I recently bought a plain Atari 800. I just cobbled together an SDrive-MAX and got it working powered by the USB connector, but when I connect the SIO +5V line and remove the USB power supply it doesn't work right. It sort of turns on, but the screen doesn't always show the whole display (sometimes there are thin horizontal "scanlines" over parts of the screen)* and disk functionality seems to be missing. It doesn't finish drawing its UI until after the Atari has gone into BASIC or Memo Pad. Going by posts like this one here (http://atariage.com/forums/topic/212003-what-good-is-an-850/?do=findComment&comment=2748745), which say that the 850 allows the SDrive-MAX to boot up completely before the A800 is turned on due to the 850's dedicated power supply, I decided to reconnect the SIO +5V line and run it through the 850.
*(I may be misremembering whether the "scanline" appearance still persists in the newest SDrive-MAX I've built, when it's being powered only from the 800 with no intervening 850; it's possible only my earlier attempt which was really broken had that problem.)
However, the result seems to be mostly the same; the SDrive isn't powered on at all until I turn on the 800, and when it does sort of power up, the Atari doesn't seem to be able to boot from it. When I go this route, the screen starts out with the "scanlines" but those eventually get replaced by the actual contents of the screen; but by the time I have the normal UI screen displayed, the 800 is already in BASIC. There doesn't seem to be enough time for the SDrive to finish initializing before the Atari tries to boot.
Will BigBen's mod (http://atariage.com/forums/topic/286669-sdrive-max-and-atari-850/?do=findComment&comment=4189162) allow me to power the SDrive from the 850 and 800 alone?
More SDrive-MAX questions:
Is it dangerous to wire the SIO +5V line to the Arduino and have it also plugged into a USB power supply? I would assume so.
Is there an editable (e.g. STEP or IGES) file for Kbr's XL-style case? I've printed it from STL twice, using somewhat different 3D printer settings, but both times the bottom plate is too long to fit into the top without trimming; that and the pegs that go up through the Arduino are just barely tall enough to be flush with the board; I'd rather have them stick up a little bit above it.
Also, backing up a bit, I'd like to know what's the story with the Option, Select, Start, and System Reset keys as pertains to booting programs and restarting the computer. I've been looking around on Google and in these forums (and in the 800 Owner's Guide) and haven't found much. Specifically, I'm wondering if the advice to hold one or more of those keys while turning the computer on, or hold one or more of them while hitting System Reset, pertains to all 8-bits or just to XLs and XEs (for instance, I know that holding Option allows you to bypass BASIC on XLs and XEs, since their BASIC is built in and not on a cartridge). I've tried various combinations of them while trying to boot the SDrive-MAX and haven't found any of them to do anything noticeable.