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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: MarkAshley on October 07, 2005, 06:20:45 PM
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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
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AFAIK, you need to put a load on it to get the right voltage reading.
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That's what I thought. Now the tough question - do I take a chance and try it :-? :-? :-?
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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 :)
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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?
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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.)
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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. (http://www.ianstedman.co.uk/Amiga/amiga_hacks/Amiga_Power_supplies/amiga_power_supplies.html)
Bye,
Ian
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he's got problem with reading AMIGA PSU output voltages, not the ATX ones (as I understood)
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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.
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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 :D :D :D
Thanks for your help Orange!! :)
Mark
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This link (http://www.ianstedman.co.uk/Amiga/amiga_hacks/Amiga_Power_supplies/amiga_power_supplies.html) might help answerr your questions.