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Old 11 June 2018, 22:38   #21
Stedy
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Originally Posted by XsamX1987 View Post
So basically would this of been more simple if I had just left the Power Supply Just the way it was before I removed nearly all the wires ?
Yep But considerably less educational.

You should read my detailed guide on all this:
http://www.ianstedman.co.uk/Amiga/am...su.html#ATXPSU

The top end power figure for an Amiga with PPC 7400/7410 + PCI motherboard and Zorro cards is around 150W. Clearly any reasonable, low wattage PSU will work. An A1200 with 68060, HDDs and SCSI card needs 16W, http://www.ianstedman.co.uk/Amiga/am...uredamigapower

I'll add the A4000+PPC 7400 power figures to the guide soon.

By the way, what was the power rating printed on the label of your PSU?

Ian
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Old 12 June 2018, 00:03   #22
XsamX1987
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Yep But considerably less educational.

You should read my detailed guide on all this:
http://www.ianstedman.co.uk/Amiga/am...su.html#ATXPSU

The top end power figure for an Amiga with PPC 7400/7410 + PCI motherboard and Zorro cards is around 150W. Clearly any reasonable, low wattage PSU will work. An A1200 with 68060, HDDs and SCSI card needs 16W, http://www.ianstedman.co.uk/Amiga/am...uredamigapower

I'll add the A4000+PPC 7400 power figures to the guide soon.

By the way, what was the power rating printed on the label of your PSU?

Ian
Thanks for the Reply and yes this is more Educational and fun

so your Guide will tell me how to How to fix my problem and what Resistor I need ?


I think this is what you asked for Its a 500w And Orange +3.3v 26A Red +5v 27A yellow +12v 22A Blue -12V 0.5A purple +5VSB 2.0A Black ground Green Ps-on Grey pw-ok

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Old 14 June 2018, 03:36   #23
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As said, it's nothing to do with a momentary switch - pulling (and holding) the _PS_ON signal low is the ATX standard method of activating the supply. The momentary action just feeds into the motherboard's power control circuitry that actually does the switching on and off of the PSU.

Also bear in mind that, for many ATX PSUs these days, it's the +12V rail that's the "primary" output and the one which needs to have a minimum load. This is due to modern PCs taking most of their power from 12V instead, in particular modern GPUs. As a general rule (but of course there are exceptions), the highest power output from a PSU like this is typically the main output and the one which needs to be loaded. So check which rail outputs the most watts, and then see about loading that. Sometimes a couple of old hard drives might be enough, but the best bet is a resistor.

A decent ATX power supply will shut itself down to protect the computer when it can't stabilise its output within spec. This could be because of the sense wire being disconnected as Stedy suggested, or simply not enough load. This is probably better than a lesser PSU that doesn't have the safety feature built in, which could happily supply too high a voltage to your Amiga.

Hey thanks for the Reply, Which wire is the sense wire and il go for the resistor, which one do I go for ?
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Old 14 June 2018, 11:24   #24
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Hey thanks for the Reply, Which wire is the sense wire and il go for the resistor, which one do I go for ?
That depends on the PSU you are using.
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Old 14 June 2018, 18:05   #25
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That depends on the PSU you are using.

Here is a picture of the Label

https://postimg.cc/image/syvh2gmd3/


Or 500w And Orange +3.3v 26A Red +5v 27A yellow +12v 22A Blue -12V 0.5A purple +5VSB 2.0A Black ground Green Ps-on Grey pw-ok

Last edited by XsamX1987; 14 June 2018 at 18:10.
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Old 15 June 2018, 09:02   #26
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Here is a picture of the Label

https://postimg.cc/image/syvh2gmd3/


Or 500w And Orange +3.3v 26A Red +5v 27A yellow +12v 22A Blue -12V 0.5A purple +5VSB 2.0A Black ground Green Ps-on Grey pw-ok
What I meant is that you need a schematic or reverse engineering of the PSU, because each one is different.
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Old 15 June 2018, 09:35   #27
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Sometimes - but not always - the datasheet or technical specs on the PSU manufacturer's website will list the minimum current required on each rail. That's what you need to be able to determine the correct resistor.

As for the sense wire, it will be a much thinner wire that goes to one of the terminals in the ATX connector along with a thicker wire, usually the same colour. So if it's on the 12V rail, look for two yellow wires going into one terminal, one much thinner than the other. That will be the sense wire, and there can be more than one.
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Old 15 June 2018, 17:02   #28
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Sometimes - but not always - the datasheet or technical specs on the PSU manufacturer's website will list the minimum current required on each rail. That's what you need to be able to determine the correct resistor.

As for the sense wire, it will be a much thinner wire that goes to one of the terminals in the ATX connector along with a thicker wire, usually the same colour. So if it's on the 12V rail, look for two yellow wires going into one terminal, one much thinner than the other. That will be the sense wire, and there can be more than one.
Thanks for getting back to me

I found the wire, a thinner brown wire with a orange +3.3v 26A on the 24pin connector

I don't know the Make as all it says on the sticker is Atx Switching Power Supply Model ATX-500B
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Old 15 June 2018, 18:59   #29
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Originally Posted by XsamX1987 View Post
Thanks for getting back to me

I found the wire, a thinner brown wire with a orange +3.3v 26A on the 24pin connector

I don't know the Make as all it says on the sticker is Atx Switching Power Supply Model ATX-500B



Last time I did one of these sense power PSU's, I had to connect the sense to the 3.3v rail. Then power supply would run fine.


Your PSU is just a Generic one. Nothing special. You tap in ATX-500B in google it comes straight up.
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Old 15 June 2018, 21:34   #30
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Last time I did one of these sense power PSU's, I had to connect the sense to the 3.3v rail. Then power supply would run fine.


Your PSU is just a Generic one. Nothing special. You tap in ATX-500B in google it comes straight up.
Ok so From looking at The Board and Reading online and from you said, I Connect a wire from 3.3v to 3.3vsr29 For the sense wire

Are you Saying I Probley Don't need a Resistor ?

I know its a cheap PSU But even putting ATX-500B Diagram in to google I still cant find it
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Old 15 June 2018, 21:51   #31
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Yeah, the sense wire needs to be connected to the 3.3V output by the looks of things. Whether you need a resistor after that depends on whether the PSU is stable as it is or not.
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Old 15 June 2018, 21:54   #32
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Sounds good to me, So Lets say I hook up my Multimeter for a few hours testing the Output to made sure there's no Major Loss or Rise would that be a good idea ?
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Old 15 June 2018, 23:15   #33
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Yeah, the sense wire needs to be connected to the 3.3V output by the looks of things. Whether you need a resistor after that depends on whether the PSU is stable as it is or not.
Sorry Forgot to Quote you in the Reply.
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Old 16 June 2018, 01:01   #34
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Hehe, no problem Yeah, just keep an eye on it. Ideally a scope would be better since then you'd see things like spikes and troughs, but in general, if a PSU is going to drift away from its target voltage, it will do it within the first minute. The 5V line is the critical one to measure, and anything more than 0.25V either way (on the motherboard) is probably too much.
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