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BadGoldEagle

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

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Ladies and Gentlemen, 


Today, I would like to talk about the rapidly decreasing population of working Quadra 9x0 (900 and 950) specimens. If no action is taken within the next 5 or 10 years, the entire specie will soon disappear. Although the exact cause of death is still unknown, most researchers have concluded based on the symptoms that failing PSUs play a major role in the evolution of this disease. Experiments have proved that transplanting PSUs from younger compatible individuals saved almost all affected Quadra 9x0s. At this point in time, only one did not survive the transplant, with all other attemps being successful. The goal of today’s discussion is to specify a new effective PSU transplant procedure to save the remaining individuals from extinction. 

 

Joke aside, my objectives are the following:
1/ To provide an easy solution/kit to replace the dying original PSUs. I’m pretty sure ALL are bad at this point and the lack of schematics makes repairing them uneconomical and replacing caps before failure proved to be not enough in my case. I will be using @GeekDot’s brilliant write up as a base for my mod. 
2/ Make it so that there won’t be any drawbacks (which means creating a daughterboard to add back the square molex connectors as well as the monitor pass through feature)

3/ Make it silent.
4/ Meet or exceed the original PSU’s specs. 

 

But first, some additional background: The Delta PSU in the Q9x0 computers is a very strange animal. Because motherboard and CPU design changed so much in the last 29 years since the Quadra was first introduced, traditional modern PSUs don’t actually meet the old PSU’s specifications in some areas. While the original could happily deliver (back in its heyday) up to 33A on the 5V rail, modern high power PSUs struggle to output more than 25A. Some industrial-grade ATX PSUs on the other hand have to be compatible with old school systems, and that means that there are modern PSUs out there that are as powerful as the old Delta unit was. I plan on using a Bicker BEA-630 because it’s a modern, efficient, quiet (has a temperature controlled fan controller and operates most of the time without any fan at all) relatively small factor (ATX) PSU designed for 24/7 use (MTBF: about 20 years). I’ve found it for as low as 50 euros (which is really not bad for a brand new ATX PSU). 

 

There are unfortunately a few problems that need addressing: (ELECTRICAL ENGINEERING HELP NEEDED)

- The 'minimum output current‘ problem. Industrial grade ATX PSUs usually have a 'minimum output current‘. This is a common problem for ATX bench PSU modders. Basically (if I understood it correctly), the rail won’t be able to maintain the proper voltage unless there’s a minimum load. In the case of the Bicker, the minimum output current for both 5V and 12V rails is 0.5A. Some people suggest taking one wire of each rail and wiring it to ground through a 5 or 10 ohm, 10 watt resistor. If my math is correct, I’d need a 10 Ohm resistor for the 5V rail (5V = 10 Ohm x 0.5A), and a 24 Ohm resistor for the 12V rail (12V = 24Ohm x 0.5A). Is this correct? If so the additional power consumption would be about 8.5W, right?

 

- The 'there’s not enough pins' problem. ATX has 5x Ground and 5x 5V pins. The original PSU had 10 of each. Geekdot suggests to only populate every 2nd slot in the Q9x0 plug. In his excellent post, he proved that this arrangement worked and he was able to power up the Quadra. But with only half the pins, it probably halves the maximum current the board can take (‚probably‘ because we don’t know what the power repartition between the pins really is, so let’s assume it’s the same for each pin). Apparently ATX PSUs are designed so that each individual wire can deliver up to 6 Amps. So if I split one wire/post in two outputs, I can get about 3A max for each pin (assuming full load and without burning the PSU). Now the theoretical max. deliverable 5V amperage to the logicboard would be balanced across all pins and equal to 3A x 10 (# of 5V pins) = 30A which is almost the max. rated amperage (33A) of the original PSU for the whole computer. Of course, on the original Delta unit, not all 33A can go into the motherboard. So using one 5V pin from the Becker’s ATX 24 pin connector for two quadra 5V pins should be safe and will match or exceed the original specification. Any comments? I am no electrical engineer, so what is above might be completely wrong…

 

- There are other small problems but they’re easily solvable so I won’t bother you with the details right now. I’ll have to learn how to use Kicad properly and will probably end up taking lessons. But hey, that might turn out beneficial for me professionally so I think this is a cool and easy enough first project. 

 

If you made it this far, kudos to you!

Edited by BadGoldEagle

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Why would you need load resistors on the 12v and 5v rails?  The Mac will take care of that.  I added a resistor on the last SE/30 seasonic I did but that was on the 3.3v rail and I'm not sure that was necessary as it likely doesn't use that rail for regulation (but the spec sheet is unclear).

