ATX PSU to A1200

[MarkAshley]

According to the back of the Commodore PSU I am currently using, the pinout is as follows:

1. +5v (Yellow/Red)
2. Not Connected
3. +12v (Brown)
4. Signal Ground (Black)
5. -12v (White)

According to this page:
http://www.hardwarebook.net/connector/power/atxpower.html

the connection should go as follows:

Amiga - ATX
1 - 19
3 - 10
4 - 3
5 - 12

On the ATX connector I have measured the voltage across 10-3, 12-3 and 19-3, and confirmed them as +12v, -12v and +5v respectively.

However, when I measure across 3-4, 5-4 and 1-4 on the Amiga side, the voltages I measure are much, much lower (less than a volt).

I'm guessing that this is because there is no actual load on the PSU? Can I safely connect the Amiga power connector as described above, or will it blow up my A1200?

Thanks in advance
Mark

[lopos]

AFAIK, you need to put a load on it to get the right voltage reading.

[MarkAshley]

That's what I thought. Now the tough question - do I take a chance and try it  :-?  :-?  :-?

[iMacMiga]

Here's a tip. I have a dead hard disk (the spindle is seized) that I used as dead load. You don't necessarily have to load the ATX power connector outputs, you only have to load the power supply so plugging a hard disk power cable into a hard disk (which when all said and done is low risk as you know that bit is wired up fine!!) and using that as load is a good dodge.
HOWEVER I've only ever modded AT and Mac PSUs which were hard-power, but I think the same rules apply for ATX.

I admire your caution. When I did my first AT -> A600 PSU mod i just wired it up, checked it looked about right and plugged it in

[MarkAshley]

Sorry, I don't understand. You seem to be suggesting I use a hard disk to put a load on the ATX PSU in order to get a voltage reading? Well the ATX PSU was correctly reporting the voltage when I measured it.

Or were you suggesting I connect the hard drive to the Amiga PSU to put a load on in, then measure the voltage while it's powered up, thus allowing me to confirm that the pinout is correct?

[orange]

is your Amiga PSU lightweight? if so, its 'switching' type so it needs load.
You could try to measure voltages while its connected to Amiga, but it would be a lot easier just to check on several Internet sites and with someone willing to measure it, usually its quite safe to do as hardwarebook says (for eg.)

[Stedy]

Hello Mark,

Did you connect pin 14 to pin 15 (PS-ON to GND)?

Without this connection the ATX PSU does not switch on the +5V outputs.


A guide with all you need to know on adding a PSU to your Amiga.


Bye,

Ian

[orange]

he's got problem with reading AMIGA PSU output voltages, not the ATX ones (as I understood)

[MarkAshley]

That's right Orange, it is the Amiga PSU I am having trouble measuring. And Ian, yes I have shorted pins 14 and 15 on the ATX supply to force it to power up.

[MarkAshley]

orange wrote:
is your Amiga PSU lightweight? if so, its 'switching' type so it needs load.
You could try to measure voltages while its connected to Amiga, but it would be a lot easier just to check on several Internet sites and with someone willing to measure it, usually its quite safe to do as hardwarebook says (for eg.)

Yes it is a lightweight PSU. What a great idea measuring while it's connected, don't know why I didn't think of it!!! I had already chopped the cable so had the wires exposed. I just twisted them back together and measured across them while the Amiga was turned on. Sure enough, the schematics are correct, and the voltages are what I expected them to be. On the strength of this I went ahead and wired it up to the ATX supply.

The power light on my A1200 doesn't work, so let me tell you waiting for the kickstart screen was agonising - but sure enough it works

Thanks for your help Orange!!

Mark

[Brian]

This link might help answerr your questions.