Mystery Atari 800XL mod

[Dropcheck]

Okay..... I pulled everything. First tried just removing the OS mod. I replaced all the chips used. Completely lifted out the chips from their sockets in mass. Replaced all of them. Still no boot. Then I pulled the Ramrod XL memory board and replaced the 6520 chip. Left the 256k chips in place since R32 was still soldered in. Success......! Booted. I now have a working 800XL w/o the mods.

 

Now I just need to figure out what is bad and what I can put back in. I have no idea what version the Ultra Speed Plus is. Is there any way to find out? I didn't see any markings on the block. Also does anyone know if the CO21697 is a drop in replacement for the CO21696?

[BillC]

Okay..... I pulled everything. First tried just removing the OS mod. I replaced all the chips used. Completely lifted out the chips from their sockets in mass. Replaced all of them. Still no boot. Then I pulled the Ramrod XL memory board and replaced the 6520 chip. Left the 256k chips in place since R32 was still soldered in. Success......! Booted. I now have a working 800XL w/o the mods.

 

Now I just need to figure out what is bad and what I can put back in. I have no idea what version the Ultra Speed Plus is. Is there any way to find out? I didn't see any markings on the block. Also does anyone know if the CO21697 is a drop in replacement for the CO21696?

The Ultra Speed Plus is a block of 3 OS ROMs with a select switch, it consists of a stock Atari OS, the Ultra Speed Plus OS, and the XL FIX Plus OS. More info about it is available at NLE Audio