How to combine AT and ATX power supplies to power same system (motherboard)?

Hello,
 
I am struggling to upgrade a certain medical system . The device I have contains an old motherboard which powered by an AT power supply.
My problem is that the power supply board (which supplies the AT power) has other functions, and there's no way to be replaced (by an ATX PSU). I already bought the motherboard: http://www.ibase.com.tw/2009/MB970.html , with INTEL core i5 CPU  Cry Cry. I can't risk my power supply board in attempting to operate the new parts (motherboard, CPU, 4 Gb RAM, CPU fan, SATA harddisk, and DVD), I believe it won't stand that kind of power consumption. I know you'll say this won't work at all -I know, but I was thinking about using voltage regulators to generate the 3.3 v rail from the same AT power lines.
OMG I really need help about:
How I can connect the AT and ATX power supplies to this motherboard (and to the other parts), ensuring that I am not risking my AT power board at all?. Another headache is that the AT power board has to work at the same time with the motherboard. And in order for the system to work the AT power board has to work (you know that a feedback circuit should be completed) that's why it should be connected to the motherboard.
 
This really became a challenge for me. I can't stop thinking, planning, and dreaming about it.
If you have any idea or any experience about this, I would like and hope to hear from you...

muhammad.shamut.7 (author) 2 years ago

Thanks guys for helping me :D. I just made sure of the cards connected on the motherboard. The only card I need to connect on the motherboard (which is ISA type) is connected with the AT-power board only by data cable (thank god) (pic #6) "I believe it is IDE, 44 conductor 2mm ribbon cable". The pictures of the power plug you see connected on the motherboard is for the old motherboard which I believe is customized (the motherboard) to work on AT-power (has inside regulators), so I can't use it with my new motherboard.

Are you guys suggesting me only to wire the grounds of both PSU's?- okay. I need to take the lowest possible power of the AT-power board.

Which PSU should I connect to the 20-pin ATX power connector??, also

which PSU is going to supply the harddisk, and DVD?.

Can I connect +12 V, and +5 V rails form the AT power supply to the ATX connector (as the power good signal is fed from them to the relays), while sharing its 4-COM's with the other ATX PSU on the same 20-pin connector. And filling all the other pins on the 20-pin connector from the ATX PSU??.

What I understood of your suggestions is that: For operating the motherboard with the AT-power board at the same time I only need to make a jumper to connect the PS_ON, along with one of the COM's on the ATX connector to the ON/OFF switch that starts the AT-power supply itself.

We need a circuit diagram, and our advice, though professional, is worth what you paid for it, and is to be confirmed by you on site, and in full possession of the facts. Right now I am inclined to agree with Mpilch, connecting the grounds together is probably all you need.

What items have a proprietary power connector (post pictures)? Don any of the cards connecting to eh motherboard have an additional proprietary power connector on them? If so does it look like that power input is completely isolated from the card slot? If so then you won't have a problem keeping the original power supply in place and adding the ATX PSU to run the motherboard. If it is connected then all you have to do is have both power supplies share a ground connection.

If it is a true AT Power supply then it has a separate power switch and doesn't have soft power and the need to connect to the motherboard to power on. Once again we need to see some pictures of the devices that have non PC standard power connections and the AT power supply in question.