BillC

It's nice to hear you got it working, thought you should know that according to the 850 FSM that C109 is listed as a .001uF 25V capacitor. The only 1uF capacitor in the parts list is C35(16V/50V depending on version of FSM).

Atari released an updated ROM that fixed this timing issue and works with both NTSC/PAL systems, I believe this firmware is attached to the post linked below. The HyperXF firmware is also NTSC/PAL compatible.

I doubt it has code not present in the DD version since that one would be capable of both SD + DD operation. Mine does have a daughter-board which I presume is the data separator, I determined SD only operation by failure to perform a DD format with SpartaDOS. I acquired the AT88-S1 in a bundle on eBay about 10 years ago with my 1st 1200XL. I'm not that concerned with it only being SD capable, I also have 2-810s with the same limitation. I have other drives, Happy 1050/USD 1050/XF551, for DD floppy access.

I have one and prefer the 1050, which has more storage plus multiple upgrades available. The AT88-S1 I have is only single density, so the equivalent of an 810.

You failed to account for the low number pins being mirrored to the left side when viewed from below. When I do mods like this I prefer to solder to vias, cleared of solder first, instead of to pins. I notice that pin 15 has a connected via just to the left of pin 9.

You have to remember the way IC chips are numbered, and that this is viewed from below the chip. Pin 1 is at bottom left which puts pin 40 at bottom right, counting down from 40 finds the wires are connected to pins 32 and 26. EDIT: I misread the post, and realized afterwards the poster meant the CORRECT pins are 29 and 35.

The XL/XE computers have a single 8K ROM for internal BASIC, the ROM from a Rev C BASIC cartridge(brown cartridge/silver label) would work, but not the Rev A BASIC cartridge(brown cartridge/label) which contains 2-4K ROM chips. Some versions of the 600XL PCB do have thru holes for a 28 pin socket, even though a 24 pin socket is installed, and a couple jumpers can be moved to allow it to use a 2764 EPROM.

I just searched on Jameco: https://www.jameco.com/z/41464-10-Major-Brands-IC-41464-10-DRAM-256K-Bit-64Kx4-100ns-w-Page-Mode-HY53C464S-10-_41574.html

8bitclassics sells 5 video cables for the Atari 8-bits, 3 with additional connectors for monitors that support either S-video or separate Chroma/Luma. These are compatible with the Atari DIN5F monitor port, which is present on all but the 400/NTSC 600XL/XEGS. They also sell a composite to HDMI signal converter, I don't know how good it is but haven't had any issues with the video cables I purchased from them. Composite + dual mono audio S-video + Composite + dual mono audio Chroma + Luma + Composite + dual mono audio https://www.8bitclassics.com/product-category/computers/atari-8-bit-computer/

Rev A was also a cartridge for the 1200XL, Rev B didn't start until the 600XL/800XL.

No, in addition to the DIN connector the 600XL is also missing other components necessary for composite video output. The currently recommended composite/s-video upgrade for the Atari8 line is the UAV, available from MacRorie, the DIN jack and a few other components present on most other A8 boards would be needed for the 600XL as well.

You only listed the +12V current, the 4116 also uses +5V/-5V According to several datasheets the 4116 consumes 462mW active, 24 @ 462mW = ~11.1W.

With my Mosaic 64K card a "POKE 106,208" increases RAMTOP to 52K(208 pages of 256 bytes), allowing BASIC to see an additional 4K RAM, IIRC the default is 160(40K) It should be possible to use this cartridge in a left slot with an executable version of BASIC loaded from DOS.

You may have better luck on the ABBUC forums.

One issue with the Tandon mechanisms is supposed to be that the white pivot pins for the door tend to break.