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Now that you mention it (and that I took a closer look at the spec sheet), I can indeed confirm that I won't need a resistor for the 5V rail. I didn't notice there wasn't a minimum output current required for 5V-Standby. I just blindly assumed that both regular 5V and Standby power came from the same 'source'... The soft power circuit will work great with the 5V-Standby supply and once the Mac starts, it'll certainly consume more than 2.5W! It also won't be using the 3.3V rail but since it's intertwined with the 5V one, it won't need any resistors either. 

 

But as far as the 12V rail is concerned, I still don't know for sure... I don't remember on top of my head what the SE/30 needs to start up (is 12V required?). One thing I know though is that on the Quadra, 12V is only used for Hard Drives and expansion cards. So what happens if I only have one card (the DOS Compatibility one) and no hard drives (only a scsi2sd)? I don't think it'll consume as much as 0.5A on its own... And if it doesn't, this might cause issues... What do you think?

 

PS: Also realized that the -12V rail is slightly weaker on the ATX (up to 0.8A) as it is on the Delta unit (1A)... but that should be fine!

Edited by BadGoldEagle
3.3V info

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Definitely following this one.  Especially if you can work out how to mount it without having to gut an existing PSU for its case—I have a working PSU but I'd like to swap it out prophylactically, as it were, but I don't want to destroy it in the process.

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Making an ATX case adapter would require too much metal work IMO. My plan is to reuse the original case without too many modifications (for example, I'd like to mount the new PSU without having to drill new standoffs, get posts/connectors for the original power plugs etc). But the original electronics won't be harmed at all (and could be reinstalled at will). For the first prototype, I plan on re-using the original cables and LB connector but I'll get new parts for the next builds.

 

BTW I bought long time ago a heavy duty industrial Noctua fan that's still silent. I plan on using it for the first prototype and for initial temperature checking etc. This is oddly enough the only fan in the case. If it didn't have to cool the entire system, I would have removed it. The new PSU will hardly generate as much heat as the old Delta unit, but the CPU will still heat up. 

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3 minutes ago, BadGoldEagle said:

The new PSU will hardly generate as much heat as the old Delta unit, but the CPU will still heat up. 

That is not so much of a problem. The CPU is a 33MHz 68040 processor and while it gets hot, it doesn't get *that* hot. A decent heatsink and a standard fan, mounted, say by the grill, should solve the problem of heat dissipation. i wouldn't be surprised if the 16 sticks of RAM generate more heat.

Also, bear in mind, with a substantially smaller PSU, there is also much more space free inside the Q950 case. You have seen yourself how big the Q950 PSU is.

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4 hours ago, BadGoldEagle said:

Now that you mention it (and that I took a closer look at the spec sheet), I can indeed confirm that I won't need a resistor for the 5V rail. I didn't notice there wasn't a minimum output current required for 5V-Standby. I just blindly assumed that both regular 5V and Standby power came from the same 'source'... The soft power circuit will work great with the 5V-Standby supply and once the Mac starts, it'll certainly consume more than 2.5W! It also won't be using the 3.3V rail but since it's intertwined with the 5V one, it won't need any resistors either. 

 

But as far as the 12V rail is concerned, I still don't know for sure... I don't remember on top of my head what the SE/30 needs to start up (is 12V required?). One thing I know though is that on the Quadra, 12V is only used for Hard Drives and expansion cards. So what happens if I only have one card (the DOS Compatibility one) and no hard drives (only a scsi2sd)? I don't think it'll consume as much as 0.5A on its own... And if it doesn't, this might cause issues... What do you think?

 

PS: Also realized that the -12V rail is slightly weaker on the ATX (up to 0.8A) as it is on the Delta unit (1A)... but that should be fine!

Don't forget the fans.  It will be easy to check. Just add all the specs up. 

 

The SE/30s video is 12v driven. 

Edited by superjer2000

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Well according to the spec sheet, the Noctua NF-F12 iPPC-2000 has a maximum power consumption of 0.1A... (mine's only a 3 pin BTW)

So I guess it'll be safer to put a resistor (or better, two in parallel) for the 12V rail...

 

 

33 minutes ago, ArmorAlley said:

i wouldn't be surprised if the 16 sticks of RAM generate more heat.

I've got 256Mb now. It's a good thing the fan will be close to the sticks! But now I think I should actually leave the ATX fan alone (it'll regulate itself based on the temperature inside the PSU) and add the Noctua as a fixed frequency fan to cool the rest of the computer (RAM + 68040 + 80486...). Because if the PSU fan turns itself off (that can apparently happen), the RAM and CPUs won't get cooled... Theoretically, it won't even have to start up as the Noctua will probably be enough to cool the PSU, it'll be there as some sort of failsafe.

 

Noctua 120 as intake and stock ATX fan as exhaust, how does that sound?

