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Old 06 March 2010, 01:25   #1
Kakaboy
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Pc PSU mod for Amiga

Hey fellas,

I have an old pc PSU and would like use it for my Amiga 500 as the original is faulty .

I have tested the +5v on the PSU and it comes up strong with 5.3v but the +12v only reads 10.8v . How important is the 12v to Amiga ? Would this still be able to power up the Amiga or should I look for another PSU .

Cheers
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Old 06 March 2010, 01:35   #2
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Hi Kakaboy,

Is it an AT or an ATX PSU?

It it's an ATX, then some models have a minimum load on the +12V line required to get the full, stable voltage.
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Old 06 March 2010, 01:40   #3
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Quote:
Originally Posted by prowler View Post
Hi Kakaboy,

Is it an AT or an ATX PSU?

It it's an ATX, then some models have a minimum load on the +12V line required to get the full, stable voltage.

Hi mate , im not that technically minded , how can I tell ?

it has this on it :
Input rating : 115v-5A , 230v-2.5A , 50/60Hz
Output rating 200WMAX : +5v-20A , +12v-8A , -5v-0.5A , -12v-0.5A
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Old 06 March 2010, 01:50   #4
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Here's a pic

Last edited by Kakaboy; 02 May 2010 at 13:09.
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Old 06 March 2010, 01:54   #5
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Thanks for the pic!

That's an AT PSU, and should be suitable for use with an Amiga.

I can't figure out why the +12V line should be so low. Is your multimeter battery-operated? You could be getting a low reading at 12V DC if the battery is becoming discharged.
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Old 06 March 2010, 02:33   #6
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Quote:
Originally Posted by prowler View Post
Thanks for the pic!

That's an AT PSU, and should be suitable for use with an Amiga.

I can't figure out why the +12V line should be so low. Is your multimeter battery-operated? You could be getting a low reading at 12V DC if the battery is becoming discharged.
Multimeter is brand new . I have checked the 12v in my pc and its fine just not reading full 12v on the other PSU .

Will this work you think pr should I find anotherone .
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Old 06 March 2010, 02:42   #7
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It's just possible that it also has a minimum load requirement. I really can't believe it won't have sufficient power for your A500.

Are you testing it without a load connected? Perhaps you have an old hard disk that you could connect to one of the Molex connectors just to see if that results in a better +12V output.
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Old 06 March 2010, 02:43   #8
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Quote:
Originally Posted by prowler View Post
It's just possible that it also has a minimum load requirement. I really can't believe it won't have sufficient power for your A500.

Are you testing it without a load connected? Perhaps you have an old hard disk that you could connect to one of the Molex connectors just to see if that results in a better +12V output.
Yeah mate I was thinking that maybe it doesnt present a full current until its drawing power .

Ill give it a go .
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Old 06 March 2010, 02:56   #9
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Ok I have just connected HDD and the the power read 11.22v now .

Im getting closer lol
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Old 06 March 2010, 03:03   #10
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Well um, you need to match the specs and all the voltages on the underside of the Amiga brick PSU. Or did I misunderstand something?

AFAIK, most non-ATX PC-PSUs fail on one of the voltages... -5V or -12V? Or am I wrong.
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Old 06 March 2010, 03:06   #11
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What voltage do you get on the orange wire on one of the large white (motherboard) connectors?

That orange wire should give a reading of +5V DC if all voltages have stabilized.

If that hard disk is not sufficient load, the voltage on the orange wire will not indicate +5V.

The signal on the orange wire is known as 'PowerGood'.
http://pinouts.ru/Power/MotherboardPower_pinout.shtml
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Old 06 March 2010, 03:13   #12
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Quote:
Originally Posted by prowler View Post
What voltage do you get on the orange wire on one of the large white (motherboard) connectors?

That orange wire should give a reading of +5V DC if all voltages have stabilized.

If that hard disk is not sufficient load, the voltage on the orange wire will not indicate +5V.

