XEGS Eeprom problem and memory

[Crc_Error]

Quick question, I am repairing a XEGS system with a faulty corrupted oS.  I pulled the oS chip out and installed a socket.  I have a brand new eeprom chip and installed it with the proper XEGS bin file burned on it and the machine just has a black screen when I power up.   Putting back the faulty oS chip it boots up goes into test mode and I get the first bar red and the the rest is green in the Ram test and the Rom is all green with 40 squares.  Also is the XEGS suppose to display 40 or 64 squares for the memory test?  Could this be a timing issue with the characteristics of the eeprom?  Should I go with a 28256 instead or is it just fine with the 27256?  Thank you for any info.

[TGB1718]

I don't think it's a 27256 or equivalent you should be using, I think it's a 128k bit prom, so you would need a 27128 and even then there's a pin difference, pin 27 on the OS chip

is OE1 and on the 27128 its the programming pin, not sure, but are there links on the MB to allow using different chips.

 

Might be worth linking this thread here:- https://atariage.com/forums/forum/12-atari-8-bit-computers/

More hardware discussion there

 

OS ROM:-

 

27128 :- 

Edited September 19, 2021 by TGB1718

[Crc_Error]

Oops sorry on posting it in wrong section. Can thread be moved into hardware section easily....So sorry....But thanks for the info..

[ClausB]

27256 is the correct EPROM for the XEGS. It's 32K and it has OS, BASIC, and a game. 28256 is the EEPROM version.