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Author Topic: A1200 Power Pinouts / ATX PSU / Molex Mod.  (Read 5746 times)

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Offline ArptasticTopic starter

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A1200 Power Pinouts / ATX PSU / Molex Mod.
« on: December 20, 2009, 11:41:44 PM »
Hi Guys,

I'm sure this has been done many times before - this is my take.

After sitting in a box for quite a few years got the old machine out but couldn't find a PSU, so had a google round and found this: http://www.ianstedman.co.uk/Amiga/amiga_hacks/Amiga_Power_supplies/body_amiga_power_supplies.html - which is an awesome page with all the detail needed.

I decided to put together a simplified graphic, it's not end-to-end but covers the important points.

Low quality - http://files.dustify.net/amiga/A1200-ATX-PSU-Low.jpg
High quality - http://files.dustify.net/amiga/A1200-ATX-PSU-Full.jpg

The high level process goes something like:

  • Take system apart down to motherboard
  • Solder molex socket onto motherboard
  • Strip wires on ATX PSU, attach to molex plug
  • Attach ATX PSU-ON wire (green) to ground
  • Try it
  • Increase size of 'Power' opening on case
  • Put it back together
I realise that this is not most ideal or aesthetically pleasing way of doing this but it's easy to do and hope the information will be useful generally.
 

Offline ZeBeeDee

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Re: A1200 Power Pinouts / ATX PSU / Molex Mod.
« Reply #1 on: December 21, 2009, 12:08:52 AM »
Nice job :)

Anyone taking on this job should be made aware that Commodore didn't always use the same colour scheme for the pins in the PSU's so if you attempt to do this mod then check the wiring first. Ian makes a cautionary note to the same end on his page as well so take note!

http://www.ianstedman.co.uk/Amiga/amiga_hacks/Amiga_Power_supplies/body_amiga_power_supplies.html#Rewiring_your_Amiga_power_lead

For those less skilled with a soldering iron, you can buy a ready made 250w PSU with Amiga power connection here:

http://amigakit.leamancomputing.com/catalog/product_info.php?cPath=39&products_id=866
« Last Edit: December 21, 2009, 12:15:52 AM by ZeBeeDee »
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Offline delshay

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Re: A1200 Power Pinouts / ATX PSU / Molex Mod.
« Reply #2 on: December 21, 2009, 05:44:29 PM »
you must also remember not to plug the A1200 onto a *un-modifyed* PSU connector as you can short out the -12 when the standard amiga power plug is connected.

the project should work for most users.

better still if you are very good with a soldering iron,solder a wire ( as thick as possible ) from the 5v power point to the 5v rail on the floppy connector,do this on the underside of the motherboard. this will help to reduce  the voltage jrop at the trapdoor when a card is fitted.
« Last Edit: December 21, 2009, 11:20:58 PM by delshay »
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power is nothing without control
 

Offline TheGoose

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Re: A1200 Power Pinouts / ATX PSU / Molex Mod.
« Reply #3 on: December 21, 2009, 10:18:16 PM »
Nice work and great info / pic - thanks!
G1200, A3000D, A1200 PPC AOS4.0C

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Offline ArptasticTopic starter

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Re: A1200 Power Pinouts / ATX PSU / Molex Mod.
« Reply #4 on: December 22, 2009, 08:16:27 PM »
Thanks for the responses guys.

delshay:

a VERY good point RE: not using an unmodified PSU / molex plug.

Also, nice one on passing straight to the floppy, is it worth doing this on any other parts (HD, PCMCIA, 150-pin etc.) ?
 

Offline delshay

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Re: A1200 Power Pinouts / ATX PSU / Molex Mod.
« Reply #5 on: December 22, 2009, 10:17:55 PM »
Quote from: Arptastic;534836
Thanks for the responses guys.

Also, nice one on passing straight to the floppy, is it worth doing this on any other parts (HD, PCMCIA, 150-pin etc.) ?



doing the power point to floppy makes a difference but it all comes down to the load on the trapdoor connector. you can check this yourself but must have a card connected at the trapdoor. check the voltage at the input power in,then check it at the floppy connector,note the differences in voltage.

now most users claims they have 4.95v on the card,i say check again this time put the meter ground probe on the card and the positive probe on the card 5v connection now what is the real voltage on the card. the art to having a stable A1200 is to get the voltage near to 5v across the motherboard with no voltage jrop at the floppy connector. no matter what you do you will lose around .03 volts at the trapdoor if all extra powerfeed is done correctly.

here on my system it reads 5.01v on the PPC card this is **KEY** to why i have a 80Mhz bus speed with 256Mb ram with Bvision attatched. if the voltage jrops to 4.8v on the card it  starts to crash.

i also have improved the ground tracks on the trapdoor connector and now shows .02 voltage jrop across the trapdoor at full load.

so if my voltage input is 5.04,the floppy connector will also read 5.04. on the Blizzard card reads 5.02.

you be suprise how more stable your system becomes there is no need to add extra powerfeeds anywhere else if the floppy power wire is done correctly.

also note that the groung wire thickness is also important for desktop users,so if anyone is going to modify the power point i recommend removing the old amiga socket and replace it with a new type of socket attached to the motherboard so thicker wire can be used to reduce voltage jrop. ( experts only ).


****ALL MODIFCATION AT YOUR OWN RISK****
« Last Edit: December 22, 2009, 10:50:03 PM by delshay »
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Offline ArptasticTopic starter

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Re: A1200 Power Pinouts / ATX PSU / Molex Mod.
« Reply #6 on: December 22, 2009, 10:48:34 PM »
Hah, great response - you clearly have a good understanding of this!

Unfortunately my A1200 is totally stock except a 2.5" IDE disk, although I am looking at expanding to an 040/060.

Will the lines still be supplied without an expansion card? - If this is the case I can at least go round with the meter and check the key points.

Slightly off-topic question: Is there a specification for the trapdoor expansion / pin-outs available - I have had a google but can't seem to find anything - I am interested to know how the accelerators / memory expansions operate - would also be able to find those 0v and +5/12 lines :)