Another 800 OS Board Mod

[AtariGeezer]

I found a different mod in one of my ebay 800's, anyone seen this before?

 

 

And a 128k Ram mod?

 

Edited May 18, 2013 by AtariGeezer

[+Roydea6]

Are there any Mod's to the main board at all?. Like cut traces or jumper wires.

[AtariGeezer]

Are there any Mod's to the main board at all?. Like cut traces or jumper wires.

 

Yep, two wires added to the bottom, but no cut traces.

 

[1050]

I've got a couple of 800s with a similar mod except mine have a switch on the ram board to turn off the Axlon ramdisk, one can be remotely mounted, the other is glued to the board. All three mods are needed to work the Axlon on mine, OS board with extra chips, ram board with extra chips and motherboard jumpers, I'm thinking mine has more jumpers for some unknown reason. And that's all mine do, a home rolled Axlon. I haven't found a perfect match to any published projects.

[ClausB]

Not sure about the OS board mod but the RAM mod looks like the Byrd 256K:

http://atariage.com/forums/topic/95299-david-byrd-256k-a800-memory-upgrade/

[AtariGeezer]

I've got a couple of 800s with a similar mod except mine have a switch on the ram board to turn off the Axlon ramdisk, one can be remotely mounted, the other is glued to the board. All three mods are needed to work the Axlon on mine, OS board with extra chips, ram board with extra chips and motherboard jumpers, I'm thinking mine has more jumpers for some unknown reason. And that's all mine do, a home rolled Axlon. I haven't found a perfect match to any published projects.

 

Something similar to this mod?

[AtariGeezer]

Not sure about the OS board mod but the RAM mod looks like the Byrd 256K:

http://atariage.com/...memory-upgrade/

 

Thanks Claus, I'll have to see if I can safely remove the chips on the Rom board and make a schematic of it.

Maybe pop it in the freezer to weaken the glue holding those extra chips down...

[ClausB]

Something similar to this mod?

 

Yes, that diagram is his original mod. Mr. Byrd and I spoke by phone back then and I told him the 74LS86 was unnecessary so he deleted it in Rev. A, which your board appears to have. I also told him his refresh circuit wasn't quite right but he got offended. Looks like he changed it a bit in Rev. A but I don't know whether it's right either.

 

BTW, Byrd's mod is NOT Axlon compatible.

Edited May 20, 2013 by ClausB

[Caterpiggle]

Holy cow, it is HEAVY modification for both cards ! NEVER SEEN like this before ...

[1050]

Something similar to this mod?

Yes, but only in the way that one is similar to yours too but still not an exact match. All three places have to be worked on and it's a memory mod. The similarities end there. My two have about the same number of backplane jumpers but it also has a switch to turn it off and on and it IS Axlon compatible, IIRC. Not sure where Byrd's fail that definition or if there is an easy way to make it compatible. It would have been nice to see both the early version and his later version instead of diagrams of one and text of the other. Really need both of both in other words. Maybe someday when the promised broadband gets here and I'm not on dial up any more, I could get interested in a search for both, but right now it's not gonna happen.

[ClausB]

Both Byrd and Axlon (and most every RAM extension) use the $4000-$7FFF banked region. The difference is in the location of the bank register. With Axlon it is at $0FFx and $CFFx. With Byrd it is at $D7xx.