built-in solder jumpers!

I'll double check everything again and I'll update the PCB. 

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What other machines would this adapter be compatible with?  ie, use the same pinout as the Q900 & 950?



Well-known member
Hallo Bunsen :)

Thanks a lot for pointing out what it's called. The documentation will look a lot more professional now.

Zur Info, diese Dinge heißt 'ne Durchführungstülle. En Français (I'm a french dude living in Germany after all...), ça s'appelle un oeillet ou bien un passe-fil...

And yes, this mod is only compatible with Quadra 900/950s as they are (AFAIK) the only Macs with a 24 pin Molex Mini Jr (ATX motherboard) connector.

In other news, I've had to scrap the previous fan designs (they weren't compatible with high wattage fans and wouldn't work with all PSUs...).

It's now fully PWM and has a thermistor for fan control. A LED lights up once the thermistor reaches a temperature of 80°C/176F.

It's still work in progress but it's lookin' good!

Bildschirmfoto 2020-06-01 um 11.25.14.png



Well-known member
Good looking schematics! (to at least a laymen like myself).

Your revitalizing work with the Quadra 900/950 PSU makes me want to pursue my quest for a Quadra 9XX even harder than before! Thank you! :)



Well-known member
I've had to revise the fan controller bit again...

Bildschirmfoto 2020-06-11 um 12.34.16.png

Big thanks to the guys over at eevblog.com for their help. Although this still hasn't been 100% approved/verified, it's looking pretty good now!

[SIZE=1.4rem]We've mostly redesigned the LED controller circuit[/SIZE]

        - Now we won't be frying op amps with voltages that are too high at the inputs (updated R8 and Vcc for U1).

        - I've switched to an LM393 (U1)as this is a proper comparator. The 358 wasn't.

        - Inverting Schmitt Trigger built-in (R5, R6, R11, R12). LED will light up at 84°C and will turn off at 79°C. Just like your engine waring light, it should never light up. If it turns red, please stop carefully and contact your nearest service center (i.e. me).


If you don't want temperature control just remove TH1 and replace it with a 10k resistor. 

If you don't want the Overheating indicator circuit, just leave R5, R6, R8, R9, R11, R12, U1, Q3 and D1 out... this is not recommended but the fan will still work without it. Leave those components out at your own risk.

Edit/PS: I'll probably buy a bench supply and a breadboard to test this circuit before I send the boards to production...

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New member
So, 2 weeks ago I've acquired a Quadra 950 Workgroup Server 95 and happy as a clam with the thing. I managed to score 8x4meg parity SIMMs on German eBay, which I plugged in impatiently. Well, you can guess the final outcome. A poof, a small mushroom cloud and some searches later I end up in this post. Truly awesome work @BadGoldEagle! And I'm really curious to the current status of things as I'd very much be interested in a way to get her running again. 



Well-known member
@mietek sure thing... and that makes 10! Now, unless someone wants to buy 5 more, I'll stop the "pre-order" here. 

@Ton I feel your pain. It was pretty much the same thing for me but instead of RAM that was with the DOS card. And the damn PSU also tried to kill me (to be honest it was probably my fault).

I'm really starting to think there aren't any original working PSUs left...

And now, for the less fun part. A couple of weeks ago while casually browsing the web, I noticed that the MIC502 supplies aren't as high as I initially thought. I'll have to rethink the fan controller yet again (only for the 5th time). This on top of other life related issues, Apple ditching intel (which in itself almost caused me to fall into a depression), lead me to pause this project for a bit.

I need to sort out the life stuff first, but when I'll get back to it (hopefully in the next couple of weeks), I'll most probably pay someone to design the new circuit for me. I just can't handle another failure emotionally. This time, I'd like to use a 555 PWM generator type of circuit, but I can't figure out which one (there's at least 4 different variants) to choose. I'd like it to be still temperature controlled, and to have a minimum speed threshold (duty cycle) of about 40% so that the fan can't possibly stall. 

More to follow...



New member
So, I've opened the Quadra's case and power supply. The latter looked OK-ish, but on the motherboard something caught my attention. So, the first repair job is on the list.

Question; would I need to replace all of them, or will replacing the one that blew be enough?

Also; why did this one blow up? Wouldn't want to mindlessly replace this one only for it to be blown up again the next time.