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Okay, I've done a quick mock up of how things are going to look. Because I haven't taken mine apart (yet), I've stolen one of Geekdot's pictures... (I hope that's all right with you, Geekdot!). 

 

There are basically two ways to go in order to mount the new PSU's PCB: 

1/ Make a metal adapter board (will add weight to the PSU...)

2/ Drill holes in the case.

 

Okay so I said above that I wouldn't be doing 2/ but that's going to be the most economical way. Plus the new holes will be hidden once the PSU is mounted inside the Quadra as they're going to be located on that ONE hidden side. That's what Geekdot did in his mod.

 

As you can see on the picture below, there are two additional boards involved here. One could be optional.

- AC Power adapter board (right): Will be used to connect the original plugs (monitor + main power input) to the new PSU, making the mod completely reversible. A board is kinda needed as I'll be using a relay to make the monitor plug work. The 3.3v rail will be connected to said relay and will only allow power pass through when the PSU is powered on (ie when the Quadra starts). This one will be optional as not everyone will want to save the monitor plug...

- DC Power distribution daughterboard (left): Will be used to convert the ATX plug to the Quadra's. It will also house a dumb fan controller (Sata connector for power, potentiometer to reduce RPM, fan header), the Soft Power transistor as well as the molex connectors. 

 

Both cards will be mounted using the original screws and a few plastic standoffs (like the ones used to prop up the small board with the two massive caps on the left hand side of the picture, no drilling required). Some industrial grade velcro will be added just for good measure.

 

Unless I can find a way to easily control the Noctua without any drawbacks using only the PSU's built-in circuitry, the fan layout won't probably change. Again, Noctua as intake, PSU fan as exhaust. 

 

Boards.thumb.png.c8f020c23d7c464607496d9dfbc4a51e.png

(original image from Geekdot's website, with proposed layout)

 

Again, if you have any suggestions, I'd love to hear them!

Edited by BadGoldEagle

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Hi guys.  I dont mean to hijack this thread but in doing some preliminary searches I came across this incredibly fascinating thread and wondered if you guys might tell me what happened when I powered on the 950 I just acquired.  Link to my post, 

I hope I did not damage the board.  Im not sure if I have the electrical expertise to do the mod as you suggest.  There is a PSU on eBay (for an arm and leg) that I may buy if it will get me running.  Thanks for any advice!

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This just proves my point. Those original PSUs are dropping like flies and can't be trusted anymore. I think I just barely understand how they fail now (I did some research on the AC side of the mod today, the schematic is almost finished). I've read a few stories online about people pulling the plug of their ATX PSU without flipping the switch first and this caused an arc in their PSU. Because remember, even though your computer isn't technically powered on, the PSU is still energized and generating 5 volts (that's your '5V standby' supply). 

 

Now, back to the subject at hand, the Delta SMP-291AB in the Q9x0es. It doesn't have a switch. It's basically on all the time. The thing is, I always have a live C13 (3 prong AC) cable on hand, ready to be used at any moment. It's plugged in behind the TV so I don't have to reach around the back whenever I need to plug in something. As is, it's not dangerous as the contacts are recessed (you can't touch them). But that's still where I made my mistake (@olliec420, I think that's what happened to you too). Because of the nature of the C13 connector, it's a tight fit: you can't fully insert it all the way in in one go, you have to wiggle it in... Because the cable was live, that also caused some sort of arc. I still remember distinctly hearing it before mine died. This is okay if this happens once or twice (definitely not fine!) on modern high quality PSUs, but for a 30 year old one, it's a killer!

 

I'm going to order one of these (I'll do a little more digging before I press the buy it now button, ideally I'd like one with a double pole switch...):

s-l1600.jpg

 

They're made for UPS systems (ie with an 'Uninterruptible Power Supply'). It's stupid, but I think it'll work. I plan on including one in the 'kit'.

 

Now, back to the hijacker for a minute (sorry buddy but things are what they are :)). In the end it's your choice. But if it was my money, I wouldn't buy it (plus you mention it being expensive...). Yes, it might work for a short while but we're talking minutes here, at most a couple of hours. Recapping it doesn't help apparently and trust me, you'll soon be annoyed by the loud fan and you won't really be able to enjoy it. I don't want you to think I'm saying this to sell my product, because frankly, I don't know if I'll really be selling this thing at this point or if I'll 'just' release the CAD files (and Digikey/Mouser parts list) as is for anyone to enjoy (I'll do it either way, but some people may prefer to get all components at the same time). As to the logic board damage, I can't say for sure, but since Geekdot had the exact same scenario happen to him (loud bang/small fire/arcs...) and since we was able to revive his lady Quadra with an ATX mod, I'd say yours is probably fine too. 

