BillC

Most likely a full clone of the Happy 1050 board, and the header is for connecting the optional controller board.

The 810/1050 mechanisms rotate at 288RPM while the XF551 mechanisms are 300RPM, Atari increased the read/write speed by 4% to compensate.

@Allan I uploaded a PDF of the APX Deep Blue C Compiler Manual to a8preservation in June, it's available from the website. http://www.a8preservation.com/#/software/release/1253

The 1200XL uses a 9VAC power supply and 2 internal +5V regulators, with component power split up between the regulators. This makes troubleshooting a power supply issue a bit more complicated.

Maybe the resistors were intended to be installed vertically, Atari did that in some devices.

How would that work? Male and female connectors have mirrored pinouts.

If a good number of these are original disks it would be nice if you would make a list and contact the "Atari 8-bit Software Preservation Initiative". You can also check the website to see if any of the original software you have is preserved or needs more dumps. A lot of software has been preserved(which means at least 2 identical copies at least 1 of which is from a flux dump), but I was surprised when I joined a few months back how much software that I considered common hasn't been.

The black label indicates that this 800XL was manufactured by Chelco, I think they only had the one manufacturing location in Hong Kong.

The AC power supplies are safe as long as you don't connect one with too high an output voltage, they are just a transformer and a fuse. The devices which use AC power supplies have rectifier diodes and voltage regulators. The XEP80 requires a driver in order to be used, this is normally loaded from disk although SpartaDOS X has its own version.

Most just cut the DIN cord of to use with another power supply. I have one I opened up for testing and am at the point I could remove the original PCB and swap in a replacement, but it's a fair amount of work. There is also a circuit called the C64-saver that can be added inline which shuts the power off if the voltage goes too high. The DV512-CM power supply was also used for the C64, Atari just used a different pinout and without the 9VAC direct from the transformer. https://www.retrorgb.com/c64-saver-2-released.html

These are also the correct power supplies for the Atari 810/1050/XF551 floppy drives.

The output voltage is a bit higher(9.5VAC instead of 9VAC) which would cause the voltage regulators to dissipate a little more heat, this may/may not cause a problem. The C014319 power supply is a good choice for use with the 850 interface which doesn't require as much current as the 400/800/1200XL, this is the power supply that came with my 1980 8KB 400 and was sufficient until I upgraded the RAM. The XL/XE power supplies that are heavy and have the "POWER SUPPLY DV-512CM" marking are commonly called the INGOT, and are well known for failing over-voltage and damaging chips. The box attached to one of the INGOT power supplies is an RF output cable, which connects from the computers RF modulator output to a TV antenna input.

The following is from my Percom AT88-S1 mechanism, this is a SSSD drive. It has a PCB attached to the top with a 34-conductor edge connector, there is also another PCB attached to the rear that appears to control the drive motor

For that one, you'll probably need to open it up and take photos. There were a number of upgrades that made it possible to do this, and without seeing the guts or having a name to put to it, there's no good way to tell which one it was. For the US/Canada this would most likely be a Happy 1050 or CSS Super Archiver upgrade, loading the backup software for these is a way to confirm without opening it up.

To me this board appears to likely be a prototype, given the voltage regulator footprint placement, missing traces between the SIO ports, other miscellaneous patch wires.