CV Gus Posted August 17, 2009 Share Posted August 17, 2009 With that "new" multitester, I measured the output from the 7800 adapter. It was 14V! I checked with the old analog one, and it came out the same- 14V DC. Why is this? When I run it off of a 12V battery I use the 9V setting on the adapter. That works. Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted August 17, 2009 Share Posted August 17, 2009 Measure the voltage with the adapter plugged into the console. It should drop to 9v or so. Quote Link to comment Share on other sites More sharing options...
nathanallan Posted August 17, 2009 Share Posted August 17, 2009 It gets regulated once it gets inside the console down to what it needs. 14V ought to be okay, but I wouldn't go too far over that. Quote Link to comment Share on other sites More sharing options...
Shawn Posted August 17, 2009 Share Posted August 17, 2009 18VCD 1.8A is the highest I've used without cooking a 7800. Quote Link to comment Share on other sites More sharing options...
shadow460 Posted August 17, 2009 Share Posted August 17, 2009 18VCD 1.8A is the highest I've used without cooking a 7800. What happened when you went over 18 VDC? Did it fry the regulator, blow a fuse, or something else? Quote Link to comment Share on other sites More sharing options...
Shawn Posted August 19, 2009 Share Posted August 19, 2009 18VCD 1.8A is the highest I've used without cooking a 7800. What happened when you went over 18 VDC? Did it fry the regulator, blow a fuse, or something else? 21vcd poped regulator yes. Quote Link to comment Share on other sites More sharing options...
gdement Posted August 19, 2009 Share Posted August 19, 2009 The input cap has a 16v rating, so that's also at risk if you go that high. Quote Link to comment Share on other sites More sharing options...
GroovyBee Posted August 19, 2009 Share Posted August 19, 2009 The regulator probably died at that voltage because its heatsink couldn't dissipate the power being dumped into it. Quote Link to comment Share on other sites More sharing options...
CV Gus Posted August 24, 2009 Author Share Posted August 24, 2009 (edited) What I mean is, why 14V? Why go that high; that's more than 50% higher than the needed 9V. Especially since things usually take a "jump" or "spike" when first plugged in. Why not 10V, or maybe 10 1/2V? I've run a 7800 off of a 12V battery, using an adapter that brings down the voltage to 9V DC (well, o.k., more like 10V...), without any trouble ever. So 14V seems unnecessary. Edited August 24, 2009 by CV Gus Quote Link to comment Share on other sites More sharing options...
CV Gus Posted August 24, 2009 Author Share Posted August 24, 2009 Measure the voltage with the adapter plugged into the console. It should drop to 9v or so. I did. But it doesn't answer the question as to why it's that high in the first place. Quote Link to comment Share on other sites More sharing options...
gdement Posted August 25, 2009 Share Posted August 25, 2009 Measure the voltage with the adapter plugged into the console. It should drop to 9v or so. I did. But it doesn't answer the question as to why it's that high in the first place. It's an unregulated power supply. The voltage will steadily decrease as more load is added, it doesn't hold constant like a regulated supply would. It's calibrated so that with the load of a 7800 console, it ends up at about the correct voltage the 7805 chip requires (or at least it should). This is cheap and ugly compared to a regulated supply, but it works. The 12v->9v battery adapter you used is a regulated supply (it will hold 9v with varying load). 1 Quote Link to comment Share on other sites More sharing options...
CV Gus Posted August 25, 2009 Author Share Posted August 25, 2009 In other words, it was a cheaper way of doing it. If so, that would be typical. Quote Link to comment Share on other sites More sharing options...
gdement Posted August 25, 2009 Share Posted August 25, 2009 Yeah it's cheaper. But typical of any game console, not just Atari. Quote Link to comment Share on other sites More sharing options...
Bruce Tomlin Posted August 26, 2009 Share Posted August 26, 2009 Also typical of over 20 years ago. You can't judge hardware from 1984 by 2009 standards. The lightweight switched power supply wall-warts that I've learned to love so much have only been around for 10 years or so. Back in 1984, switched power supplies were something relatively new, and not small enough to put in wall-warts. How to feed power to a 7805 was something quite well understood then, so it's not like they were just being cheap. This was something completely normal. Try the wall-warts for everything else from that era and you'll find the same behavior. They were nothing but a heavy transformer, a bridge rectifier, maybe a big capacitor, and (sometimes) a fuse. Quote Link to comment Share on other sites More sharing options...
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