The signal on the orange wire is known as 'PowerGood'.
http://pinouts.ru/Power/MotherboardPower_pinout.shtml
Yep im getting 5.3v
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Old 06 March 2010, 03:28   #13
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I would advise you to give it a go and see what happens.

Remove the lead with the 5-pin plug from the Amiga PSU and graft it onto the AT PSU.

http://www.hardwarebook.info/Amiga_5...0_Power_Supply

Take +5V from one of the red wires,
Ground from one of the black wires,
+12V from one of the yellow wires,
-12V from one of the blue wires, and
-5V from one of the white wires.

Also, it is a good idea to connect the AT PSU orange wire with one of the +5V (red) wires.

Good luck!
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Old 06 March 2010, 03:32   #14
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Quote:
Originally Posted by prowler View Post
I would advise you to give it a go and see what happens.

Remove the lead with the 5-pin plug from the Amiga PSU and graft it onto the AT PSU.

http://www.hardwarebook.info/Amiga_5...0_Power_Supply

Take +5V from one of the red wires,
Ground from one of the black wires,
+12V from one of the yellow wires,
-12V from one of the blue wires, and
-5V from one of the white wires.

Also, it is a good idea to connect the AT PSU orange wire with one of the +5V (red) wires.

Good luck!
Ok thanks mate . Will get onto it sometime tonight and will let you know the outcome .

Thanks for your help .
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Old 06 March 2010, 06:33   #15
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Quote:
Originally Posted by Photon View Post
Well um, you need to match the specs and all the voltages on the underside of the Amiga brick PSU. Or did I misunderstand something?

AFAIK, most non-ATX PC-PSUs fail on one of the voltages... -5V or -12V? Or am I wrong.
PSU has all compatible voltages .
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Old 06 March 2010, 08:27   #16
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Quote:
Originally Posted by Photon View Post
Well um, you need to match the specs and all the voltages on the underside of the Amiga brick PSU. Or did I misunderstand something?

AFAIK, most non-ATX PC-PSUs fail on one of the voltages... -5V or -12V? Or am I wrong.
You are wrong.

AT power supplies commonly lacks 3.3V
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Old 06 March 2010, 12:24   #17
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Quote:
Originally Posted by Kakaboy View Post
PSU has all compatible voltages .
Start reading:

http://www.ianstedman.co.uk/Amiga/am..._supplies.html

Last edited by vk3heg; 21 March 2010 at 01:45. Reason: caus...
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Old 08 March 2010, 11:34   #18
Kakaboy
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Quote:
Originally Posted by prowler View Post
I would advise you to give it a go and see what happens.

Remove the lead with the 5-pin plug from the Amiga PSU and graft it onto the AT PSU.

http://www.hardwarebook.info/Amiga_5...0_Power_Supply

Take +5V from one of the red wires,
Ground from one of the black wires,
+12V from one of the yellow wires,
-12V from one of the blue wires, and
-5V from one of the white wires.

Also, it is a good idea to connect the AT PSU orange wire with one of the +5V (red) wires.

Good luck!
Hey Prowler , I noticed the Amiga PSU does not have -5v ?
Also do I connect the Amiga shielded ground wire to the casing of the AT PSU ?
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Old 08 March 2010, 11:40   #19
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probably not needed as long as you have one of the black ground wires connected in the plug

so thats

+12v
-12v
+5v
Ground , black wire

4 wires in total
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Old 08 March 2010, 21:22   #20
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Quote:
Originally Posted by Kakaboy View Post
Hey Prowler , I noticed the Amiga PSU does not have -5v ?
Also do I connect the Amiga shielded ground wire to the casing of the AT PSU ?
Go with what cosmicfrog says above.

If you are not certain about the shield ground wire, I would suggest that you connect it to the AT PSU chassis only if this wire was originally connected to Earth (ground) via the Commodore PSU.
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