Atari 65XE - 128K Upgrade

{From a defunct Atari site}

*** End-user accepts all risk. ***

Before you proceed you need to establish which version of the 65xe you have - there are a few different flavours.

Early versions had no ECI port, some boards were marked "900XLF", and some (later flavours) were marked (like its E/European cousin 800xe) were marked "130XE".​

for simplicity, you only need to examine the board for the number of ram chips inserted.

65XE's have two ram arrangements:

Layout 1:

2x columns of 8 sockets - 1 column of 8 being populated.​

Layout 2:

1x single column of 4 ram 4 sockets - 2 sockets being populated​

Note: if you have an ECI port then you have (essentially) a 130XE board so it can be upgraded to 128k
AFAIK - a non-ECI 65xe is non-upgradeable to 128k

Upgrade process - Layout 1

desolder resistor @ U34 (3 to do)
solder in a 20-pin socket
insert CO25953 into left side of socket, leaving four right-side holes free
insert/solder 8x 4164 ram chips​

Upgrade Process - Layout 2

desolder resistors @ U34 (3 to do)
solder in a 20-pin socket
insert CO25953 into left side of socket, leaving four right-side holes free
insert/solder 2x 4x64 ram chips (on my board the ram is HY53C464LS-10)
it's important you use 4x64 ram and NOT 4164 or similar​

replacing with 2x 44256 will give you a 320k 65xe!