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I have an Atari 1040ST with a half-bad power supply - Along with two 5v Red wires that Are good, there is a Blue wire that requires 12v .9A (aka 9mA??) - With A/c on, it's measuring at 10.73v (on the Blue wire, if you also have an Atari) causing my machine to cycle the Floppy drive when powered up to a beat of "we will rock you" steady clicking so, I'm pretty sure 10.73v is causing that - I have an external adapter that is 12v but 1.25A and another one that is 12v but .41A - I was reading one of the contributors here, Insta's answer which leads me to think I should use the 1.25A and definitely Not the .41A adapter - I will be splicing in to the Black Ground wire (there are 3 of these, I'll just pick one) and I will Cut the Blue and Splice the + going to that pin, bypassing the Atari PS altogether - I will then have the A/C AND the DC adapter on a Surge suppressor so that they power up at the same time - Should/Can I use the 1.25A adapter is my long question (sorry 'bout that!)

Tim Quack
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  • .9A = 900mA, .41A = 410mA. You might want to re-format your question, its a plain wall of text and hard to understand as it is. If I understood you correctly, 1.25A PSU will be more suitable than a 0.41A one for 0.9A load. – Wesley Lee Apr 19 '16 at 00:21
  • This question isn't exactly the same as that. OP is splicing in a supply rail to a multi-rail supply, not just replacing an external single adapter. – Passerby Apr 19 '16 at 01:09
  • Thanks Dave, but you are over my head on this one! – Tim Quack Apr 19 '16 at 05:53

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12V 0.9A means 12V 900mA, not 9mA, which is 0.009A. When replacing a supply, always go with the same voltage and equal or high current capability. So 0.41A is less than 0.9A, meaning it can't be used.

And yes, you essentially have the right idea. Cut the old +12V DC power supply wire out, splice the new +12V DC power supply wire in, and tie the DC grounds together.

Passerby
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  • Thanks for the 0.9 = 900mA answer b/c I was way off! Sounds like my 1.25 Ampere is my adapter way to go. And so, to be electrically safe: In my scenario, using the 12v 1.25Amp, would be correct? and my splicing is also accurate as well? – Tim Quack Apr 19 '16 at 05:52
  • I did my "Splice-in" idea with external 12v 1.25A PS and they measured correctly as working, but my Atari still is not doing anything (In fact now, it doesn't even make the clicking noise) Also, I "think" this is new: The light in the middle right (below 1040ST Logo) comes on with power, then dims way, way down quickly - My Red Wires were both measuring 4.95v before so, I can't believe since it needs 5v that 4.95v would cause problems - I press down all the Chips (carefully) before I did any of this to ensure seating's - I thought of buying a Atari PS, but it would seem like a waste of money? – Tim Quack Apr 26 '16 at 17:13