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10 hours ago, BadGoldEagle said:

I think I just barely understand how they fail now (I did some research on the AC side of the mod today, the schematic is almost finished)

 

This is all really good information for those of us who are slightly neurotic about killing our own PSU—thankyou!

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You're welcome. Just keep in mind that unlike the over voltage protection "extension cord" for the C64 PSUs, it won't do anything to protect it against sudden AC spikes. And I think that's what kills most of them. So I wouldn't use the Quadra when it snows, when it's windy etc... or do the mod and use it whenever you like ;)

 

Also, if you manage to find one with a two pole switch, keep me posted. This one will only disconnect the line/phase cable from the system. Two pole ones will disconnect both neutral and live wires. The relay I'm going to use for the monitor part of this project is of the DPST variety. In other words it'll allow me to completely switch off the monitor plug even when the system is off and plugged in.  

 

I also think it'll be much better if I don't make the monitor board optional. The initial goal was to make something that has the same internal AC connectors (the ones that connect the OG plugs to the boards inside the PSU) so that there won't be any modifications to the original stuff. 

 

Speaking of modifications, I've got one question for you guys. Feedback would be greatly appreciated.

Would you rather have a completely solder-less experience (at the cost of having the board look a little bit less professional), or would you rather have to solder three wires to your new PSU? 

 

I'm asking this because if we go with a brand new PSU, making any kind of modification to it will completely destroy the warranty, plus if you use another PSU than the one I'm planning on using and don't know much about electronics, you run the risk of soldering the AC wires to the wrong joints... The 'unprofessional' but simpler way to do things would be to cut a C13 cable and connect one end to the C13/14 original ATX PSU connector and solder each wire to the adapter board. That way there the mod will be just 'plug and play'. What do you think? 

 

PS/Edit: have ordered the Becker unit. Should get it in a few days.

Edited by BadGoldEagle

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I blindly thought that DPST switches only came in the 'thick' style. Apparently they can be slim too. I ordered the C13 switch and will let you know as soon as I get it if it's a DPST or just a SPST... Shouldn't make that much of a difference to be honest, but the former is theoretically safer. Most appliances (lamps etc.) probably only use SPST. 

 

I'll probably need external help for the schematics. I've read online that there should be a filtering circuitry in order to protect the relay. I have no idea how to wire it, plus it'll also need help for the actual PCB part (mostly with organizing planes etc). I'm telling you guys this because I have a lot of other work-related stuff coming up next week and I'll probably have no time to continue working on the schematics until the week after.  

Edited by BadGoldEagle

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Feel free to use what you want from the attached file - I've got no plans to do anything with it. I just hacked up the mAcTX adapter board and adapted it for a Quadra 900 series. In theory all you'd need to do to make it work is have a PCB made and use a 22 to 22 pin cable. In practice no idea - I only have a Quadra 650. A 24 to 24 cable might also work providing the Q950 has no components for the two extra pins to foul on.

 

For a relay board you're on your own. I left on a 2 pin connector - run a separate board for the relay. It's nice to try and keep mains off the primary board in case shit hits the fan. Include an anti tracking slot in between the AC pins. You want to minimize the path in case of an arc - and slots are great for stopping it. 

 

image.thumb.png.0b5b935aa192e285411e5961af2d3ddc.png

 

mAcTXc_3904_Q950.zip

Edited by Compgeke

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Thanks a lot!

 

The separation between the AC and DC side is indeed worrying me. I planned on using one of the sata connectors for the relay's coil. That has the advantage of completely isolating the AC from the DC board. But how exactly am I going to prevent shorts between AC and DC on the monitor board? I could design an air gap between the AC and DC sides of the relay, but is that going to be sufficient? Should I make 'substrate/core gaps' ? I don't know how to call them... but the type of isolation you see on the SE motherboards between the ports and the main circuitry.

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More or less just something like this:

 image.png.0af58862de77bb49a907021a10a673ce.png

 

Ignore that center track, it's an image I stole from the internet. Coil power would be on the left and coming in and the mains switching on the right. Keep traces and planes away from the mains side area that aren't needed - such as running anything DC over there. Red would be a couple slots to prevent arcing if something went wrong. Could do without them, it just makes me feel better with them there. Can never be too safe.

 

Edited by Compgeke

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Got it, thanks. So if I go with the sata connector for the monitor board switching system, it'd only run two DC traces over to the relay's position (3.3 or 5V and DC ground), no planes are required here. The relay itself should be long enough to place a few of those slots or a large one.

 

But would it be perhaps even safer if I were to include a small fuse for the 3.3V rail? What can I do to further protect the DC side?

Most importantly, what can be done in case AC goes into DC ground? The fuse for the 3.3 rail would probably fail open if AC goes in there, but what about ground? Sorry if those questions are silly, BTW...

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